United States Environmental Protection Agency Motor Vehicle Emission Lab 2565 Plymouth Rd. Ann Arbor, Michigan 48105 EPA-460/3-81-002 March 1981 Air &EPA Dynamometer and Track Measurement of Passenger Car Fuel Economy ------- EPA-460/3-81-002 DYNAMOMETER AND TRACK MEASUREMENT OF PASSENGER CAR FUEL ECONOMY by Falcon Research & Development Co. One American Drive Buffalo, New York 14225 Contract No. 68-03-2835 EPA Project Officer: Jack Schoenbaum Prepared for: ENVIRONMENTAL PROTECTION AGENCY OFFICE OF AIR, NOISE AND RADIATION OFFICE OF MOBILE SOURCE AIR POLLUTION CONTROL EMISSION CONTROL TECHNOLOGY DIVISION CONTROL TECHNOLOGY ASSESSMENT AND CHARACTERIZATION BRANCH ANN ARBOR, MICHIGAN 48105 March, 1981 ------- This report is issued by the Environmental Protection Agency to disseminate technical data of interest to a limited number of readers. Copies are available free of charge to Federal employees, current contractors and grantees, and nonprofit organizations—in limited quantities—from the Library, Motor Vehicle Emission Laboratory, Ann Arbor, Michigan 48105, or, for a fee, from the National Technical Information Service, 5285 Port Royal Road, Springfield, Virginia 22161. This report was furnished to the Environmental Protection Agency by Falcon Research & Development Co., One American Drive, Buffalo, New York 14225, in fulfillment of Contract No. 68-03-2835. The contents of this report are reproduced herein as received from Hamilton Test Systems, Inc. The opinions, findings, and conclusions expressed are those of the author and not necessarily those of the Environmental Protection Agency. Mention of company or product names is not to be considered as an endorsement by the En- vironmental Protection Agency. ------- ------- TABLE OF CONTENTS Section Title Page 1.0 INTRODUCTION 1 2.0 SUMMARY AND CONCLUSIONS 2 3.0 BACKGROUND 5 4.0 TEST DESIGN 7 4.1 Dynamometer MPG vs. Track MPG 7 4.2 Tire Type/Tire Pressure Effects 8 4.3 Air Conditioning Effects 8 4.4 Effects of Highway Test Modifications 9 4.5 CVS vs. Meter MPG 10 5.0 TEST VEHICLES 11 6.0 TEST PROCEDURES 14 7.0 RESULTS OF FUEL ECONOMY TESTS 17 8.0 ANALYSIS OF RESULTS 18 8.1 Use of Ratio Measure for Fuel Economy Comparisons 18 8.2 Comparison of Carbon Balance and Volumetric Measurement 19 8.3 Estimates of Test-to-Test Variability 26 8.4 Dynamometer/Track Effects—Dynamometer Measured Fuel Economy Compared to Track Measured Fuel Economy 30 8.5 Tire Effects—Fuel Economy Measured with Radial Tires Compared to Fuel Economy Measured with Bias Ti res 39 8.6 Cold Tire Warm-Up Effects 42 8.7 Air Conditioning Effects 44 ------- TABLE OF CONTENTS (Continued) Section Title Page 8.8 Air Conditioning Simulation Effect 51 8.9 Effects of Modified Cycles 53 8.10 Computed Road Load Horsepower from Coast-Downs 56 9.0 DISCUSSION 60 REFERENCES 70 APPENDIX A COMPARISON OF MODIFIED AND STANDARD HIGHWAY CYCLES 71 APPENDIX B TEST VEHICLE-DESCRIPTION 77 APPENDIX C RESULTS OF FUEL ECONOMY MEASUREMENTS FOR DYNAMOMETER AND TRACK TESTS 87 APPENDIX D WEIGHTED LEAST SQUARES LINEAR REGRESSION OF VOLUMETRIC AND CARBON BALANCE DIFFERENCES 119 APPENDIX E TWO-WAY ANALYSIS OF VARIANCE WITH UNEQUAL VARIANCE ESTIMATES 121 APPENDIX F CALCULATION OF HORSEPOWER FROM COAST-DOWN TIMES 125 ------- LIST OF TABLES Table Title Page 1 Comparison: Dynamometer MPG vs. Track MPG, 1975 Models Source: TAEB Report 76-1 6 2 Test Vehicles 12 3 Relationship Between Effects Investigated and Test Vehicles 13 4 Baseline Test Results 15 5 Numbers of Individual/Averaged Dynamometer Runs 21 6 Estimates of Test-to-Test Squared Coefficient of Variation 27 7 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Radial, Air Off, Windows Up, Meter 1514 or Corrected) 31 8 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Bias, Air Off, Windows Up, Meter 1514 or Corrected) 32 9 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Radial, Air On, Windows Up, Meter 1514 or Corrected) 33 10 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Bias, Air On, Windows Up, Meter 1514 or Corrected) 34 11 Analysis of Variance Results for Vehicles with and without Air Conditioning for Selected Driving Sequences 36 12 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Radial, Air On + Air Off, Windows Up, Meter 1514 or Corrected) 37 13 Ratio ± 1 Standard Error of Dynamometer MPG to Track MPG (Bias, Air On + Air Off, Windows Up, Meter 1514 or Corrected) 38 14 Ratio ± 1 Standard Error of Fuel Economy Measured with Radial Tires to Fuel Economy Measured with Bias Tires for Dynamometer Tests 40 "IV ------- LIST OF TABLES (Continued) Table Title Page 15 Ratio ± 1 Standard Error of Fuel Economy Measured with Radial Tires to Fuel Economy Measured with Bias Tires for Track Tests 41 16 Ratios of BAGS Fuel Economy with Cold Tires to BAG3 Fuel Economy with Hot Stabilized Tires as Measured vs. Using Bias or Radial Tires in Track or Dynamometer Tests 43 17 Ratio ± 1 Standard Error of Fuel Economy Measurement with Air Conditioning Off to Fuel Economy Measured with Air Conditioning On for Track Measurements of Vehicles with Radial Tires 45 18 Ratio ± 1 Standard Error of Fuel Economy Measured with Air Conditioning Off to Fuel Economy Measured with Air Conditioning On for Track Measurements of Vehicles with Bias Tires 46 19 Ratio ± 1 Standard Error of Fuel Economy Measured with Air Conditioning Off to Fuel Economy Measured with Air Conditioning on for Dynamometer Measurements of Vehicles with Radial Tires 47 20 Ratio ± 1 Standard Error of Fuel Economy Measured with Air Conditioning Off to Fuel Economy Measured with Air Conditioning On for Dynamometer Measurements of Vehicles with Bias Tires 48 21 Comparison of Ratios of Air Conditioning/On to Air Conditioning/Off MPG for Track, Dynamometer and Tire Type for Selected Driving Cycles 49 22 Ratio ± 1 Standard Error of Fuel Economy Measured with Air Conditioning Off to Fuel Economy Measured with Air Conditioning On (Weighted Mean of Dynamometer, Track, Radial and Bias Tire Results) 50 23 Ratio ± 1 Standard Error of Fuel Economy Measured with Air Conditioning Off to Fuel Economy Measured with Simulated Air Conditioning for Dynamometer Measurements 52 ------- LIST OF TABLES (Continued) Table Title Page 24 Ratio of Modified Highway Test MPG to Standard Highway Test MPG for Dynamometer Tests (Air Conditioner Off) 54 25 Ratio of Modified Highway Test MPG to Standard Highway Test MPG for Track Tests (Air Conditioner Off) 55 26(a) Measured Coast-Down Times and Calculated Road Load Horsepower for Dynamometer and Track Tests 57 26(b) Measured Coast-Down Times and Calculated Road Load Horsepower for Dynamometer and Track Tests 58 27 Ratio of RLHP Determined from Track Coast-Down Tests to RLHP Determined from Dynamometer Coast-Down Tests (Air Conditioning Off/Windows Up) 59 28 Comparison of Dynamometer to Track Fuel Economy Ratios as Measured Over the FTP (Mean Ratio ±1 Standard Error) 61 29 Comparison of the Ratios of Fuel Economy Measured with Radial Tires to Fuel Economy Measured with Bias Tires for Dynamometer and Track (Mean Ratios ± 1 Standard Error) 62 30 Comparison of the Ratio of Ratios by Two Methods 63 31 Ratio (RQ) of the Mean Horsepower (P^) Due to Rolling Resistance Measured on a Small Twin-Roll Dynamometer to the Mean Horsepower Due to Rolling Resistance Measured on a Large Roll Dynamometer and Corrected to Road 64 32 Comparison of Dynamometer Power Absorber (PA) Settings in HP 66 ------- LIST OF FIGURES Figure Title Page 1 Relationship Between Dynamometer and Track Fuel Economies 20 2 Regression Lines for Differences Between Carbon Balance and Volumetric Fuel Consumption 23 3 Regression Lines for Difference Between Carbon Balance and Volumetric Fuel Economy 24 ------- 1.0 INTRODUCTION The Environmental Protection Agency (EPA) is required under Section 404 of the National Energy Conservation Policy Act of 1978 to examine and analyze the factors that contribute to the fuel economy differences achieved by actual road performance of automobiles as compared to the fuel economies estimated for these automobiles by EPA test procedures. EPA test procedures measure automobile fuel economy by operating the vehicle on a chassis dynamometer. This report is an analysis of data obtained under a testing program conducted by EPA's Emission Control Technology Division (ECTD). The analysis deals with a subset of the wide range of factors that contribute to fuel economy differences measured on a road in consumer service as compared to EPA estimates using a dynamometer. Specifically, this report analyzes the relationship between the fuel economy of production cars tested on dynamometer equipment and the fuel economy they achieve when operated over the same driving sequence on a test track. The test track simulates a subset of driving conditions that might be encountered in actual driving. The initial thrust of this report is to process the raw data and statistically analyze any differences. The physical significance of the results, supplemented wherever possible by other studies conducted by the ECTD, are then discussed and unresolved issues noted. ------- 2.0 SUMMARY AND CONCLUSIONS Analysis of the fuel economy data obtained in this program from dynamometer and track tests on eight 1976 model year production light- duty vehicles over the urban, highway, steady-state and modified highway driving cycles permitted quantification of the effects on fuel economy due to: (1) Dynamometer and track differences, radial and bias belted tire differences; (2) Fuel consumption measurement differences including carbon-balance-to-meter and meter-to-meter differences; (3) Air conditioning; (4) Air conditioning simulation procedure for dynamometer; and (5) Coast-down time differences between dynamometer and track. Results of the analysis showed: • Fuel economy in miles per gallon, as determined from fuel consumption measurements over the urban and highway cycles, ranged from 5% to 12% higher on the dynamometer compared to track for vehicles tested with radial tires. For vehicles tested with bias tires fuel economy over the urban and highway cycles ranged from 5% to 15% higher on the dynamometer compared to track. • On dynamometer tests over all cycles, vehicles equipped with radial tires obtained generally lower fuel economies than vehicles equipped with bias tires. On track tests vehicles equipped with radial tires generally obtained a higher fuel economy than vehicles equipped with bias tires. However, the fuel economies compared in this way depend greatly on the type of radial and the type of bias tire as well as the vehicle tested. • The relationships between fuel consumption measurements from flowmeter and carbon balance methods are reasonably well fitted by straight lines in fuel consumption space. ------- These lines have offsets that vary from meter to meter However, the slopes are consistent for all meters and imply that carbon balance fuel consumptions decrease relative to meter fuel consumptions at a 5% rate. In general, meter measured fuel consumptions were greater than carbon balance fuel consumptions by as much as J>%_ over the range of measured fuel consumptions. No conclusions could be drawn with regard to absolute accuracy of the fuel consumption and fuel economy measure- ment methods. Operation of a vehicle's air conditioner resulted in an 8% to 17% decrease in fuel economy as measured on the track over the urban cycle. Over the highway cycle the decrease in fuel economy due to air conditioning ranges from 5% to 12% as measured on the track. The simulation of air conditioning on the dynamometer by a 10% increase in the P.A.U. setting of the dynamometer above certifica- tion value produces no significant change in fuel economy as compared to certification P.A.U, setting. For the five variations of the EPA highway cycle investigated, fuel economy effects measured on the dynamometer were directionally consistent, and statistically equivalent in magnitude to the effects seen on the track. The results showed: (a) Cold starting decreases EPA highway mpg by 10% (b) The noisy highway schedule produces a 3% lower mpg compared to the EPA highway cycle (c) The redistributed highway schedule produces a 4% lower mpg compared to the EPA highway cycle (d) The smooth highway schedule produces a 5% increase in mpg compared to the EPA highway cycle (e) A 50 mph highway cruise produces an 8% increase in mpg compared to the EPA highway cycle Coast-down tests conducted en six of the eight vehicles in the test program permitted total road load horsepower calculations at 50 mph on each of the six vehicles for both track and dynamometer tests. The results showed that total ------- road load horsepower estimates were generally lower on the track than on the dynamometer. This result is not consistent with the fact that the fuel economy estimates are larger on the dynamometer as compared to track. However, road load horsepower calculations were con- sistently higher for bias tires than for radial tires on track tests and were consistently higher for radial tires than for bias tires on dynamometer tests. This result is consistent with the fact that the rolling resistance of radial tires is generally lower than for bias tires on track tests. Recent studies by EPA not within the scope of this program indicate that small twin-roll dynamometers do not properly simulate vehicle road loads because of velocity differences measured between the front and rear rolls of the dynamometer when operating over a driving cycle. In accordance with Federal Test Procedures, small twin-roll dynamometers operate with their rolls uncoupled from each other. The front roTl is coupled to flywheels and a power absorption unit, the latter simulating the aerodynamic force experienced by a vehicle. The rear roll drives a tachometer that measures vehicle speed. When the dynamometer rolls are coupled together, preliminary tests indicate that dynamometer to track fuel economy differences may be reduced by about 6%. The remaining dyno- to-track mpg differences are probably explainable by the tire/surface interaction differences. ------- 3.0 BACKGROUND The fuel economy data obtained from eight 1976 light-duty passenger vehicles and analyzed in this report represent data obtained in the second phase of a program designed to investigate dynamometer/track fuel economy differences. In the initial phase of the program, six 1975 productions cars were operated on EPA dynamometers and on the Ohio- Transportation Research Center test track.1 The EPA City and Highway cycle test results for these six cars are summarized in Table 1. The dynamometer tests included standard EPA City tests (3-bag 1975 FTP's) and Highway tests, from which combined 55/45 dynamometer fuel economy values were calculated. Since no systematic offset between carbon balance and flowmeter mpg measurements was observed in these tests, the results of these two measurements were averaged for each car. The city tests conducted on the track employed onjyjiot. .starts, so a weighted cold start/hot start value for the track Testing had to be estimated. This was done using each car's ratio of 1975 FTP fuel economy to hot LA-4 fuel economy, as observed in the dynamometer tests. The resulting "75 FTP" track mpg values were then used with the raw highway cycle track data to compute 55/45 track fuel economies. The "dyno/track" mpg ratios in the table are thus the result of comparing dyno and track 1975 FTP mpg, highway mpg, and 55/45 mpg. The averages of these ratios are given at the bottom of the table. ------- Table 1 COMPARISON: DYNAMOMETER SOURCE: MPG VS. TRACK MPG, 1975 MODELS TAEB REPORT 76-I1 A. DYNAMOMETER MPG '75 FTP -Carbon Bal . - Flowmeter Average Hot LA-4 - Carbon Bal . - Flowmeter Average Ratio, '75 FTP/ Hot LA-4 Highway - Carbon Bal . - Flowmeter Average Dyno 55/45 MPG B. TRACK MPG Hot LA-4 - Flowmeter "75 FTP" Track Highway - Flowmeter Track 55/45 MPG C. DYNO/TRACK RATIOS City Highway 55/45 VW RABBIT 90-M* 24.4 23.8 24.10 26.1 25.0 25.55 0.943 36.9 34.5 35.70 28.23 24.0 22.63 33.7 26.56 1.065 1.059 1.063 FORD PINTO 140-M* 17.8 17.6 17.70 18.9 18.6 18.75 0.944 28.1 27.6 27.85 21.17 16.6 15.67 25.5 18.96 1.130 1.092 1.117 PONTIAC FIREBIRD 250-M** 17.0 17.3 17.15 17.4 17.8 17.60 0.974 24.4 25.3 24.85 19.93 16.4 15.97 23.8 18.75 1.074 1.044 1.063 FORD GRANADA 250-A* 13.0 13.1 13.05 14.0 14.1 14.05 0.92.9 18.2 18.9 18.55 15.06 12.5 11.61 16.5 13.40 1.124 1.124 1.124 CHEVROLET CHEVELLE 350-A** 14.0 13.4 13.70 14.6 13.7 14.15 0.968 19.4 18.7 19.05 15.68 13.1 12.68 17.7 14.54 1.080 1.076 1.078 LINCOLN CONT'L. 460-A* 9.3 9.8 9.55 10.2 10.5 10.35 0.923 15.0 15.5 15.25 11.48 10.3 9.51 16.2 11.68 1.004 0.941 0.983 SIX-CAR AVERAGE RATIOS: CITY 1.080 HIGHWAY 1.056 55/45 1.071 * Radial Tires ** Bias Tires ------- 4.0 TEST DESIGN The test program was designed to produce data on the following fuel economy influences: « Dynamometer mpg vs. track mpg » Effects of tire type (radial vs. bias-belted) and tire pressure • Effects of air conditioner operation and air conditioner simulation • Effects of deviations from the standard EPA Highway Cycle • Carbon balance vs. volumetric fuel consumption measurement 4.1 Dynamometer MPG vs. Track MPG The same basic test cycles were run on the dyno and the track, and included: t The EPA urban driving schedule ("city cycle" or "LA-4") i • The EPA highway driving schedule • Steady-state cruises e Modified versions of the EPA highway schedule e Coastdowns from 60 to 5 mph Fuel flowmeters were used in the dyno tests to permit comparisons with the track tests on a common fuel measurement basis. Unfortunately, the same fuel flowmeter used to measure the fuel economy of a car tested on a dynamometer was not always used to measure fuel economy of the same car tested on the test track. Thus, any flowmeter to- flowmeter differences or biases due to calibration or other effects introduce additional variability or biases into the differences measured between dyno/track fuel economies. More will be discussed concerning flowmeter effects in Section 8.2. ------- ------- For all "A/C on" tests, the air conditioner temperature and blower controls were set for maximum cooling. In the dyno A/C "simulation" tests, the air conditioner was turned off and the dyno road load* at 50 mph increased 10% in accordance with EPA certification procedure. 4.4 Effects of Highway Test Modifications Five variations from the standard EPA highway test were investigated by means of the following: • Cold starting, denoted as CST • "Noisy" driving schedule, denoted as HNO o "Redistributed" driving schedule, denoted as HRE • "Smooth" driving schedule, denoted as HSM t 50 mph steady state cruise The cold start tests used the standard EPA nonurban driving schedule, so any observed mpg penalty would derive solely from vehicle warmup. In the Noisy cycle, the distribution of speeds is virtually the same as the standard cycle (so no mpg effects of this cycle were related to road load changes), but the undulations in the cycle are amplified so that acceleration rates due to cycle "noise" are essentially doubled. Any mpg penalty for this cycle would be a function of vehicle inertia. In the Redistributed cycle, the fine texture of the cycle is pre- served, but blocks of the trace are moved either up or down, giving a wider distribution of speeds (up to 73 mph and down to 18 mph, compared to 60 mph maximum and 28 mph minimum for the standard cycle). A fuel economy penalty seen with this cycle would stem from operation in the added lower—and higher—speed regimes, both of which are well-known detriments to fuel economy. In contrast to the above modifications, which increase the "busyness" of the cycle, the Smooth cycle consists simply of the standard cycle's initial acceleration, a constant 50 mph cruise, and the standard cycle's final deceleration; it is the smoothest possible variant of a 10-mile drive that begins and ends at idle and averages 48 mph. Calibrated power abortion unit (PALI) setting ------- ------- 5.0 TEST VEHICLES The vehicles tested in this program span a wide range of car sizes and types. The vehicles were 1976 model production cars, with a minimum of 2000 miles accumulated in routine service prior to the tests.* Summary descriptions of the vehicles with both dynamometer and track test data are given in Table 2; Appendix B gives more detailed configura- tion data on each vehicle. The vehicles involved in the different effects investigated in the test program are shown in Table 3. Exceptions: The Aspen Wagon and Impala had less than 2000 odometer miles at delivery, and were "aged" to 2000 miles using the EPA mileage accumulation procedure. 11 ------- Table 2 TEST VEHICLES MAKE/MODEL Honda Civic Datsun B-210 Ford Pinto AMC Pacer Ford Granada Dodge Aspen Wagon Chevrolet Impala Chevrolet Chevette ENGINE 91 CID CVCC 85 CID 140 CID 232 CID 250 CID 225 CID 350 CID 98 CID WEIGHT CLASS 2000 2250 3000 3500 4000 4000 5000 2250 TRANSMISSION 4-Speed Manual 4-Speed Manual 3-Speed Auto- matic 3-Speed Auto- matic 3-Speed Auto- matic 3-Speed Auto- matic 3-Speed Auto- matic 3-Speed Auto- matic AIR CONDITIONED No No No Yes Yes Yes Yes Yes 12 ------- Table 3 RELATIONSHIP BETWEEN EFFECTS INVESTIGATED AND TEST VEHICLES CAR Honda CVCC Datsun B-210 Ford Pinto AMC Pacer Ford Granada Dodge Aspen Wagon Chevrolet Impala Chevrolet Chevette DYNO (METER MPG) VS. TRACK No Radial , Bias Radial, Bias Bias Radial , Bias Radial , Bias Radial, Bias Radial RADIALS VS. BIAS-BELT Dyno Dyno, Track Dyno, Track Track Dyno, Track Dyno, Track Dyno, Track Track AIR CONDITIONING No No No Dyno, Track Dyno, Track Dyno, Track Dyno, Track Track CVS VS. METER (DYNO) Yes Yes Yes Yes Yes Yes Yes Yes TIRE WARMUP Dyno, Bias Dyno, Track Radial , Bias Track, Radial , Bias Dyno (Bias), Track (Radial, Bias) Dyno (Radial), Track (Radial, Bias) Dyno, Track Radial , Bias Dyno, Track Radial s No MOD. HIGHWAY CYCLES Dyno, Radial s Dyno, Track Radial s Dyno, Track Bias Dyno, (Bias) , Track (Radial, Bias) Dyno (Radial) Track (Radial , Bias) Dyno (Radial , Bias) Track (Radial) Dyno, Track Radials Track (Radials, Bias) FUEL FLOWMETER NO. DYNO/TRACK 1514 Unknown, 2099 1513, 2099, 1514 1472 1514 1513, 1514, Unknown Unknown, 1514 1513, 1514, 1358 Unknown Unknown, 1514, 1472 Unknown Unknown, 1514 Unknown, 1514 1472 Unknown 1472 ------- 6.0 TEST PROCEDURES At arrival, each test car was inspected, and tuning and condition of vacuum and EGR lines compared to manufacturers' specifications. Five of the cars required minor adjustments; none of the vehicles was found to be significantly out of specification. Following this incoming inspection, each vehicle was given a standard dyno FTP and HFET test series, using certification-type pre- conditioning and the certification city and highway procedures. These baseline tests were used as a go/no-go screening prior to committing the cars to the full series of dyno and track testing. Results of the base- line tests are shown in Table 4. The emissions column in Table 4 gives the highest value for each pollutant in any one baseline test, not the average values for all base- line tests. The only instance in which any pollutant exceeded the levels of the 1976 Federal Emission Standards* was in one Pacer test, where NOX was 5% high; average NOX for all of the baseline Pacer tests was within the Standard. All fuel economy values for the test cars were within 3% of certi- fication car test results. The Pinto yielded the largest shortfalls between test car mpg and certification car mpg; 7% city and 8% highway; nevertheless, the Pinto was accepted for testing in view of its admirable assault on the 1980 Emission Standards. Most of the dynamometer tests were performed on the same twin-roll water brake certification dynamometer, denoted #5 (some tests were conducted on twin-roll dynamometer denoted #207), using the same inertia weight and road load settings as each test car's certification couter- part. Vehicle speed measurements were taken from the reaXdyno roll. < The track tests were run on the 7.5 mile high-speed oval at Ohio's Transportation Research Center, using a 5th wheel for speed indication. HC = 1.5 g/m; CO = 15 g/m; NO =3.1 g/m 14 ------- Table 4 BASELINE TEST RESULTS VEHICLE Honda (Bias-Belt) Datsun (Bias-Belt) Pinto (Bias-Belt) Pacer (Bias-Belt, A/C Sim) Granada (Radial, A/C Sim) Aspen (Radial, A/C Sim) Impala (Radial , A/C Sim) MAXIMUM 1975 FTP EMISSIONS, gm/mi(a) HC 0.80 CO 4.88 NO 1 . 54 X HC 0.99 CO 8.97 NOX 2.46 HC 0.42 CO 2.51 NOX 1.79 HC 1.06 CO 11.84 NOX 3.27(b) HC 1.21 CO 3.72 NOX 1.46 HC 0.68 CO 3.03 NOX 2.54 HC 0.57 CO 12.57 NOX 2.50 City Hwy 55/45 City Hwy 55/45 City Hwy 55/45 City Hwy 55/45 City Hwy 55/45 City Hwy 55/45 City Hwy 55/45 CARBON BALANCE FUEL EC Test Car 29.9 41.5 34.2 27.7 39.5 32.0 21.0 29.0 24.0 17.8 21.6 19.4 16.5 18.9 17.5 17.4 22.8 19.4 12.3 18.0 14.3 )ONOMY, MPG Cert. Car 31.9 41.8 35.7 27.9 39.8 32.2 22.5 31.5 25.8 17.5 22.3 19.4 15.7 19.2 17.1 17.6 22.6 19.5 13.0 18.6 15.0 ^ Highest value obtained for each pollutant in any replicate test. (b) Average NO for all Pacer baseline tests was 2.95. /\ 15 ------- ------- 7.0 RESULTS OF FUEL ECONOMY TESTS Major test parameters are: Location (Dynamometer -No./Track) Vehicle Tire Type (Radial/Bias Belted) Tire Pressure(s) Air Conditioner Status (Off/On/Simulated*) Fuel Flow Meter Number Driving Cycle (CC/HH/HC/FTP/HST/CST/HNO/HRE/HSM - Steady State: 10/20/30/40/50/60/70/80 mph) Over urban driving cycles, CC/HH/HC/FTP, fuel economy values were recorded for the individual transient and stabilized segments, viz. BAG1 (cold transient), BAG2 (hot stabilized) and BAG3(hot transient), included in the cycle. The BAG1, BAG2, and BAGS fuel economies were considered the basic data, rather than the overall cycle composite fuel economies. As will be described in Section 8.3, an analysis of dynamometer and fuel flowmeter effects led to the conclusion that the two dynamometer test cells used were essentially equivalent and that certain fuel flowmeters could be validly aggregated after application of specified corrections in fuel consumption space. Tests which matched in all of the above parameters were then considered replicated, and sample mean fuel economy values were computed. In case of two or more replications, the coefficient of variation (unbiased estimate of standard deviation divided by the sample mean) was also computed. These aggregated results are presented in Appendix C. Included in the results presented are FTP and HH (i.e., hot-start urban cycle) fuel economies. These were derived from the individual bag results by application of the standard FTP formulas. FTP mpg = 1 r 0-21 i LBAGI mpgl f 0-52 ] [BAG2 mpgj 0.27 I BAG3 mpgl HH mpq = r o:52 i i [_BAG2 mpgj f 0.48 * BAG3 mpg * Dynamometer runs only. 17 ------- 8.0 ANALYSIS OF RESULTS 8.1 Use of Ratio Measure for Fuel Economy Comparisons Fuel economy differences between dyno and track runs (as well as between radial and bias-belted tires, air conditioning off and on, and other factor comparisons) were measured over a wide range of absolute fuel economy levels, reflecting the various test vehicles and driving sequences employed. It is desirable, therefore, to display fuel economy differences in a manner which most effectively unifies the observed effects throughout the test range of absolute fuel economy levels. The two alternatives frequently considered are based on an additive model and a multiplicative model, respectively. In the former the measure is the arithmetic difference in fuel economies; in the latter it is their ratio. Mathematically, if Ej and E2 are the two fuel economies being compared, these measures are defined as: and 2 P = Basically, the additive model is most appropriate when a given influential factor produces a change in fuel economy from E^ to E2 which tends to be independent of the magnitude of Ej; the multiplicative model is appropriate when the change tends to be proportional to E}. Actually, the use of fuel economy E (in mpg) as a measure of fuel efficiency is somewhat arbitrary. An equally meaningful variable is its inverse, fuel consumption C~ ( i n gpm) . Application of the additive and multiplicative models to the fuel consumption variable yields: AC = C2 - Cl C2 pc = c~ L L 18 ------- Note, now, that the assumption of a multiplicative model in E is fortuitously equivalent to a multiplicative model in C. By definition of C = 1/E, it is easily seen that PC = 1/PE On the other hand, suppose an additive model in E were assumed. One can then write A_ c r — — _ — A r r ~ AT r ? i ~ F "F ~ ~~?~F— - - A- • c.,1 ~ - A L ^ <- 1 tp t, 1 ? which indicates that constant small fuel economy differences imply fuel consumption differences proportional to the square of fuel consumption level. By analogous reasoning, an additive model in C implies fuel economy differences proportional to the square of fuel economy level. Inasmuch as the same information is conveyed by A£ or pp_, either measure may be selected. However, the above considerations suggest that P£ may be more physically meaningful. Another argument for choosing PE is that, under the reasonable assumption of constant measurement error coefficient of variation1* p£ would have constant error variance, whereas AE would not. It is further noted that the ratio measure was employed in the previous dynamometer/track fuel economy study by EPA1 and hence its use here would also facilitate comparison of results. A final consideration is how well the ratio measure fits the observed data. Figure 1 is a plot of dynamometer fuel economy to track fuel economy under matched experimental conditions (same car, same tires, same driving sequence, etc.). Note that a ratio regression line is reasonably compatible with the data. 8.2 Comparison of Carbon Balance and Volumetric Measurement Past EPA studies2'3 have noted systematic differences between carbon balance and volumetric method of fuel economy determination. Inasmuch as the FTP and HFET dynamometer procedures specify use of the carbon balance method, whereas in track runs practical considerations dictate reliance on a fuel flowmeter, any realistic comparison of dynamometer to track fuel economies must include possible systematic effects of using different measurement techniques. 19 ------- pr= 1.108 for this example 24 32 TRACK FUEL ECONOMY (mpg) FIGURE 1. Relationship Between Dynamometer and Track Fuel Economies 20 ------- Since all dynamometer runs in the test program were set up to measure both carbon balance and volumetric fuel consumptions, it is technically feasible to calculate the carbon balance to meter systematic difference as a separate effect. All subsequent analyses could then be simplified to direct comparison of metered fuel economies in both dynamometer and track runs. However, an additional complication which developed in the experi- mental program was the use of several different fuel flowmeters with potentially significant systematic differences amongst themselves. Three of the meters were employed in both dynamometer and track runs and can therefore be related to carbon balance measurements as a reference. Unfortunately, three other meters were used only in track runs and are therefore not accessible to analyses for systematic differences. There follows below the results of a statistical analysis of systematic carbon balance to volumetric measurement differences. Dynamometer runs were identified as having been performed on either of two dynamometers (#5 or #207) and as using one of three fuel flowmeters (#1513, #1514, or #2099); in a significant number of instances the meter identification was missing. The runs were grouped into eight separate classes (2 dynamometer x 4 meters) to allow for the possibility of both dynamometer test cell and fuel flowmeter effects. The distribution into the eight classes was very uneven, and two classes were empty. Within each class, replicated runs (same car, tires, air conditioning status, driving sequence, etc.) were averaged. The occupancy of the eight classes, by numbers of individual runs and numbers after averaging, is shown in Table 5. Table 5. NUMBERS OF INDIVIDUAL/AVERAGED DYNAMOMETER RUNS DYNO\NO . NO. \\ 5 207 1513 0 12/11 1514 95/58 4/2 2099 21/21 0 UNKNOWN 77/40 7/4 21 ------- For each class two alternative linear models were considered: AE = E - E = a + bE cm m AC=C -C =r+sC cm m where E denotes fuel economy (mpg), C denotes fuel consumption (gpm) and subscripts c and m refer to carbon balance measurements and volumetric measurements, respectively. Weighted least squares regressions were then carried out to estimate parameters a, b, r, and s. The weighting was based on the assumption of a constant coefficient of variation for the difference between carbon balance and meter readings (relative to the meter reading as a base) over all individual runs within a class, and statistical independence of replicated runs. Details of the regression analyses are given in Appendix D. Figures 2 and 3 present the regression lines obtained for the linear fuel consumption models and linear fuel economy models, respectively. The lines are extended to cover only the data range, and the ± la ranges for midpoint estimates are shown. For comparison purposes the two alternative regression lines obtained in a recent EPA study are also reproduced in Figure 2. It is concluded from an examination of the results, including residual coefficients of variation (which range from 1 to 3.5%), that: (1) the linear fuel consumption model provides a somewhat better fit to the data than the linear fuel economy model; (2) there is no appreciable effect associated with the use of two different dynamometers; (3) all classes including the earlier EPA study2'3- showed remarkably similar slopes in the variation of measured carbon balance to meter differences as a function of absolute fuel consumption; and (4) there are significant differences in intercept between meters 1513 and 1514 and between meters 2099 and 1514. It was accordingly decided to adjust meter 1513 and meter 2099 readings so as to be consistent with meter 1514 readings. The unknown meter class (presumably a mixture of meters 1513, 1514, and 2099 readings) was sufficiently similar to meter 1514 as not to require any adjustment. The adjustment formulas developed were: E adj. I- where K = -0.00041 for Meter 1513 = +0.00063 fpr Meter 2099 22 ------- O.OOlf \ -f- 0.04 \ 0.05— 0.06 0.07 Q-.08 NxVOLUMETRIC FUEL CONSUMPTION (CM) (gpm) \ \ \ \ 0:01 -0.001 -0.002 -0.003 M V -„ \ \ \ EPA Regression Lines3 \3 iGeneral Linear Model Constrained through Origin : J \ ; KEY: A B C D E F DYNO METER NO. NO. 5 2099 207 Unknown 5 1514 5 Unknown 207 1514 207 1513 NO. OF REPLICATED GROUPS 21 4 58 40 2 11 FIGURE 2. Regression Lines for Differences Between Carbon Balance and Volumetric Fuel Consumption 23 ------- l.D 1.0 O 0.5 -0.5 -1.0 10 40 VOLUMETRIC FUEL ECONOMY (EM) (mpg) KEY: A B C D E F DYNO NO. 5 207 5 5 207 207 METER NO. 2099 Unknown 1514 Unknown 1514 1513 NO. OF REPLICATED GROUPS 21 4 58 40 2 11 45 FIGURE 3. Regression Lines for Difference Between Carbon Balance and Volumetric Fuel Economy 24 ------- These adjustments were also made in all track runs using meters 1513 or 2099. Unfortunately, as previously noted, three other meters were used on many of the track runs. The calibration of these meters relative to 1514 is unknown. Inasmuch as fuel economy ratios involving these "uncalibrated" meters could involve an error of appreciable magnitude just resulting from meter discrepancy, it was decided that ratios would only be computed where both numerator and denominator readings are from meter 1514 or adjusted to meter 1514. The question as to which of the measurements are most accurate in an absolute sense, however, cannot be determined from this investigation. The fact that the carbon balance method is indirect whereas the fuel flowmeters measure volume directly by positive displacement of an essentially incompressible fluid suggests that the volumetric method is apt to be more accurate. However, the observed meter- to- me ter discrepancies certainly argue against placing any more confidence in the meter data actually obtained than in the carbon balance results. These considerations further support the decision to express all ratios on the basis of a common meter reference. If one wished to proceed further and attempt to estimate real dyno- to-track fuel economy ratios where dyno fuel economy is measured by the carbon balance method, then one could multiply the ratios presented later in this report by the ratio of measured carbon balance to meter 1514 derivable from Figure 2. The latter is seen to vary from about 1.04 at fuel consumption levels of 0.08 gpm (12.5 mpg) to about 1.015 at fuel consumption levels of 0.025 gpm (40 mpg). However, it should be kept in mind that the composite ratios so derived are meaningful only in the context of meter 1514 (or one with similar calibration) employed in measuring track fuel economy. The composite ratios would change if the track meter had substantially different calibration. In the final analysis, proper resolution of this whole problem requires the applica- tion of a fuel measurement technique of validated high accuracy against which all other measurements could be compared. 25 ------- 8.3 Estimates of Testr-to-Test Variability The presence of replicated runs in the data base permits estimation of the basic variability from test to test in volumetric fuel economy measurement. Such estimates are necessary for statistical analysis of significant effects. The assumed model is that of a constant coefficient of variation (COV), i.e., standard deviation divided by mean fuel economy over the range of measured fuel economies.** However, one must allow for the possibility of different COV's over track and dyno runs and also over various driving sequences. The latter were partially aggregated into BAG1/BAG3, BAG2, HST/CST, HNO/HRE, HSM, and CRUISE classes, based on the judgment that hot vs. cold start has no impact on measure- ment error, similarity of noisy and redistributed highway sequences, and insufficient numbers of CRUISE replications at individual speeds. Table 6 presents estimated COV's for each of the indicated classes, determined as a weighted average of estimates from individual replicate groups. As a result of the meter adjustments described in Section 8.2, all dynamometers were rendered comparable; however, track runs with uncalibrated meters additionally had to agree in meter number to qualify as replicates. The number of degrees of freedom for estimation is given by d.f. = £(n.j - 1) where n-j is the number of replications in the i replicate group and summation is over all replicate groups in a class. Analysis revealed that differences among BAG2, HST/CST, HNO/HRE, HSM, and CRUISE estimates of (COV)2 were not statistically signifi- cant. Accordingly, these classes were pooled. Differences between BAG1/BAG3 and the pooled results were statistically significant. We are thus left with distinct estimates of (COV)2 for four cases: Dyno- BAG1/BAG3, Dyno-Other, Track-BAGl/BAG3, Track-Other. Fortuitously, these were found to be well-approximated by DYNO TRACK BAG1/BAG3 OTHER 2 (COV)2 (COV)2 4 (COV)2 2 (COV)2 26 ------- Table 6 ESTIMATES OF TEST-TO-TEST SQUARED COEFFICIENT OF VARIATION DRIVING SEQUENCE BAG1/BAG3 BAG2 HST/CST HNO/HRE HSM CRUISE BAG2/HWY/CRUISE** DYNAMOMETER (COV)2 (%)2 7.34 2.25 3.69 3.42 4.02 4.97 3.53 d.f.* 56 32 32 30 15 24 133 TRACK (COV)2 (%)2 14.36 7.78 8.76 2.37 5.24 7.56 7.13 d.f.* 64 73 44 30 12 106 265 * Number of degrees-of-freedom for estimation. ** Pooling of BAG2, HST/CST, HNO/HRE, HSM, and CRUISE. 27 ------- or in terms of COV by BAGI/BAG3 OTHER DYNO TRACK /T(COV)0 (COV)Q 2 (COV)Q /2~(COV)0 where (COV)Q - 1.9%. To investigate the consistency of these dynamometer test-to-test variability estimates with previously obtained results, we note first that the COV estimate for FTP fuel economy (0.21 BAG1 + 0.12 BAG2 + 0.27 BAG3) derived from the above is [(0.21)2 • 2 (COV)§ + (0.52)2 • (COV)g + (0.27) - 2 (COV)£] = 1.35%. The HFET (Highway) fuel economy COV is, of course, just 1.9%. Reference 4 indicates COV's reported in the literature ranging from 0.75 to 4.8% and also includes an analysis of recent EPA tests on thirty-one automobiles5 which yielded FTP and HFET fuel economy COV's of 1.5% and 1.9%, respectively. COV estimates based on data from the present program are therefore very much in line with other estimates. In subsequent sections, ratios of sample mean fuel economies are calculated. The above results for test-to-test coefficient of variation are used to estimate the standard error of the mpg ratios as follows: mpg. P = where mpg^ and mpgo are sample means of Nj and N2 measurements, respectively, and the squared coefficient of variation of single test results are (COV)f and (COV)2, respectively. Then the standard error of the estimate p is given by: (s.e.)p = /(COVjj2 (COV) For example, if mpg is dynamometer BAG2 value with 3 replications and inpgT is a track BAG2 value with 4 replications then 2r> O ------- (s.e.)p = (COV)2 2 (COV) '0 - = 0.91 (COV)Q = 0.015. The standard error for FTP and HH ratios derived from replicated BAG measurements is somewhat more involved. For example, if dynamometer FTP is derived from an N^-replicate BAGjl value, an N12-replicate BAG2 value, and an N13-replicate BAGS value, the standard error for p = FTP (dyno)/FTP (track) is (s.e.)p = (0.21)2 2 (COV)2 (0.52)2 (COV)2 (0.27)2 2 (COV)2 11 12 13 (0.21)2 4 (COV)2 (0.52)2 2 (COV)2 (0.27)2 4 (COV)2 21 22 N 23 /0.0882 , 0.2704 . 0.0882 0.1764 0.5408 0.1764 / ri + r, + —r. + ——r, + r, + n 11 12 13 21 22 23 With only one replication for each BAG, the dyno/track FTP ratio standard error would become (s.e.)p = 0.022. The modest numbers of replications appearing in the data generally result in ratio standard errors in the range of 0.01 to 0.015, i.e., 1 to 1.5% 29 ------- 8.4 Dynamometer/Track Effects—Dynamometer Measured Fuel Economy Compared to Track Measured Fuel Economy The prime focus of this program is to quantify when possible the magnitudes of the differences between fuel economy as measured on a dynamometer and on a test track. As previously discussed, the parameter chosen to quantify the dyno/track effect is the ratio of the fuel economy as measured by fuel flowmeter on a dynamometer, to fuel economy as measured by fuel flowmeter on a test track. These ratios have been computed where meter 1514 (or a meter that could be corrected to #1514) was used for both the dynamometer and track measurements (i.e., meter 1514 was used as the basis to which all the meters were corrected where possible). Tables 7 through 10 present the calculated ratios with their standard errors for the four tire-type/air-conditioning configurations: radial tire/air off, radial tire/air on, bias tire/air off, and bias tire/ air on. Ratios were calculated for the above four groups to consider possible effects due to either tire type and/or air conditioning. Once the ratios are computed by group, an analysis of variance may be used to test whether significant differences exist between the ratios of any two groups. For instance, it is reasonable to expect that the dynamometer- to-track effect (i.e., the ratio) should be the same when the vehicle is tested with air conditioning on and air conditioning off. To test our hypothesis that the ratios between two groups are the same, we assume a model of the form: y.. =y + b. + t. +e.. ij i i ij where: y.. are the computed ratios for each i vehicle in the j 1J group (i.e., air or no air conditioning), y is the mean ratio over all vehicles and groups, b.j is the deviation from the mean ratio due to each itn vehicle, t.: is the deviation from the mean ratio due to each jth group, and e.. is the random component of error due to both measurement 1J and test variance for the ith vehicle in the jth group. In the above model the e-jj are assumed independent. By a weighted analysis of variance, we may test for vehicle-to-vehicle differences in the ratios (b. £ b) and group-to-group differences in the ratios (t. £ t). A complete I vJ 30 ------- Table 7 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Radial, Air Off, Windows Up, Meter 1514 or Corrected) BAG1 BAG2 BAG 3 FTP HH HST CST HND HRE HSM 10 20 30 40 50 60 PINTO 0.992 ± 0.033 1.055 ± 0.018 1.103 ± 0.029 1.051 ± 0.014 1.078 ± 0.017 1.063 ± 0.022 0.911 ± 0.030 1.023 ± 0.030 1.040 ± 0.030 1.074 ± 0.030 1.045 ± 0.030 1.027 ± 0.030 HONDA* 1.122 ± 0.029 1.111 ± 0.015 1.115 ± 0.022 1.114 ± 0.011 1.113 ± 0.013 1.118 ± 0.016 1.100 ± 0.030 1.159 ± 0.022 1.170 ± 0.022 1.084 ± 0.029 ASPEN 1.100 ± 0.029 1.100 ± 0.016 1.066 ± 0.027 1.092 ± 0.012 1.080 ± 0.015 1.066 ± 0.016 1.053 ± 0.033 1.053 ± 0.019 1.016 ± 0.016 1.053 ± 0.017 1.011 ± 0.033 0.991 ± 0.033 0.942 ± 0.033 1.021 ± 0.033 1.016 ± 0.033 0.993 ± 0.033 * Combined meter unknown and 2099 corrected on track. 31 ------- Table 8 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Bias, Air Off, Windows Up, Meter 1514 or Corrected) BAG1 BAG 2 BAG 3 FTP HH HST CST HND HRE HSM 10 20 30 40 50 60 PINTO 1.051 ± 0.042 1.113 ± 0.018 1.152 ± 0.020 1.106 ± 0.015 1.132 ± 0.017 1.127 + 0.022 1.105 ± 0.019 1.114 ± 0.019 1.060 ± 0.022 HONDA 1.191 ± 0.031 1.076 ± 0.018 1.062 ± 0.025 1.097 ± 0.013 1.070 ± 0.015 1.148 ± 0.019 0.712 ± 0.027 0.919 ± 0.027 1.350 ± 0.027 1.350 ± 0.027 1.210 ± 0.027 PACER 1.065 ± 0.030 1.016 ± 0.033 1.040 ± 0.026 1.116 ± 0.029 ASPEN 1.179 ± 0.042 1.131 ± 0.016 1.120 ± 0.025 1.140 ± 0.014 1.126 ± 0.014 1.086 ± 0.021 0.825 ± 0.027 1.117 ± 0.027 1.035 ± 0.027 1.099 ± 0.027 1.118 ± 0.027 1.066 ± 0.027 32 ------- Table 9 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Radial, Air On, Windows Up, Meter 1514 or Corrected) BAG1 BAG2 BAG3 FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 ASPEN 1.111 ± 1.090 ± 1.015 ± 1.076 ± 1.052 ± 1.044 ± 0.870 ± 0.990 ± 0.950 ± 1.018 ± 1.029 ± 0.934 ± 0.033 0.019 0.033 0.015 0.019 0.019 0.027 0.027 0.027 0.027 0.027 0.027 33 ------- Table 10 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Bias, Air On, Windows Up, Meter 1514 or Corrected) BA61 BAG2 BAGS FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 PACER 1.019 ± 0.033 1.083 ± 0.016 1.049 ± 0.029 1.057 ± 0.013 1.066 ± 0.016 1.150 ± 0.025 0.884 ± 0.033 0.967 ± 0.033 1.030 ± 0.033 1.038 ± 0.033 1.029 ± 0.033 ASPEN 1.216 ± 0.027 1.165 ± 0.038 1.193 ± 0.023 1.035 ± 0.021 34 ------- derivation and explanation of this analysis is presented in Appendix E. Application of the above analysis of variance indicates that there is no significant difference in the computed ratios (dynamometer fuel economy to track fuel economy) for vehicles with air conditioning on and for vehicles with air conditioning off. There is however, a significant car to car effect among the calculated ratios. The analysis of variance results for the FTP and HST driving cycles is presented in Table 11. In Table 11 the quantities S/E and T/E are presented with the estimate of y and SQZ. The quantity S is the reduction in mean square error associated with fitting b-j, the quantity T is the reduction in mean square error associated with fitting tj, and the quantity SQZ is an externally derived mean squared error (with a large number of degrees of freedom) which provides an estimate for the internal mean squared error E. The ratios S/E and T/E were then compared with F distributions of equivalent degrees of freedom at a selected significance level (i.e., 0.05). In all instances presented in Table 11 we reject the hypothesis that vehicle effects are all the same (b-j =b) and accept the hypothesis that a/c on and off effects are the same (tj 5 t). Thus we may combine the ratios computed with air conditioning on with the ratios computed with air conditioning off, but we may not combine the ratios computed for car A with the ratios computed for car B. The ratios are combined by inverse weighting by their standard errors for air off and air on and are presented in Tables 12 and 13 for vehicles equipped with radial and bias tires, respectively. Vehicle-to-vehicle differences within each tire type group are evident. In addition, each vehicle equipped with radial tires appears to have a different ratio when equipped with bias tires. Fuel economy differences due to tire configuration effects are discussed in the next section. 35 ------- Table 11 ANALYSIS OF VARIANCE RESULTS FOR VEHICLES WITH AND WITHOUT AIR CONDITIONING FOR SELECTED DRIVING SEQUENCES VEHICLE CONFIGURATION HQ: b. »b Bias Tires Radial Tires V V Bias Tires Radial Tires DRIVING SEQUENCE FTP y = 1-087 SQ2 = 0.46385 d.f. = 4 S/E = 6.25* d.f. = 4 T/E = 0.68 HH y - 1.103 SQ2 = 0.8358 d.f. = 6 S/E = 9.96* d.f. = 6 T/E = 0.08 HST y = 1.108 SQ2 = 1.3365 d.f. = 6 S/E = 5.0* y = 1.076 SQ2 = 0.9053 d.f. = 4 S/E = 3.18* d.f. = 6 T/E = 0.73 d.f. = 4 T/E = 1.30 * Significant at 0.05 level. 36 ------- Table 12 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Radial, Air On + Air Off, Windows Up, Meter 1514 or Corrected) BAG1 BAG2 BAGS FTP HH HST CST HND HRE HSM 10 20 30 40 50 60 PINTO 0.992 ± 0.033 1.055 ± 0.018 1.103 ± 0.029 1.051 ± 0.014 1.078 ± 0.017 1.063 ± 0.022 0.911 ± 0.030 1.023 ± 0.030 1.040 ± 0.030 1.074 ± 0.030 1.045 ± 0.030 1.027 ± 0.030 HONDA 1.122 ± 0.029 1.111 ± 0.014 1.115 ± 0.022 1.114 ± 0.011 1.113 ± 0.013 1.118 ± 0.016 1.100 ± 0.030 1.159 ± 0.022 1.170 ± 0.022 1.084 ± 0.029 ASPEN 1.105 ± 0.022 1.096 ± 0.012 1.046 ± 0.021 1.086 ± 0.010 1.069 ± 0.012 1.056 ± 0.012 1.053 ± 0.033 1.053 ± 0.019 1.016 ± 0.016 1.053 ± 0.017 0.926 ± 0.021 0.990 ± 0.021 0. 950 ± 0.021 1.019 ± 0.021 1.024 ± 0.021 0.958 ± 0.021 37 ------- Table 13 RATIO ± 1 STANDARD ERROR OF DYNAMOMETER MPG TO TRACK MPG (Bias, Air On + Air Off, Windows Up, Meter 1514 or Corrected) BAG1 BAG 2 BAGS FTP HH HST CST HND HRE HSM 10 20 30 40 50 60 PINTO 1.051 ± 0.042 1.113 ± 0.018 1.152 ± 0.029 1.106 ± 0.015 1.132 ± 0.017 1.127 ± 0.022 1.105 ± 0.019 1.114 ± 0.019 1.060 ± 0.022 HONDA 1.191 ± 0.031 1.076 ± 0.018 1.062 ± 0.025 1.097 ± 0.013 •1.070 ± 0.015 1.148 ± 0.019 0.712 ± 0.027 0.919 ± 0.027 1.350 ± 0.027 1.350 ± 0.027 1.320 ± 0.027 PACER 1.019 ± 0.033 1.079 ± 0.014 1.035 ± 0.022 1.057 ± 0.013 1.059 ± 0.014 1.136 ± 0.019 0.884 ± 0.033 0.967 ± 0.033 1.030 ± 0.033 1.038 ± 0.033 1.019 ± 0.033 ASPEN 1.179 ± 0.042 1.154 ± 0.014 1.133 ± 0.021 1.140 ± 0.014 L145 ± 0.012 1.060 ± 0.015 0.825 ± 0.027 1.117 ± 0.027 1.035 ± 0.027 1.099 ± 0.027 1.118 ± 0.027 1.066 ± 0.027 38 ------- 8.5 Tire Effects—Fuel Economy Measured with Radial Tires Compared to Fuel Economy Measured with Bias Tires Testing of the vehicles with both bias belted and radial tires on the dynamometer and the test track permits a comparison of the effect of tire type on fuel economy. The ratio of the meter measured fuel economy of a vehicle with radial tires to the meter measured fuel economy of the same vehicle with bias belted tires is computed and presented in Tables 14 and 15 for track and dynamometer runs, respectively. Before the combined ratios in Tables 14 and 15 were computed, they were computed separately for the conditions of air conditioning on and off. Since no significant air conditioning effect was detected in Section 8.4 and since there is no apparent basis for considering a tire type air conditioning interaction effect,.the ratios (air on and off) were combined. Also note in Tables 14 and 15 that since the same fuel meter was often used to test the vehicle with radial and with bias tires, more ratio calculations are possible than were possible for dynamometer- to-track ratio calculations. In general, we note that the radial-to-bias ratio is dependent on the driving cycle and can be less than or greater than one. Ratios computed from track tests are generally greater than one and tend to support the contention that radial tires achieve somewhat better fuel economy (0 to 4% better for highway cycle) than bias tires. For comparisons on the dynamometer, ratios are generally lower than one, implying that dynamometer testing—instead of simulating the on-road fuel efficiency of radial tires in comparison to bias belted tires, generally shows radial tires at a relative disadvantage. 39 ------- Table 14 RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH RADIAL TIRES TO FUEL ECONOMY MEASURED WITH BIAS TIRES FOR DYNAMOMETER TESTS BAG1 BAG 2 BAG 3 FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 PINTO 0.975 ± 0.027 0.964 ± 0.016 0.965 ± 0.022 0.967 ± 0.012 0.964 ± 0.014 0.980 ± 0.015 0.952 ± 0.023 0.961 ± 0.023 0.917 ± 0.023 0.990 ± 0.023 0.980 ± 0.023 0.967 ± 0.023 HONDA 0.997 ± 0.024 1.029 + 0.013 1.030 ± 0.017 1.022 ± 0.010 1.034 ± 0.011 0.985 ± 0.017 0.984 ± 0.019 0.987 ± 0.023 0.989 ± 0.023 0.990 ± 0.023 0.986 ± 0.023 0.988 ± 0.023 0.987 ± 0.023 DATSUN 0.967 ± 0.024 0.985 + 0.014 0.994 ± 0.019 0.984 ± 0.010 0.990 ± 0.012 0.975 ± 0.014 0.969 ± 0.023 1.008 ± 0.017 1.116 ± 0.017 0.962 ± 0.019 0.958 ± 0.019 0.953 ± 0.019 0.958 ± 0.019 1.000 ± 0.019 0.968 ± 0.019 ASPEN* 0.999 ± 0.021 0.977 ± 0.013 0.989 ± 0.018 0.992 ± 0.009 0.983 ± 0.010 1.038 ± 0.012 1.002 ± 0.027 0.989 ± 0.016 1.002 ± 0.016 1.198 ± 0.027 0.997 ± 0.017 0.997 ± 0.027 0.977 ± 0.027 0.988 ± 0.027 0.983 ± 0.027 IMPALA 0.961 ± 0.027 1.014 + 0.016 0.988 ± 0.023 0.996 ± 0.012 1.001 ± 0.014 0.982 ± 0.014 * Combined ratios for air on and air off. ------- Table 15 RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH RADIAL TIRES TO FUEL ECONOMY MEASURED WITH BIAS TIRES FOR TRACK TESTS BAG1 BAG2 BAGS FTP HH HC HST CST UNO HRE HSM 10 20 30 40 50 60 70 BO PINTO 1.032 ± 0.047 1.017 ± 0.020 1.008 ± 0.035 1.018 ± 0.017 1.013 ± 0.019 — 1.039 ± 0.027 0.978 ± 0.033 — — — — — — — — — — HONDA 1,057 ± 0.035 0.997 ± 0.019 0.982 ± 0.028 1.006 ± 0.014 0.994 ± 0.017 — 1.012 ± 0.018 — 0.992 ± 0.027 1.009 ± 0.027 1.029 ± 0.033 1.070 ± 0.027 0.955 ± 0.027 1.088 ± 0.027 1.064 ± 0.027 1.028 ± 0.027 — — — DATSUN 1.093 ± 0.042 1.040 ± 0.016 1.053 ± 0.028 1.055 ± 0.014 1.046 ± 0.016 — 1.034 ± 0.019 — — — — 0.998 ± 0.027 1.009 ± 0.027 1.030 ± 0.027 1.033 ± 0.027 1.035 ± 0.027 1.020 ± 0.027 1.011 ± 0.027 1.027 ± 0.027 CHEVETTE 1.028 ± 0.038 1.016 ± 0.022 1.060 ± 0.030 1.030 ± 0.016 1.037 ± 0.018 — 1.022 ± 0.029 — 0.995 ± 0.027 1.019 ± 0.027 PACER* — 1.051 ± 0.033 0.970 ± 0.047 — 1.015 ± 0.028 1.009 ± 0.028 0.999 ± 0.038 1.025 ± 0.033 — — 1.012 ± 0.027] — 1.073 ± 0.027 1.108 ± 0.027 1.054 ± 0.027 1.013 ± 0.033 0.988 ± 0.027 1.064 ± 0.027 — — — — — — — — — ASPEN** 1.107 ± 0.044 1.029 ± 0.013 1.066 ± 0.023 1.057 ± 0.015 1.048 ± 0.013 — 1.044 ± 0.015 — — — - — 1.053 ± 0.021 1.068 ± 0.021 1.075 ± 0.021 1.058 ± 0.021 1.073 ± 0.021 1.058 ± 0.021 — — IMPALA** 1.100 ± 0.025 1.075 ± 0.011 1.071 ± 0.022 1.080 ± 0.010 1.075 ± 0.012 — 1.030 ± 0.018 — — — — 0.892 ± 0.028 1.038 ± 0.023 1.040 ± 0.023 1.014 ± 0.023 1.030 ± 0.023 1.007 ± 0.023 1.027 ± 0.023 1.032 ± 0.023 GRANADA 0.930 ± 0.038 0.986 ± 0.016 0.977 ± 0.023 0.970 ± 0.013 0.980 ± 0.013 — 1.030 ± 0.019 — — — — 1.103 ± 0.038 1.036 ± 0.033 1.009 ± 0.033 1.017 ± 0.036 1.014 ± 0.036 1.018 ± 0.036 1.025 ± 0.036 0.999 ± 0.036 * Meter 1358 data for radial only not used; ** Combined ratios with air on and off ------- 8.6 Cold Tire Warm-Up Effects In order to assess the potential influence of tire warm-up on fuel economy, comparable hot start LA-4 cycles were run using hot stabilized tires (HH) and cold tires (HC). These tests were conducted on the Aspen, Datsun, and Granada. Both the HC and HH fuel economies are computed by harmonically combining the fuel economies measured from BAGS2 and 3. In all cases tested, there were no significant differences either between HC and HH tests or between BAGS tests run with hot tires and BAGS tests run with cold tires. BAGS fuel economies were compared because these were the first segments of the HC and HH cycles and any fuel economy differences due to tire temperature should be greatest over the BAGS segment. Table 16 presents the ratios of HC to HH BAGS fuel economies as measured on the test track and dynamometer with either bias belted or radial ply tires. Comparisons between hot and cold tire fuel economies were made only where the same meter was used for measurement. In none of the individual cases, or combined groups, are the ratios significantly different from 1.00. 42 ------- Table 16. RATIOS OF BAGS FUEL ECONOMY WITH COLD TIRES TO BAGS FUEL ECONOMY WITH HOT STABILIZED TIRES AS MEASURED VS. USING BIAS OR RADIAL TIRES IN TRACK OR DYNAMOMETER TESTS ^^tEST LOCATION TIRE TYPE VEHICLE Aspen Datsun Granada Honda WEIGHTED MEAN (By Facility & Tire Type) WEIGHTED MEAN (By Facility) TRACK BIAS N* 2/2 1/2 2/3 Ratio ± 1 S.E.** 1.033 ± 0.038 0.992 ± 0.047 1.003 ± 0.035 — RADIAL N* 1/2 1/4 1/1 Ratio ± 1 S.E.** 0.951 ± 0.047 0.995 ± 0.042 1.072 ± 0.054 — 1.011 ± 0.023 1.000 ± 0.027 1.006 ± 0.018 DYNAMOMETER BIAS N* 3/1 Ratio ± 1 S.E.** — — 0.953 ± 0.031 RADIAL N* 2/2 Ratio ± 1 S.E.** — 0.977 ± 0.027 — — 0.953 ± 0.031 0.977 ± 0.027 0.967 ± 0.020 CO * Number of HC BAGS runs/number of HH BAGS runs. ** Standard errors based on COV estimated for test-to-test variability of BAG1/BAG3 runs on track and dynamometer derived in Section 8.3 ------- 8.7 Air Conditioning Effects Ratios of the meter-measured fuel economy with air conditioning off to the meter-measured fuel economy with air conditioning on have been computed for both dynamometer and track measurements separately. The results are presented in Tables 17 through 20 for the four groups: radials on track, radials on dynamometer, bias on track and bias on dynamometer. A subjective analysis of variance may be conducted by inspection of the ratios as recompiled in Table 21 for the four groups of conditions described. Notice that for each of the driving cycles presented, the four ratios for each vehicle do not appear to have any systematic pattern and may be collapsed into one ratio by weighted averaging (proportional to the inverse square of the standard error of each of the four group ratios). The recomputed ratios of fuel economy measured with air conditioning off to fuel economy measured with air conditioning on over all dynamometer, track, radial and bias tire configurations are presented in Table 22. It may be noted in Table 22 that a reduction is achieved in standard error for the weighted ratios as compared to the standard error for the individual configuration unweighted ratios, and that an apparently significant vehicle- to-vehicle difference in ratios remains. These ratios indicate decreases in fuel economy due to air conditioning ranging from 8 to 17% over the urban cycle and 5 to 12% over the highway cycle. The air conditioning effect in Table 22 appears to be inversely related to vehicle speed for the steady-state runs. That is, the ratios (converted to percent differences) calculated for each of the steady-state speeds indicated in the table decrease from about 16% at 10 mph to about 5% at 80 mph. 44 ------- Table 17. RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASUREMENT WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH AIR CONDITIONING ON FOR TRACK MEASUREMENTS OF VEHICLES WITH RADIAL TIRES en BAG1 BAG2 BAG3 FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 70 80 GRANADA* 1.150 ± 0.038 1.181 ± 0.016 1.192 ± 0.025 1.176 ± 0.013 1.186 ± 0.014 1.112 ± 0.015 — --- — — 1.164 ± 0.033 1.187 ± 0.033 1.131 ± 0.033 1.131 ± 0.033 1.102 ± 0.033 1.090 ± 0.033 1.111 ± 0.033 1.014 ± 0.033 CHEVETTE** 1.081 ± 0.038 1.098 ± 0.022 1.129 ± 0.030 1.101 ± 0.016 1.113 ± 0.018 1.050 ± 0.022 — — — — — 1.139 ± 0.027 1.119 ± 0.027 1.081 ± 0.027 1.033 ± 0.033 0.995 ± 0.027 1.029 ± 0.027 — PACER*** 1.044 ± 0.047 1.034 ± 0.020 1.103 ± 0.038 1.055 ± 0.018 1.064 ± 0.021 1.091 ± 0.038 — 1.070 ± 0.027 1.049 ± 0.027 1.086 ± 0.033 — 1.180 ± 0.027 1.095 ± 0.027 1.051 ± 0.027 1.058 ± 0.027 1.042 ± 0.027 1.001 ± 0.027 1.055 ± 0.027 ASPEN**** 1.080 ± 0.035 1.108 ± 0.018 1.040 ± 0.035 1.084 ± 0.015 1.074 ± 0.019 1.062 ± 0.021 — — — — 1.031 ± 0.033 1.163 ± 0.033 1.123 ± 0.033 1.063 ± 0.033 1.082 ± 0.033 1.052 ± 0.033 — — 1 IMPALA** 1.056 ± 0.038 1.110 ± 0.017 1.083 ± 0.032 1.091 ± 0.015 1.097 ± 0.018 1.043 ± 0.025 — --- — — — 1.206 ± 0.027 1.153 ± 0.027 1.111 ± 0.027 1.069 ± 0.027 1.100 ± 0.027 1.063 ± 0.027 1.056 ± 0.027 * Meter 1514 + Unknown *** Meter 1358 ** Meter 1472 **** Meter 1514 ------- Table 18. RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH AIR CONDITIONING ON FOR TRACK MEASUREMENTS OF VEHICLES WITH BIAS TIRES BAG1 BAG 2 BAGS FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 70 80 GRANADA* 1.103 ± 0.038 1.187 ± 0.016 1.148 ± 0.023 1.157 ± 0.013 1.169 ± 0.013 1.117 ± 0.022 — — — — — — — 1.134 ± 0.033 1.157 ± 0.033 1.119 ± 0.033 1.140 ± 0.033 1.019 ± 0.033 PACER* — 1.154 ± 0.028 1.154 ± 0.044 — 1.154 ± 0.025 1.154 ± 0.031 — — — — — — — — — — — — ASPEN** — 1.100 ± 0.022 1.045 ± 0.033 — 1.075 ± 0.020 1.062 ± 0.022 — — — — 1.172 ± 0.027 1.142 ± 0.027 1.125 ± 0.027 1.073 ± 0.027 1.059 ± 0.027 1.058 ± 0.027 — — IMPALA*** 1.028 ± 0.031 1.080 ± 0.016 1.068 ± 0.035 1.066 ± 0.015 1.074 ± 0.019 1.059 ± 0.031 — — — — 1.199 ± 0.038 1.301 ± 0.038 1.134 ± 0.038 1.064 ± 0.038 1.075 ± 0.038 1.062 ± 0.038 1.056 ± 0.038 1.025 ± 0.038 * Meter 1514 ** Meter--Unknown *** Meter 1472 46 ------- Table 19. RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH AIR CONDITIONING ON FOR DYNAMOMETER MEASUREMENTS OF VEHICLES WITH RADIAL TIRES BAG1 BAG2 BAGS FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 ASPEN* 1.069 ± 0.027 1.119 ± 0.017 1.093 ± 0.025 1.100 ± 0.012 1.106 ± 0.015 1.084 ± 0.014 — — — — 1.202 ± 0.027 1.160 ± 0.027 1.118 ± 0.027 1.066 ± 0.027 1.070 ± 0.027 1.119 ± 0.027 IMPALA* 1.102 ± 0.027 1.109 ± 0.016 1.089 ± 0.023 1.103 ± 0.012 1.099 ± 0.014 1.111 ± 0.017 --„ — — — — — — — — * Meter—Unknown 47 ------- Table 20. RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH AIR CONDITIONING ON FOR DYNAMOMETER MEASUREMENTS OF VEHICLES WITH BIAS TIRES BAG1 BAG2 BAGS FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 PACER* 1.099 ± 0.027 1.135 ± 0.019 1.117 ± 0.027 1.121 + 0.013 1.126 ± 0.016 1.120 ± 0.022 — — __- — 1.141 ± 0.027 1.134 ± 0.027 1.106 ± 0.027 1.041 ± 0.027 1.048 ± 0.027 1.019 ± 0.027 ASPEN* 1.081 ± 0.033 1.023 ± 0.022 1.005 ± 0.031 1.032 ± 0.016 1.015 ± 0.019 1.114 ± 0.019 — — — ___ — — — — — * Meter—Unknown 48 ------- Table 21. COMPARISON OF RATIOS OF AIR CONDITIONING/ON TO AIR CONDITIONING/OFF MPG FOR TRACK, DYNAMOMETER AND TIRE TYPE FOR SELECTED DRIVING CYCLES FTP HH HST 30 40 50 60 GRANADA 1.18 — 1.16 -- 1.19 -- 1.17 -- 1.11 — 1.12 -- 1.13 -- -- -- 1.13 -- 1.13 -- 1.10 -- 1.16 -- 1.09 -- 1.12 -- KEY; Track Dyno Radic CHEVETTE 1.10 — -- -- 1.11 -- -- -- 1.05 — -- -- 1.12 — -- -- 1.08 -- -- -- 1.03 -- -- -- 1.00 — -- -- n Bias PACER ASPEN IMPALA 1.06 -- — 1.12 1.10 -- -- 1.11 1.05 -- -- 1.04 1.06 -- -- 1.05 1.04 -- -- 1.02 1.15 -- 1.06 -- 1.11 -- 1.08 -- 1.07 -- 1.06 -- 1.10 -- 1.06 -- 49 ------- Table 22. RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH AIR CONDITIONING ON (Weighted Mean of Dynamometer, Track, Radial and Bias Tire Results) en o BAG1 BAG2 BAGS FTP HH HST CST HNO HRE HSM 10 20 30 40 50 60 70 80 GRANADA 1.127 ± 0.027 1.184 ± 0.011 1.168 ± 0.017 1.167 ± 0.010 1.177 ± 0.010 1.114 ± 0.013 — — — — 1.164 ± 0.033 1.187 ± 0.033 1.131 ± 0.033 1.133 ± 0.023 1.130 ± 0.023 1.105 ± 0.023 1.126 ± 0.023 1.017 ± 0.023 CHEVETTE 1.081 ± 0.038 1.098 ± 0.022 1.129 ± 0.030 1.101 ± 0.016 1.113 ± 0.013 1.050 ± 0.022 — — — — — 1.139 ± 0.027 1.119 ± 0.027 1.081 ± 0.027 1.033 ± 0.033 0.995 ± 0.027 1.029 ± 0.027 — PACER 1.085 ± 0.023 1.101 ± 0.012 1.121 ± 0.020 1.097 ± 0.011 1.114 ± 0.011 1.124 ± 0.016 — 1.070 ± 0.027 1.049 ± 0.027 1.086 + 0.033 1.141 ± 0.027 1.157 ± 0.019 1.101 ± 0.019 1.046 ± 0.019 1.053 ± 0.019 1.031 ± 0.019 1.001 ± 0.027 1.055 ± 0.027 ASPEN 1.075 ± 0.018 1.093 ± 0.010 1.053 ± 0.015 1.077 ± 0.008 1.073 ± 0.009 1.089 ± 0.009 — — — — 1.136 ± 0.016 1.154 ± 0.016 1.115 ± 0.016 1.056 ± 0.016 1.065 ± 0.016 1.065 ± 0.016 — — IMPALA 1.067 ± 0.018 1.099 ± 0.010 1.083 ± 0.016 1.088 ± 0.008 1.092 ± 0.010 1.083 ± 0.013 — — — — 1.199 ± 0.038 1.238 ± 0.022 1.147 ± 0.022 1.095 ± 0.022 1.071 ± 0.022 1.087 ± 0.022 1.087 ± 0.022 1.046 ± 0.022 ------- 8.8 Air Conditioning Simulation Effect Air conditioners are not normally operated during vehicle testing on dynamometers. To simulate the effect of air conditioning on fuel economy as measured on a dynamometer, the dynamometer road load at 50 mph is instead increased 10%. The ratios of fuel economy measured with air conditioning off (i.e., proper road load) to fuel economy measured with simulated air conditioning (i.e., road load increased 10%) are presented in Table 23 for both radial and bias tires. More appropriately, this analysis may be considered to be the effect on fuel economy due to a 10% increase in dynamometer power absorption unit setting. A two-way analysis of variance of the ratios among vehicles ano driving sequences yields a mean ratio of 1.0087. Thus, a 10% increase in road load produces on average less than a 1% decrease in fuel economy. This may be compared to an approximately 10% decrease in fuel economy in Table 22. The analysis of variance indicated no significant vehicle-to-vehicle ratio difference. However, a marginally significant test cycle effect was noted; however, this effect does not appear to be correlated with average test speed. 51 ------- Table 23 RATIO ± 1 STANDARD ERROR OF FUEL ECONOMY MEASURED WITH AIR CONDITIONING OFF TO FUEL ECONOMY MEASURED WITH SIMULATED AIR CONDITIONING FOR DYNAMOMETER MEASUREMENTS BAG1 BAG2 BAGS FTP HH HST' CST HNO HRE HSM 10 20 30 40 50 60 DATSUN* 0.996 ± 0.027 1.030 ± 0.017 0.996 ± 0.025 1.014 ± 0.012 1.013 ± 0.015 0.947 ± 0.017 PACER* 0.963 ± 0.033 0.983 ± 0.023 1.018 ± 0.033 0.998 ± 0.016 0.996 ± 0.020 1.016 ± 0.017 0.950 ± 0.027 0.986 ± 0.027 0.954 ± 0.027 0.992 ± 0.027 1.024 ± 0.027 0.993 ± 0.027 ASPEN** 1.020 ± 0.027 1.030 ± 0.017 1.018 ± 0.025 1.025 ± 0.012 1.024 ± 0.015 0.998 ± 1.250 1.208 ± 0.027 1.000 ± 0.027 1.021 ± 0.027 1.027 ± 0.027 1.051 ± 0.027 1.052 ± 0.027 IMPALA** I 0.971 ± 0.027 1.023 ± 0.016 \ 1.021 ± 0.023 i 1.010 ± 0.012 1.022 ± 0.014 1.044 ± 0.017 * Bias Tires ** Radial Tires 52 ------- 8.9 Effects of Modified Cycles Tables 24 and 25 present the computed ratios of the fuel economy for each modified highway test to the fuel economy of the standard highway test for dynamometer and track tests, respectively. Note from the tables that the cold start highway dynamometer and track tests represent a degradation in fuel economy of about 10% compared to the standard test. The noisy and redistributed cycle tests impose a 3%-5% fuel economy penalty on both the dynamometer and the track. The smooth and 50 mph cruise cycles result in a 4% to 8% fuel economy improvement over the standard cycle. In some instances, vehicle to vehicle differences among the ratios can be statistically inferred both from the dynamometer and track tests. Even so, we present the mean ratios over all vehicles for each modified test and note that the mean ratios from dynamometer tests are statistically undistinguishable from the mean ratios from the track tests. A comparison of the modified test cycles with the standard highway cycle is presented in Appendix A. 53 ------- Table 24. RATIO OF MODIFIED HIGHWAY TEST MPG TO STANDARD HIGHWAY TEST MPG FOR DYNAMOMETER TESTS (Air Conditioner Off) Datsun Pinto Honda Chevette Pacer Aspen Impala Mean Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias COLD START (CST) 0.885 ± 0.021 0.890 ± 0.017 — 0.892 ± 0.019 0.893 ± 0.017 — — 0.920 ± 0.021 0.940 ± 0.023 0.933 ± 0.022 0.908 ± 0.008 NOISY CYCLE 1.015 ± 0.014 0.981 ± 0.017 0.962 ± 0.016 1.000 ± 0.017 — 0.952 ± 0.015 0.933 ± 0.014 0.966 ± 0.017 0.969 ± 0.015 0.972 ± 0.005 REDISTRIBUTED CYCLE 1.000 ± 0.014 0.873 ± 0.017 0.964 ± 0.016 1.003 ± 0.017 — 0.930 ± 0.016 0.926 ± 0.013 0.947 ± 0.019 0.988 ± 0.015 0.954 ± 0.006 SMOOTH CYCLE 1.072 ± 0.014 1.034 ± 0.016 1.028 ± 0.016 — 1.046 ± 0.016 1.036 ± 0.014 1.062 ± 0.017 1.034 ± 0.015 1.045 ± 0.006 50 MPH CRUISE 1.083 ± 0.016 1.055 ± 0.017 1.067 ± 0.017 1.067 ± 0.022 1.066 ± 0.019 — 1.063 ± 0.022 1.103 ± 0.021 1.143 ± 0.023 1.091 ± 0.022 1.082 ± 0.007 ------- Table 25. RATIO OF MODIFIED HIGHWAY TEST MPG TO STANDARD HIGHWAY TEST MPG FOR TRACK TESTS (Air Conditioner Off) Datsun Pinto Honda Chevette Pacer Aspen Impala Mean Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias Radial Bias COLD START (CST) — 0.876 ± 0.027 0.906 ± 0.029 0.804 ± 0.029 0.934 ± 0.038 0.931 ± 0.030 0.937 ± 0.031 0.898 ± 0.012 NOISY CYCLE 0.963 ± 0.017 0.981 ± 0.025 0.965 ± 0.022 0.984 ± 0.025 0.939 ± 0.022 0.965 ± 0.033 0.988 ± 0.033 0.945 ± 0.020 0.985 ± 0.022 0.968 ± 0.008 REDISTRIBUTED CYCLE 0.935 ± 0.019 0.975 ± 0.025 0.960 ± 0.022 0.963 ± 0.025 0.961 ± 0.022 0.964 ± 0.033 0.977 ± 0.033 0.972 ± 0.019 0.995 ± 0.022 0.967 ± 0.008 SMOOTH CYCLE 1.047 ± 0.019 1.100 ± 0.027 1.061 ± 0.029 1.042 ± 0.025 1.051 ± 0.022 1.061 ± 0.033 1.121 ± 0.038 1.049 ± 0.019 1.071 ± 0.022 1.067 ± 0.008 50 MPH CRUISE 1.093 ± 0.022 — 0.952 ± 0.022 0.906 ± 0.025 1.081 ± 0.029 1.091 ± 0.033 1.211 ± 0.033 1.157 ± 0.030 1.126 ± 0.025 1.077 ± 0.010 ------- 8.10 Computed Road Load Horsepower From Coast Downs Coast-down tests were conducted on the track and dynamometer on vehicles equipped with bias belted and radial tires. The quantities that were measured were vehicle direction (i.e., north, south, curve for track tests), wind speed, wind direction, and time in seconds for the vehicle to coast from 55 mph to 45 mph. Coast-down tests were also conducted on the track to measure the effect of the vehicles' windows being up or down and on the dynamometer to measure the effect of air conditioning off or simulated. The coast-down results are presented in Table 26. Table 26 also presents the calculated Road Load Horsepower (RLHP) at 50 mph. This quantity is calculated from the coast-down times by the expression RLHP = i^tia weight (Ibs) (0>06073)* coast-down time (sees) For the track tests, the effect of track grade is eliminated by averaging the coast-down times for two different track directions (e.g., north and south). The RLHP calculated is the total horsepower required to overcome both rolling and aerodynamic resistance for a vehicle with a particular inertia weight as tested on the track or dynamometer. One way of assessing the dynamometer-to-track effect due to improper RLHP simulation on the dynamometer is to ratio the RLHP determined from track tests to the RLHP determined from dynamometer tests. These ratios are presented in Table 27 for radial and bias tires for tests with air conditioning off and windows up. Note that the ratio for bias tires is consistently larger than the corresponding ratio for radial tires for each of the vehicles tested. This is consistent with the notion that the rolling resistance of radial tires is less than the rolling resistance of bias tires. Also note that in all but two instances, the ratios (bias and radial) are less than unity and this would seem to imply that the track road load horsepower necessary to overcome rolling and aerodynamic resistance is less than the dynamometer road load horsepower. * See Appendix F for derivation of formula, 56 ------- Table 26(a) MEASURED COAST-DOWN TIMES AND CALCULATED ROAD LOAD HORSEPOWER FOR DYNAMOMETER AND TRACK TESTS VEHICLE PINTO IMPALA ASPEN SITE TRACK DYNO #5 TRACK DYNO #5 TRACK DYNO #5 TEST WEIGHT (Ibs) 3150 3000 4869 5000 4318 4000 DIRECTION N S N S N S W. Curve E. Curve N/A N S N/A N S N S N/A TIRE TYPE R B R B R R B R B R B WIND SPEED (mph) 1 6 N/A 3 N/A 6 1 N/A WIND** DIRECTION (deg) 90 335 N/A 272 N/A 328 323 N/A WINDOWS UP DOWN UP N/A UP N/A UP N/A A/C* OFF OFF OFF OFF SIM. OFF SIM. OFF OFF SIM. OFF SIM. AVG. TIME FROM 55 TO 45 MPH (sees) 13.07 15.23 12.80 14.13 11.83 14.27 12.30 13.10 12.40 13.80 15.00 20.20 14.14 14.00 14.60 13.93 13.86 19.66 14.00 17.46 12.34 14.00 12.93 12.23 CALCULATED RLHP (3 50 MPH 13.52 14.21 14.66 15.06 14.69 13.20 16.80 21.47 21.69 20.80 21.80 15.65 16.67 19.6.9 20.47 18.79 19.86 * A/C = Airconditioning ** Relative to North. ------- Table 26(b) MEASURED COAST-DOWN TIMES AND CALCULATED ROAD LOAD HORSEPOWER FOR DYNAMOMETER AND TRACK TESTS en OO VEHICLE GRANADA PACER DATSUN SITE TRACK DYNO #5 TRACK DYNO #5 TRACK DYNO #5 TEST WEIGHT (Ibs) 3978 4000 3776 3500 2497 2250 DIRECTION N S N S E. Curve W. Curve N/A N S N S N S N/A N S N S N S N S N/A TIRE TYPE R B R B R B R B B R R B WIND SPEED (mph) 5 4.5 N/A 0 4 N/A 6.5 4.5 6.0 7.0 N/A WIND** DIRECTION (deg) 157 20 N/A 0 90 N/A 300 270 300 270 N/A WINDOWS UP N/A DOWN UP UP N/A UP DOWN UP DOWN N/A A/C* OFF OFF OFF OFF SIM. flFF Urr OFF AVG. TIME FROM 55 TO 45 MPH (sees) 14.90 14.00 11,45 11.60 11.60 12.40 13.60 13.87 14.03 14.83 16.03 17.33 15.30 17.27 13.00 13.50 12.80 12.00 12.60 11.53 12.20 13.90 13.00 13.00 11.80 10.77 10.99 CALCULATED RLHP (3 50 MPH 16.72 18.66 20.13 17.86 17.51 15.89 13.75 14.08 16.35 15.74 16.61 12.33 12.78 11.27 12.23 12.69 12.43 * A/C = Air Conditioning ** Relative to North ------- Table 27 RATIO OF RLHP DETERMINED FROM TRACK COAST-DOWN TESTS TO RLHP DETERMINED FROM DYNAMOMETER COAST-DOWN TESTS (AIR CONDITIONING OFF/WINDOWS UP) VEHICLE PINTO IMPALA ASPEN GRANADA PACER DATSUN TIRE TYPE BIAS 1.111 — 0.887 1.066 0.895 0.992 RADIAL 0.920 0.782 0.795 0.936 0.841 0.888 RATIO OF TRACK TEST WEIGHT TO DYNO TEST WEIGHT 1.05 0.97 1.08 0.99 1.08 1.11 59 ------- 9.0 DISCUSSION This test program and analysis attempts to identify, quantify, and statistically verify the individual parameters contributing to dynamometer to track fuel economy differences. To this end, the testing of each vehicle is carefully controlled both for dynamometer and for track tests to every extent possible. Each vehicle was inspected and tuned to manufacturers' specifi- cations before testing began, so that any fuel economy differences due to vehicle state-of-tune could be eliminated. Also, to the extent possible, each vehicle was tested on the track at ambient temperatures within the same range (68°F to 86°F)* as that required by the FTP for dynamometer tests. Effects of wind and grade, which are not simulated on dynamometer tests, were compensated for on track tests by conducting the test cycle in two opposing directions and averaging the resulting measurements. Odometer mileage also can affect fuel economy and can contribute to dynamometer to track variability. The odometer readings for the vehicles tested ranged from approximately 2000 to 11000 miles. In most cases, however, there were only a few hundred miles difference between the points at which the vehicles were tested from dynamometer to track. The above differences in testing conditions from dynamometer to track were considered to be small. That is, differences in temperature and mileage (uncontrolled parameters considered to possibly influence fuel economy) were judged to be small contributors to fuel economy variability compared to measurement variability. Thus, no attempts were made to correct fuel economy for vehicle mileage or ambient temperature. Fuel economy measured on the dynamometer is normally calculated by the carbon balance method. In this study, it was determined that the differences between meter fuel consumption and carbon balance fuel consumption were a function of the particular meter used as well as the magnitude of fuel consumption. Therefore, comparisons between fuel economy on the track and dyno were always made using the same or equivalently adjusted meter (i.e., for purposes of presentation meter #1514 was arbitrarily chosen and fuel consumptions measured with different meters were corrected by whatever the offset was determined to be between it and meter 1514). In a few instances, tests were conducted at ambient temperatures as low as 50°F, but never above 86 F. 60 ------- Dynamometer measured fuel economy divided by track measured fuel economy provides a measure of the dyno/track effect. As determined in the analysis, no statistically significant differences between the ratios computed for air conditioning on and air conditioning off are detectable. However, vehicle to vehicle differences between ratios do exist. Further, there is a difference between ratios due to tire type (i.e., radial and bias belted). If we compare the FTP ratios presented in Table 28 it may be noted that fuel economy as measured on the dynamometer is greater than the fuel economy measured on the track for all cases. Except for the Honda, the ratio is larger for the vehicle tested with bias tires as compared to the same vehicle tested with radial tires. We note two factors that may be responsible for the reverse effect in the Honda. First, the Honda is the only front-wheel drive vehicle in the group, and second, the Honda was tested with 12" bias tires and 13" radial tires. Table 28. COMPARISON OF DYNAMOMETER TO TRACK FUEL ECONOMY RATIOS AS MEASURED OVER THE FTP (Mean Ratio ±1 Standard Error) TIRE TYPE Radial Bias PINTO 1.05U0.014 1.106±0.015 HONDA 1.114±0.011 1.097±0.013 PACER — 1.057±0.013 ASPEN 1.086±0.010 1.140±0.014 Table 29 presents the ratios of fuel economy as measured with radial tires to the fuel economy as measured with bias tires for both dyna- mometer and track FTP tests. Note in the table, that the ratios computed for dynamometer tests are all less than unity except for the Honda. This seems to imply that fuel economy of a vehicle measured on a dynamometer is less if it is equipped with radial tires as compared to bias belted tires. Another way of saying the same thing is that the rolling resistance of radial tires is greater than the rolling resistance of bias tires when tested on the dynamometer. 61 ------- Table 29 COMPARISON OF THE RATIOS OF FUEL ECONOMY MEASURED WITH RADIAL TIRES TO FUEL ECONOMY MEASURED WITH BIAS TIRES FOR DYNAMOMETER AND TRACK (Mean Ratios ±1 Standard Error) VEHICLE Pinto Honda Datsun Chevette Pacer Aspen Impala Granada DYNAMOMETER 0.967 ± 0.012 1.022 ± 0.010 0.984 ± 0.010 — — 0.992 ± 0.009 0.996 ± 0.012 — TRACK 1.018 ± 0.017 1.006 ± 0.014 1.005 ± 0.014 1.030 ± 0.016 — 1.057 ± 0.015 1.080 ± 0.010 0.970 ± 0.013 For track tests, it may be noted from Table 29 that the ratios are greater than unity (except for the Granada). This implies that for track tests fuel economies for vehicles equipped with radial tires are greater than fuel economies for vehicles equipped with bias tires (i.e., rolling resistance is greater for bias tires than for radial tires on track tests). Another way to assess and compare the ratios in Tables 28 and 29, is to compute the ratios of the ratios. For example, Table 28 compares the ratios of dynamometer fuel economy to track fuel economy.for vehicles with radial tires (DR/TR) and for vehicles with bias tires (DB/Tg>. The ratio of these two ratios may be written: VTR VTB V°B VTB Note that (DR/DB)/(TR/TB) is exactly the ratio of the ratios presented in Table 29. On the other hand, it is observed in Table 30 that the two alternatively calculated ratios of the ratios are not exactly equal. This is explained by the fact that in some cases a different number of tests were available for the dynamometer to track comparisons than were available for radial to bias tire comparisons on the same vehicle. 62 ------- Table 30. COMPARISON OF THE RATIO OF RATIOS BY TWO METHODS Pinto Honda Datsun Aspen Impala VDB VTB 0.950 ± 0.021 1.016 ± 0.017 0.979 ± 0.019 0.939 ± 0.017 0.922 ± 0.016 °R/TR °B/TB 0.950 ± 0.021 1.015 ± 0.019 — 0.953 ± 0.017 — Because the same meter was not always used to measure both dynamometer and track fuel consumptions, fewer comparisons could be made, in general, between the fuel economies from dynamometer to track than between fuel economies from radial to bias tires. If the relative tire/track interactions of radial and bias tires were properly simulated by the dynamometer, then the dynamometer-to-track MPG ratio for radial tires would equal the dynamometer-to-track MPG ratio for bias tires (i.e., the ratio of the ratios would be unity). From Table 30 note that this is not true. In most cases, the ratio of the ratios is less than unity, and the magnitude of deviations is as much as 8%. The implication is that the relatively higher fuel economy achieved on the average with radial tires on the track is not reproduced on the dynamometer. A previous study of tire-surface interaction by Burgeson6 sheds some light on reasons for the discrepancy between dynamometer and track results. Burgeson's study investigated the rolling resistive forces on 29 pairs of tires ranging in size from BR78xl3 to LR78xl5 and consisting of radial, bias belted, and bias ply construction. The pairs of tires were tested on a small twin-roll dynamometer (r ~ 5") and on a large single-roll dynamometer (r -24"). No aerodynamic losses were simulated (i.e., no PUA settings). The power absorbed by the dynamometers due to only rolling resistive losses were calculated from coast-down times on both the large and small roll dynamometers. 63 ------- It is generally assumed in the dynamometer test procedure that the power absorbed by a tire (inflated to 45 psi) on the dynamometer is twice that of the tire (inflated to a typical 26 psi) on the road. That is, one might expect a rolling resistive force, FR, measured on the dual small roll dynamometer (at 45 psi) to be twice that force measured on a flat surface (at 26 psi). The rolling resistance determined from measurements with two tires at 45 psi on a small-roll Clayton Dynamometer was compared to the rolling resistance determined from corrected results on the large roll dynamometer. The results are reproduced in Table 31 and show that the ratio R£ of the mean rolling force on the small roll dynamometer at 45 psi to the corrected mean rolling force on a flat surface for different tire types is less than the expected factor of two and varies by tire type. From the table, note that radial tires come closest to producing a ratio of 2. In general, it may be inferred from Burgeson's results that the Clayton twin-roll dynamometer underloads vehicles (i.e., the force due to rolling resistance measured on the dynamometer is less than that actually measured on the road). Furthermore, this dynamometer underloading effect is more severe for bias belted tires than for radial, which is in qualitative agreement with Table 30. Table 31. RATIO (RC) OF THE MEAN HORSEPOWER (PR) DUE TO ROLLING RESISTANCE MEASURED ON A SMALL TWIN-ROLL DYNAMOMETER TO THE MEAN HORSEPOWER DUE TO ROLLING RESISTANCE MEASURED ON A LARGE ROLL DYNAMOMETER AND CORRECTED TO ROAD* Tire Type Radial Bias Belted Bias Clayton (Tires at 45 psi) P Clayton (hp) K 7.67 6.99 7.81 Large Roll Corrected to Road (Tires at 26 psi) PD Road (hp) K 4.15 5.04 5.25 ,PD Clayton n - K . 1XC PD Road K 1.85 1.39 1.49 * Extracted from Reference 6. 64 ------- The results in Table 31 should be viewed qualitatively inasmuch as the magnitude of the ratio, RC, obtained by Burgeson may not be correct for all tire/vehicle combinations. The reason for this is discussed by Burgeson. Radial and bias tires exhibit ranges of rolling resistance characteristics that may vary by tire manufacturer and vehicle configuration, There may be high and low rolling resistance radial and bias tires and tire-track surface interactions may be different from tire-dynamometer surface interactions. Consistent with the above, the dynamometer to track MPG ratios computed in this study are seen to vary significantly from vehicle to vehicle. The vehicle-to-vehicle effect is more appropriately defined as a vehicle/tire configuration effect. In addition to the contributions that rolling resistance variations make to fuel economy differences are the contributions of aerodynamic resistance. Newell7 has investigated the extent to which manufacturer supplied PAU settings (i.e., aerodynamic resistive force) agreed with aerodynamic forces measured on ten production vehicles. In this program, vehicles were chosen for test if their manufacturer supplied PAU settings were atypically low compared to PAU settings for other similar vehicles. Vehicle road load horsepowers (aerodynamic and rolling resistance contributions) were determined from coast-down tests on a test track. The RLHPs were corrected to an ambient air temperature of 68°F and barometric pressure of 29.00 inches Hg. The vehicle was then set up on a twin small-roll dynamometer and the PAU was set to a value that reproduced the same coast-down time that was measured on the test track. The PAU values obtained in this way were compared with the PAU values submitted by the manufacturer for that vehicle. The manufacturer and test determined PAU settings in horsepower are reproduced in Table 32. From Table 32, note that the manufacturers' recommended PAU settings are consistently lower than those measured from the production vehicles (except for the Omni, a front-wheel drive vehicle). Also presented in Table 32 are the total RLHP calculated from coast-down times in Newell's tests. The difference between total RLHP and PA (the PAU setting) is the implied power dissipated due to rolling resistance. The calculated values range from 4.0 to 8.0 HP and do not compare with the power dissi- pation results due to rolling resistance computed by Burgeson in Table 31 and which range from 8.3 to 10.5 HP. 65 ------- Table 32 COMPARISON OF DYNAMOMETER POWER ABSORBER (PA) SETTINGS IN HP* 01 CTl '79 VEHICLE Fiesta Omni Monza Granada Firebird Lebaron Corvette Eldorado Trans Am Olds '98 PA MFR. (PAU) 7.3 7.8 8.1 10.1 8.8 10.8 8.0 9.6 9.5 11.6 PA STUDY (PAU) 8.05 7.8 11.3 12.6 10.0 11.6 9.4 10.0 9.9 12.2 PT TOTAL RLHP (MFR) 12.2 12.7 -- 13.7 1 14.9 16.3 _- | 16.4 15.3 18.1 j PT TOTAL RLHP (STUDY) 12.0 11.8 15.9 17.8 14.3 16.9 17.4 17.4 14.4 18.2 PR IMPLIED ROLLING RESISTANCE (TOTAL RLHP- PAU) STUDY 3.95 4.0 4.6 5.2 4.3 5.3 8.0 7.4 4.5 6.0 * Extracted, in part, from Reference 7. ------- There are several possible reasons for the apparent discrepancy in power dissipation measurements and calculations due to rolling resistance. The first and most obvious reason for the differences in rolling resistance has previously been discussed and refers to the wide range of rolling resistance characteristics possible for both radial and bias tires. Second, Burgeson's estimates of track rolling resistance were made by testing tires on a large roll dynamometer (r -24") at 45 psi. He had to correct his results to account for roll curvature and tire pressure. Klingbeil8 has shown that the curvature correction formula most often used (due to Clark9 and used by Burgeson) does not correctly account for curvature due to thermal effects. If this is the case, Burgeson's absolute estimates of track rolling resistance are too high. Third, Newell's estimates of the contribution of aerodynamic resistive forces seem to be too large a fraction of total road load horsepower (e.g., 54% to 71%). Newell's estimates of aerodynamic forces are higher than the manufacturers' estimates even though his estimates of total road load horsepower at 50 mph are consistent with manufacturer supplied total road load horsepower. Newell cites tire-surface interaction effects and possible dynamometer calibration differences as possible reasons for the observed differences between his test-determined PAU settings and those submitted by the manufacturer. Results of coast down tests on six of the eight vehicles in this test program indicate that total road load horsepower at 50 mph (RLHP) is, in general, lower on track tests than on dynamometer tests. This is exactly opposite what would be expected on the basis of fuel economy comparisons. Nevertheless, the relative relationship of the imputed rolling resistance of radial-to-bias tires on the track as compared to that on the dynamometer is consistent with the fuel economy ratio of ratios presented in Table 30. However, since we cannot accurately resolve the contributions of rolling and aerodynamic forces for these vehicles tested, we cannot completely account for the RLHP differences from track- to-dynamometer tests. Recent studies by Yurko10 and Gugett11 have shown another possible influence on vehicle fuel economy as measured on a dynamometer. Yurko and Grugett have shown that there is a velocity difference (i.e., a slip) between the front and rear rolls of a small twin-roll dynamometer due to tire deformation. The effective tire radius on the rear roll is greater than the effective tire radius on the front roll. Therefore the rotational velocity of the front roll is less relative to the rear roll. 67 ------- As is presently the case for a small twin-roll dynamometer, the major tractive load imposed on the vehicle is applied at the front roll. The rear roll is presently uncoupled from the front roll and is used to determine speed. Since the fuel economy, as calculated over a specified driving sequence, is dependent on the speed of (and distance traveled by) the rear roll, fuel economy estimates are greater than they would be if speed was measured from the front roll. Results of testing by Yurko with one 1978 Mercury Montego indicate that the velocity differences between the rolls were least when the rolls we*-e coupled (e.g., a -0.22%*'velocity difference for radial tires and a 0.40% velocity difference for bias tires). Coast-down tests with radial tires indicated that the coupling of the rolls resulted in a 2% to 6% increase in measured fuel consumption rate as compared to the case when the rolls were uncoupled. Grugett measured the fuel consumption differences due to the coupling of the dynamometer rolls as compared to the uncoupled case over the urban and highway driving cycles. Tests were conducted with one 1979 Chevrolet Nova on a test track, on a small twin-roll dynamometer with rolls uncoupled, and on a small twin-roll dynamometer with the rolls coupled. Tests showed that the uncoupled dynamometer tests overestimated fuel economy by about 10% over track tests. Coupled dynamometer tests overestimated fuel economy by about 4%. Additional studies are needed to verify the vehicle tire slip influence on fuel economy as measured on a dynamometer. Preliminary investigations indicate that coupling of the front and rear rolls of the dynamometer might account for as much as 6% of the approximate 10% difference in fuel economy measured between dynamometer and track. Tests need to be conducted on a test track, and on a coupled and uncoupled dynamometer using different size and technology vehicles (i.e., front and rear wheel drive), and different tire types. Additional investigations within the present study indicate that the use of air conditioning results in an increase in fuel consumption of from 7% to 18% measured over the FTP urban cycle. The increase in fuel consumotion due to the use of air conditioning is independent of track or dynamometer testing and of tire type. However, the increase in fuel consumption does vary significantly from vehicle to vehicle. The rotational velocity of the front roll was 0.22% larger than the rear roll. 68 ------- At present, the impact on fuel economy due to air conditioning is simulated on the dynamometer by increasing the dynamometer road load (PAD) at 50 mph by 10%. This study found that the dynamometer simulation of air conditioning did not produce any significant change in measured fuel economy. Dynamometer simulated air conditioning is not a good indication of the effect on fuel economy due to the use of air conditioning in actual practice. Finally, effort was expended in this study to determine the extent to which different types of driving, similar to highway driving, affected vehicle fuel economy. Public criticism over the EPA estimated highway fuel economy of vehicles has raised doubts as to whether the highway estimate is attainable. Tests in the study over modified highway cycles demonstrate highway fuel economies that are as much as 10% lower or 8% higher than the fuel economies estimated over the standard EPA highway cycle. The tests demonstrated that highway type driving characterized by smooth steady driving resulted in a highway fuel economy approximately 6% larger than the EPA estimate. Driving at a constant 50 mph resulted in an 8% increase in fuel economy over the EPA highway cycle fuel economy. On the other hand, highway type driving characterized by a greater percentage of time either accelerating/decelerating or at speeds above 60 mph resulted in significant decreases in fuel economy of about 3-4% compared to EPA estimates. Cold start highway fuel economy was about 9%-10% lower than EPA highway cycle fuel economy. In all cases, the dynamometer produced statistically equivalent effects on fuel economy due to the modified cycles as those produced on track tests. 69 ------- REFERENCES 1 Technology Assessment and Evaluation Branch, ECTD, OMSAPC, EPA, "Passenger Car Fuel Economy—Dynamometer vs. Track vs. Road," Report 76-1, August 1975. 2 D. Turton, "Fuel Consumption Measurements—Carbon Balance vs. Flow Meter," EPA Technical Report, SDSB79-28, July 1979. 3 T. Newell, "Carbon Balance and Volumetric Measurements of Fuel Consumption," EPA Technical Report, SDSB80-05, April 1980. 4 S. Kaufman, "Individual Manufacturer Procedures to Establish Fuel Economy Adjustment Factors," Falcon Research and Development Company, Report No. 3520-4/BUF-42, Appendix A, February 1981. 5 F. P. Hutchins and J. Kranig, "An Evaluation of the Fuel Economy Performance of Thirty-one 1977 Production Vehicles Relative to Their Certification Counterparts," EPA Report 77-18FPH (TAEB), January 1978. 6 Richard N. Burgeson, "Tire-Dynamometer Roll Effects," EPA Technical Report LDTP-77-4, March 1978; Richard N. Burgeson, "Clayton Dynamometer-to-Road Tire Rolling Resistance Relationship," EPA Technical Report LDTP-78-09, April 1978. 7 Terry Newell, "Independent Coast-Down Road Load Power Determination for Ten Diverse Production Vehicles," EPA Technical Report SDSB-80-15, August 1980. 8 W. W. Klingbeil, "Theoretical Prediction of Test Variable Effects, Including Twin Rolls, on Rolling Resistance," SAE Paper 800088, February 1980. 9 S. K. Clark, "Rolling Resistance Forces in Pneumatic Tires," Dept. of Transportation, UM-013658-1-1, DOT-TSC-76-1, January 1976. 10 John Yurko, "Computer Simulation of Tire Slip on a Clayton Twin Roll Dynamometer," EPA Technical Report SDSB-79-10, February 1979; John Yurko, "A Track to Twin Roll Dynamometer Comparison of Several Different Methods of Vehicle Velocity Simulation," EPA Technical Report SDSB-79-26, June 1979. 11 Bruce Grugett, "Vehicle Fuel Economy Track vs. Dynamometer," EPA Technical Report SDSB-80-8, June 1980. 70 ------- APPENDIX A COMPARISON OF MODIFIED AND STANDARD HIGHWAY CYCLES 71 ------- APPENDIX A Table A-l COMPARISON OF MODIFIED AND STANDARD HIGHWAY CYCLES Distance, Miles Time, Seconds Average Speed, mph Minimum mph* Maximum mph Stops per Mile STANDARD CYCLE 10.24 765 48.2 28.4 59.5 0.098 SMOOTH CYCLE 10.23 765 48.1 50.0 50.0 0.098 NOISY CYCLE 10.26 765 48.3 25.1 63.0 0.097 REDISTRIBUTED CYCLE 10.56 765 49.7 18.1 72.5 0.095 PERCENT TIME IN SPEED RANGES Idle 0-10 mph 10-20 mph 20-30 mph 30-40 mph 40-50 mph 50-60 mph 60-70 mph > 70 mph 0.5 2 1 2 8 41 46 0 0 0.5 2 1 1 1 3 92 0 0 0.5 2 1 2 9 38 46 2 0 0.5 2 1 3 10 25 40 16 2 * Excluding initial acceleration and final deceleration. 72 ------- Table A-2 DISTRIBUTION OF TIME SPENT IN ACCELERATION AND SPEED RANGES: Standard EPA Highway Cycle ACCELERATION RATE (MPH/sec) Total % of Time in Speed Range 0-10 10-20 SPEED (MPH) 20-30 30-40 40-50 1.8 1.1 2.0 7.7 40.8 50-60 3.6 3.0 2.4 1.8 1.2 0.6 0 0 -0.6 -1.2 -1.8 -2.4 -3.0 -3.6 -4.2 -4.8 ... 4.2 ... 3.6 ... 3.0 ... 2.4 ... 1.8 ... 1.2 ... 0.6 Zero ... -0.6 ... -1.2 ... -1.8 ... -2.4 ... -3.0 ... -3.6 ... -4.2 ... -4.8 ... -5.4 2 3 1 2 1 1 3 1 4 1 1 1 2 3 1 3 1 2 1 2 1 1 4 1 15 19 6 7 3 3 7 73 103 100 21 4 3 1 1 57 141 151 6 1 46.7 73 ------- Table A-3 DISTRIBUTION OF TIME SPENT IN ACCELERATION AND SPEED RANGES: Smooth Highway Cycle ACCELERATION RATE (KPH/sec) 0-10 10-20 SPEED (HPH) 20-30 30-40 40-50 50-60 3.6 3.0 2.4 1.8 1.2 0.6 0 0 -0.6 -1.2 -1.8 -2.4 -3.0 -3.6 -4.2 -4.8 ... 4.2 ... 3.6 ... 3.0 231 ... 2.4 2 ... 1.8 1 232 ... 1.2 4 6 ... 0.6 3 1 Zero 4 702 ... -0.6 6 ... -1.2 1 3 ... -1.8 3 2 ... -2.4 1 3 1 ... -3.0 2 1 2 ... -3.6 1 3 ... -4.2 ... -4.8 ... -5.4 Total % of Time in Speed Range 1.8 0.9 1.2 1.3 2.9 91.8 74 ------- Table A-4 DISTRIBUTION OF TIME SPENT IN ACCELERATION AND SPEED RANGES: Noisy Highway Cycle ACCELERATION RATE SPEED (MPH) (MPH/sec) 3.6 3.0 2.4 1.8 1.2 0.6 0 0 -0.6 -1.2 -1.8 -2.4 -3.0 -3.6 -4.2 -4.8 ... 4.2 ... 3.6 ... 3.0 ... 2.4 ... 1.8 ... 1.2 ... 0.6 Zero ... -0.6 ... -1.2 ... -1.8 ... -2.4 .. . -3.0 ... -3.6 ... -4.2 ... -4.8 ... -5.4 0-10 10-20 20-30 1 2 1 3 1 1 1 2 7 1 1 2 2 2 1 1 1 2 1 1 1 1 1 30-40 1 2 1 7 16 10 14 6 4 2 1 1 1 1 40-50 9 24 59 62 93 23 9 3 2 1 1 1 2 50-60 60-70 19 1 67 3 110 5 128 6 24 3 5 1 Total % of Time in Speed Range 1.8 0.9 2.1 37.8 46.3 2.3 75 ------- Table A-5 DISTRIBUTION OF TIME SPENT IN ACCELERATION AND SPEED RANGES: Redistributed Highway Cycle ACCELERATION RATE (MPH/sec) -3.6 ... -4.2 -4.2 ... -4.8 -4.8 ... -5.4 Total % of Time in Speed Range 0-10 10-20 20-30 SPEED (MPH) 30-40 40-50 50-60 60-70 70-80 3.6 3.0 2.4 1.8 1.2 0.6 0 0 -0.6 -1.2 -1.8 -2.4 -3.0 ... 4.2 ... 3.6 ... 3.0 ... 2.4 ... 1.8 ... 1.2 ... 0.6 Zero ... -0.6 ... -1.2 ... -1.8 ... -2.4 ... -3.0 ... -3.6 2 3 1 1 1 4 1 2 1 2 3 1 3 2 1 2 5 3 1 1 4 4 1 2 1 1 8 16 19 25 4 3 9 40 55 64 18 5 1 1 83 17 95 56 112 49 11 3 2 1 7 6 1 1.8 1.8 3.3 9.9 25.1 39.8 16.3 1.8 76 ------- APPENDIX B TEST VEHICLE-DESCRIPTIONS 77 ------- APPENDIX B TEST VEHICLE-DESCRIPTIONS 1. CHASSIS MODEL YEAR MAKE - 1976 Honda CVCC Civic EMISSION CONTROL SYSTEM - Honda CVCC Engine Type . 4-stroke prechamber, stratified charge, spark ignited, single OHC, in-line 4 cyl. Bore x Stroke . 2.91 x 3.41 in./74 x 86.5 mm Displacement 90.8 CID/1488 cc Compression Ratio 7.9:1 Maximum Power at rpm , 60 hp kW at 5000 rpm Fuel Metering Single carburetor with progressive 2 bbl for combustion chamber and 1 bbl for pre- chamber Fuel Requirement 91 RON Drive Train Transmission Type 4 speed manual Final Drive Ratio ... 3.875:1 Chassis Type Unitized body, front transverse mounted engine, front wheel drive Tire Size OEM Goodrich 6.005x12 and OEM Michel in 155SRxl3 Curb Weight 1795 lb/815 kg Inertia Weight ..... 2000 lb/910 kg Passenger Capacity Four 78 ------- Emission Control System Basic Type Prechamber stratified charge with thermal reactor and PCV Mileage on Vehicle 5,460 miles 79 ------- 2. CHASSIS MODEL YEAR/MAKE - 1976 Datsun B-210 EMISSION CONTROL SYSTEM - EGR, Air Injection Engine Type 4-stroke Otto Cycle, OHV, in-line, 4 cyl. Bore x Stroke 2.99 x 3.03 in./76 x 77 mm Displacement ..... 85 cu. in./1397 cc Compression Ratio 8.5:1 Maximum Power at rpm . . 80 hp/60 kW at 6000 rpm Fuel Metering .......... Single progressive 2 bbl carburetor Fuel Requirement . 91 RON low lead Drive Train Transmission Type ........ 4 speed manual Final Drive Ratio 3.89:1 Chassis Type ...... .... Unitized body, front engine, rear wheel drive Tire Size ... .... OEM Toyo 155SRxl3 and OEM Bridgestone 155x13 Curb Weight ..... 1965 lb/890 kg Inertia Weight .......... 2250 lb/1020 kg Passenger Capacity ... Four Emission Control System Basic Type EGR, PCV, air injection Mileage on Vehicle 3,600 miles 80 ------- 3. CHASSIS MODEL YEAR/MAKE - 1976 Ford Pinto EMISSION CONTROL SYSTEM - Catalyst, EGR, Air Injection Engine Type 4-stroke, Otto cycle, OHC, in-line, 4 cyl. Bore x Stroke 3.78 x 3.13 in.796.0 x 79.5 mm Displacement ........... 140 cu. in./2300 cc Compression Ratio ... 9.0:1 Maximum Power at rpm ....... 92 hp/69 kW at 5000 rpm Fuel Metering . . . Single 2 bbl carburetor Fuel Requirement 91 RON unleaded Drive Train Transmission Type . 3 speed automatic Final Drive Ratio .. 3.18:1 Chassis Type ....... Unitized body, front engine, rear wheel drive Tire Size . . OEM Goodyear A78xl3 and OEM Goodyear BR78xl3 Curb Weight 2587 lb./1175 kg Inertia Weight . 3000 Ib.71360 kg Passenger Capacity ........ Four Emission Control System Basic Type Single monolith noble metal catalyst, EGR5 PCV, air injection Mileage on Vehicle 10,220 miles 81 ------- 4. CHASSIS MODEL YEAR/MAKE - 1976 AMC Pacer EMISSION CONTROL SYSTEM - EGR Engine Type 4-Stroke Otto Cycle, OHV, in-line, 6 cyl. Bore x Stroke 3.75 x 3.50 in./95 x 89 mm Displacement 232 CID/3802 cc Compression Ratio . 8.0:1 Maximum Power at rpm ....... 90 hp/67 kW at 3050 rpm Fuel Metering .......... Single one bbl carburetor Fuel Requirement 91 RON Drive Train Transmission Type . 3 speed automatic Final Drive Ratio . 3.08:1 Chassis Type ............... Unitized body, front engine, rear wheel drive Tire Size OEM Goodyear DR70xl4 and OEM Goodyear 6.95x14 Curb Weight 3330 lb/1510 kg Inertia Weight 3500 lb/1590 kg Passenger Capacity Five Emission Control System Basic Type EGR, PCV Mileage on Vehicle . 4,940 miles 82 ------- 5. CHASSIS MODEL YEAR/MAKE - 1976 Ford Granada EMISSION CONTROL SYSTEM - Catalyst, EGR, Air Injection Engine Type .............. 4-stroke Otto cycle, OHV, in-line, 6 cyl. Bore x Stroke 3.68 x 3.91 in./93 x 99 mm Displacement .......... 250 CID/4100 cc Compression Ratio ....... 8.0:1 Maximum Power at rpm ...... 86 hp/64 kW at 3000 rpm Fuel Metering ......... Single one bbl carburetor Fuel Requirement ........ 91 RON unleaded Drive Train Transmission Type ....... 3 speed automatic Final Drive Ratio . 3.07:1 Chassis Type .............. Unitized body, front engine, rear wheel drive Tire Size ........... OEM Goodyear DR78xl4 and OEM Goodyear C78xl4 Curb Weight .......... 3490 lb./1585 kg Inertia Weight .... 4000 1b./1820 kg Passenger Capacity Five Emi ssi on Contro1 Systern Basic Type ... . Single monolith noble metal catalyst, secondary air injection, EGR5 PCV Mileage on Vehicle ....... 4,940 miles 83 ------- 6. CHASSIS MODEL YEAR/MAKE - 1976 Dodge Aspen Wagon EMISSION CONTROL SYSTEM - Catalyst, EGR Engine Type 4-stroke Otto, OHV, in-line, 6 cyl. Bore x Stroke . . 3.40 x 4.12 in./86 x 105 mm Displacement ........... 225 CID/3687 cc Compression Ratio . , 8.4:1 Maximum Power at rpm 100 hp/75 kW at 3600 rpm Fuel Metering Single one bbl carburetor Fuel Requirement ......... 91 RON unleaded Drive Train Transmission Type 3 speed automatic Final Drive Ratio .. 2.94:1 Chassis Type Unitized body, front engine, rear wheel drive Tire Size OEM Goodyear FR78xl4 and OEM Goodyear E78xl4 Curb Weight 3811 lb/1730 kg Inertia Weight 4000 lb/1820 kg Passenger Capacity . Six Emission Control System Basic Type Dual element monolith noble metal catalyst, EGR, PCV Mileage on Vehicle . 4,360 miles 84 ------- 7. CHASSIS MODEL YEAR/MAKE - 1976 Chevrolet Impala EMISSION CONTROL SYSTEM - Catalyst, EGR Engine Type 4-stroke, Otto cycle, OHV, V-8 Bore x Stroke 4.00 x 3.48 in./101.6 x 88.4 mm Displacement 350 cu. in./5735 cc Compression Ratio 8.5:1 Maximum Power at rpm Fuel Metering Single two bbl carburetor Fuel Requirement 91 RON unleaded Drive Train Transmission Type 3 speed automatic Final Drive Ratio 2.73:1 Chassis Type Body/frame, front engine, rear wheel drive Tire Size OEM Goodrich HR78xl5 and OEM Goodrich H78xl5 Curb Weight 4266 lb./1935 kg Inertia Weight 5000 lb./2270 kg. Passenger Capacity Six Emission Control System Basic Type Single pelletted noble metal catalyst, EGR, EFE, PCV Mileage on Vehicle 4,190 miles 85 ------- 8. CHASSIS MODEL YEAR/MAKE - 1976 Chevrolet Chevette EMISSION CONTROL SYSTEM - Catalyst, EGR, Air Injection Engine Type 4-stroke, Otto cycle, OHV, in-line, 4 cyl. Bore x Stroke 3.23 x 2.61 in. Displacement 58 cu. in./1400 cc Compression Ratio 8.5:1 Maximum Power at rpm 52 hp at 5300 rpm Fuel Metering 1 ME single bbl carburetor Fuel Requirement 91 RON unleaded Drive Train Transmission Type 3 speed automatic Final Drive Ratio Chassis Type Body/frame, front engine, rear wheel drive. Tire Size OEM Goodyear 155/800R13 Curb Weight 1950 lb/1091 kg Inertia Weight 2250 lb/1227 kg Passenger Capacity Four Control System ------- APPENDIX C RESULTS OF FUEL ECONOMY MEASUREMENTS FOR DYNAMOMETER AND TRACK TESTS 87 ------- APPENDIX C RESULTS OF FUEL ECONOMY MEASUREMENTS FOR DYNAMOMETER AND TRACK TESTS LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Honda, CVCC Radial 45 psi Off #1514 LOCATION: Dyno #5 VEHICLE: 76 Honda, CVCC TIRE: Bias 45 psi A/C: Off METER: #1514 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 4 4 2 2 3 3 4 2 2 2 2 2 2 MEAN FUEL ECONOMY 28.02 28.22 32.13 29.13 30.06 40.16 35.83 40.15 40.27 41.30 19.00 33.11 43.39 49.05 42.82 35.68 COV PERCENT* 0.40 1.13 3.33 0.63 0.34 1.43 2.11 1.57 2.87 4.74 4.27 •4.61 2.92 4.52 NUMBER OF REPLICATIONS 3 4 6 3 2 MEAN FUEL ECONOMY 28.11 27.43 31.18 28.50 29.07 40.77 36.40 19.26 33.47 43.82 49.77 43.33 36.14 COV PERCENT* 0.61 2.21 2.26 0.68 0.87 * Coefficient of variation of replicated measurements (standard deviation divided by mean) ------- LOCATION: Dyno #5 and #207 VEHICLE: 76 Datsun TIRE: Radial 45 psi A/C: Off METER: 2099 Corrected + 1514 LOCATION: Dyno #5 and #207 VEHICLE: 76 Datsun TIRE: A/C: METER: Bias 45 psi Off 2099 Correc 1513 Corrected TEST TYPE BAG1 BAG2 BAGS FTP r 1 r (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 3 4 6 4 1 3 3 3 2 2 2 2 2 2 MEAN FUEL ECONOMY 24.62 25.54 28.90 26.16 27.12 37.97 33.61 38.53 37.96 40.69 18.94 29.06 38.92 46.72 41.13 34.66 COV PERCENT* 3.37 1.16 3.03 3.765 1.60 1.87 0.95 0.40 1.36 1.04 -0.06 1.67 0.01 NUMBER OF REPLICATIONS 2 3 3 3 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 25.42 25.92 29.07 26.59 27.40 38.95 34.68 38.21 34.00 19.69 30.33 40.86 48.79 41.10 35.80 COV PERCENT* 0.23 1.80 1.44 1.00 2.58 0.45 1.69 1.62 0.75 0.29 0.42 0.00 0.00 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 89 ------- LOCATION. VEHICLE: TIRE: A/C: METER: LOCATION: Dyno 207 VEHICLE: 76 Datsun TIRE: Bias 45 psi A/C: Simulated METER: Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* NUMBER OF REPLICATIONS 2 2 2 2 MEAN FUEL ECONOMY 25.51 25.16 29.20 26.21 27.06 41.13 COV PERCENT* 0.20 0.37 2.25 0.14 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 90 ------- LOCATION: VEHICLE: TIRE: A/C: METER: Dyno 207 76 Chevette Radial 45 psi Off Unknown LOCATION: Dyno 207 VEHICLE: 76 Chevette TIRE: A/C: METER: Bias 45 psi Off Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 1 1 1 1 1 1 MEAN FUEL ECONOMY 25.94 39.45 34.80 35.11 32.55 28.24 cov PERCENT* NUMBER OF REPLICATIONS 2 2 2 1 MEAN FUEL ECONOMY 19.56 24.26 25.36 23.36 24.78 30.55 COV PERCENT* 0.36 0.44 0.25 1 I i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 91 ------- LOCATION; Dyno #5 VEHICLE: 76 Pinto TIRE: Radial 45 psi A/C: Off METER: 1514 LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Pinto Bias 45 psi Off 1514 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 3 2 2 2 2 2 2 MEAN FUEL ECONOMY 16.50 20.10 21.67 19.59 20.84 27.64 17.05 30.65 33.04 32.32 29.50 25.31 COV PERCENT* 1.03 0.46 1.27 0.63 0.87 2.31 0.94 -0.33 0.55 1.90 NUMBER OF REPLICATIONS 2 5 5 3 3 3 3 1 1 1 1 1 1 MEAN FUEL ECONOMY 16.93 20.86 22.46 20.26 21.61 28.21 COV PERCENT* 0.501 1.76 2.00 1.08 i 1 27.14 27.20 29.18 17.91 31.90 36.04 32.65 30.09 26.12 1.79 1.86 0.43 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 92 ------- LOCATION. VEHICLE: "TIRE: A/C: METER: LOCATION: Dyno #5 VEHICLE: 76 Pacer TIRE: Bias 45 psi A/C: Off METER: 1514 + Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* NUMBER OF REPLICATIONS 2 2 2 3 3 3 3 1 1 1 1 1 MEAN FUEL ECONOMY 13.11 17.26 15.48 15.73 16.38 21.21 20.19 19.73 22.19 17.00 27.07 27.24 25.22 22.54 16.54 COV PERCENT* 6.58 3.44 •4.20 0.38 1 . 83 0.61 i 1.62 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 93 ------- LOCATION. VEHICLE: TIRE: A/C: METER: LOCATION: Dyno #5 VEHICLE: 76 Pacer TIRE: Bias 45 psi A/C: On METER: 1514 TEST TYPE BAG1 BAG2 BAG3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* NUMBER OF REPLICATIONS 2 2 2 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 11.93 15.24 13.86 14.03 14.54 18.94 14.90 23.87 24.62 24.22 21.51 16.23 COV PERCENT* 5.75 1.30 0.15 i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 94 ------- LOCATION. VEHICLE: TIRE: A/C: METER: LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Pacer Bias 45 psi Simulated Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* NUMBER OF REPLICATIONS 1 1 1 2 1 1 1 1 1 1 MEAN FUEL ECONOMY 13.61 17.55 15.20 15.92 16.45 20.88 17.90 27.45 28.56 25.43 22.01 16.65 COV PERCENT* 0.14 ! i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 95 ------- LOCATION; VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Radial 45 psi Off Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Bias 45 psi Off Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 3 3 4 1 3 4 3 1 1 1 1< 1 1 MEAN FUEL ECONOMY 15.07 16.69 17.57 16.54 17.10 22.14 20.36 20.66 20.51 22.94 22.11 29.12 27.29 26.19 24.41 20.83 COV PERCENT* 2.44 3.03 1,88 2.90 1.23 1.42 4.48 NUMBER OF REPLICATIONS 2 3 3 2 1 2 2 3 1 1 1 1 1 1 MEAN FUEL ECONOMY 14.59 16.64 17.33 16.33 16.96 21.61 20.31 20.88 20.46 22.94 18.54 30.44 27.92 26.81 24.71 21.20 COV PERCENT* 8.82 5.19 3.04 i 0.69 2.18 1.83 0.64 i i 1 ! * Coefficient of variation of replicated measurements (standard deviation divided by mean) 96 ------- LOCATION.: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Radial 45 psi On Unknown LOCATION: Dyno #5 VEHICLE: 76 Aspen TIRE: Bias 45 psi A/C: On METER: Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH I ii 1 (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 3 1 1 1 1 1 1 MEAN FUEL ECONOMY 14.1 14.92 16.07 15.03 15.46 20.42 18.40 25.10 24.40 24.58 22.82 18.61 COV PERCENT* 1.60 1.23 0.31 2.50 NUMBER OF REPLICATIONS 1 1 1 1 2 MEAN FUEL ECONOMY 13.50 16.26 17.24 15.82 16.71 19.40 COV PERCENT* 4.01 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 97 ------- LOCATION; VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Radial 26 psi Off Unknown LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 1 1 1 1 1 1 MEAN FUEL ECONOMY 18.55 29.57 29.06 26.42 24.10 20.45 cov PERCENT* NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* I * Coefficient of variation of replicated measurements (standard deviation divided by mean) 98 ------- LOCATION; VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Radial 45 psi Simulated Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Aspen Bias 45 psi Simulated Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 14.78 16.20 17.26 16.14 16.70 22.18 18.30 29.11 26.74 25.49 23.23 19.80 COV PERCENT* 1.10 0.79 0.70 NUMBER OF REPLICATIONS 4 MEAN FUEL ECONOMY 20.32 COV PERCENT* 9.22 i i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 99 ------- LOCATION; VEHICLE: TIRE: A/C: METER: Dyno #5 76 Impala Radial 45 psi Off Unknown LOCATION: Dyno #5 VEHICLE: 76 Impala TIRE: Bias 45 psi A/C: Off METER: Unknown TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph — — — ^^^_— __^_ NUMBER OF REPLICATIONS 2 4 4 3 1 3 3 3 MEAN FUEL ECONOMY 10.62 11.55 13.38 11.77 12.41 18.45 17.22 17.87 18.23 19.07 COV PERCENT* 1.93 0.34 0.47 0.46 2.22 3.33 1.50 NUMBER OF REPLICATIONS 2 2 2 3 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 11.05 11.39 13.54 11.82 12.40 18.78 10.09 18.97 22.87 20.80 20.48 18.40 COV PERCENT* 1.02 0.43 0.57 1.66 1 1 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 100 ------- LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Impala Radial 45 psi Simulated Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Dyno #5 76 Impala Radial 45 psi On 1514 + Unknown TEST TYPE BAG1 BAG2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 2 1 1 1 1 1 1 MEAN FUEL ECONOMY 10.94 11.29 13.10 11.65 12.14 17.68 10.24 19.08 19.69 20.47 19.54 17.54 cov PERCENT* 0.45 1.19 0.70 0.60 NUMBER OF REPLICATIONS 2 2 2 2 i t 1 1 1 1 MEAN FUEL ECONOMY 9.64 10.4,1 12.29 10.67 11.29 16.61 17.61 18.59 17.98 16.15 COV PERCENT* 6.16 0.68 0.46 0.21 t * Coefficient of variation of replicated measurements (standard deviation divided by mean) 101 ------- LOCATION. Track VEHICLE: 76 Honda CVCC TIRE: Radial (24/24 psi) A/C: Off/Windows Up METER: Unknown + 2099 Corrected LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Honda CVCC Bias (24/24 psi) Off/Windows Up 2099 Corrected TEST TYPE BAG1 BAG2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 3 6 5 8 1 2 2 1 2 2 2 2 2 2 MEAN FUEL ECONOMY 24.96 25.41 28.81 26.14 27.01 35.92 32.56 34.65 34.48 38.10 50.01 50.29 45.55 40.17 34.21 28.05 cov PERCENT* 1.75 1.76 0.78 2.77 1.08 0.86 0.65 2.97 2.00 0.65 0.76 1.16 NUMBER OF REPLICATIONS 2 3 3 2 3 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 23.61 25.49 29.35 25.98 27.17 35.51 34.93 34.18 37.02 47.01 47.68 36.91 32.16 27.28 21.12 COV PERCENT* 5.93 0.60 3.55 1.29 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 102 ------- LOCATION. Track VEHICLE: 76 Honda CVCC TIRE: Radial (24/24 psi) A/C: Off/Windows Down METER: Unknown LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAG3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 2 2 2 MEAN FUEL ECONOMY 52.01 50.90 46.65 41.86 35.72 29.47 COV PERCENT* 2.35 3.10 2.90 1.37 0.48 0.17 NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* i i i i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 103 ------- LOCATION. Track LOCATION: Track VEHICLE: Datsun TIRE: Radial (24/24 psi) A/C: Off/Windows Up METER: #1472 VEHICLE: TIRE: A/C: METER: Datsun Bias (24/24 ps-j) Off/Windows Up #1472 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 4 9 5 6 4 3 3 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 23.78 24.60 27.54 25.14 25.98 36.76 35.40 34.38 38.48 18.48 28.94 39.50 45.58 40.18 34.81 29.69 24.96 cov PERCENT* 3.46 1.48 1.21 1.41 1.98 1.36 2.68 1.11 0.54 0.52 0.34 0.67 0.02 0.29 4.08 NUMBER OF REPLICATIONS 1 4 3 3 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 21.76 23.65 26.15 23.83 24.83 35.56 18.51 28.68 38.35 44.12 38.83 38.14 29. 3-6 24.31 COV PERCENT* 4.82 2.88 3.04 i 1.64 1.65 1.00 1.70 1.51 0.06 0.02 0.26 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 104 ------- LOCATION. Track LOCATION: Track VEHICLE: 76 Chevette TIRE: Radial (24/24 psi) A/C: Off/Windows Up METER: #1472 VEHICLE: TIRE: A/C: METER: 76 Chevette Bias (24/24 psi) Off/Windows Up #1472 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 7 7 7 1 2 2 2 2 2 2 1 2 2 MEAN FUEL ECONOMY 17.68 22.09 23.51 21.32 22.76 26.69 21.47 25.07 25.66 28.05 35.88 34.33 32.16 28.85 23.59 20.09 cov PERCENT* 0.32 4.20 6.71 0.64 1.86 0.03 0.30 2.35 5.48 0.88 5.10 2.92 NUMBER OF REPLICATIONS 2 2 2 1 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 17.20 21.74 22.18 20.70 21.95 26.11 25.20 25.18 27.71 33.44 30.98 30.52 28.49 23.87 18.88 COV PERCENT* 1.69 1.30 2.55 0.36 0.81 0.77 3.98 3.72 2.76 1.91 1.78 i 9.62 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 105 ------- LOCATION. VEHICLE: TIRE: A/C: METER: Track 76 Chevette Radial (24/24 psi) Off/Windows Down #1472 LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAG3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 1 1 2 2 MEAN FUEL ECONOMY 27.20 35.05 30.63 30.46 28.55 24.29 20.05 cov PERCENT* 1.14 5.61 2.26 1.51 0.21 NUMBER OF REPLICATIONS 1 MEAN FUEL ECONOMY COV PERCENT* i i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 106 ------- LOCATION. Track VEHICLE: 76 Chevette TIRE: Radial (24/24 psi) A/C: On/Windows Up METER: #1472 LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 16.35 20.12 20.82 19.36 20.45 25.42 31.51 30.69 29.74 27.94 23.72 19.52 cov PERCENT* 0.16 1.09 1.05 0.36 4.76 2.79 3.45 1.59 2.71 1.09 NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* 1 1 1 1 | 1 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 107 ------- LOCATION. Track VEHICLE: 76 Pinto TIRE: Radial (24/24 psi) A/C: Off/Windows Up METER: 1513 Corrected + Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Pinto Bias (26/26 psi) Off /Windows Up 1514 + Unknown TEST TYPE BAG1 BAG-2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 5 3 2 1 . 1 1 1 1 i 1 i 1 MEAN FUEL ECONOMY 16.63 19.06 1-9.64 18.64 19.33 26.01 21.43 18.72 29.97 31.78 30.08 28.23 24.64 20.99 16.26 COV PERCENT* 11.95 1.58 0.10 2.47 NUMBER OF REPLICATIONS 1 3 2 1 2 2 3 3 2 MEAN FUEL ECONOMY 16.11 18.75 19.49 18.31 19.09 25.03 21.92 24.55 24.41 27.53 COV PERCENT* 3.10 6.31 3.08 1 4.46 2.23 2.22 2.13 i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 108 ------- LOCATION. VEHICLE: TIRE: A/C: METER: Track 76 Pacer Radial (24/24 psi) Off/Windows Up 1514 LOCATION: Track VEHICLE: TIRE: A/C: METER: 76 Pacer Bias (26/24 psi) Off/Windows Up 1514 TEST TYPE BAG1 BAG2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 2 1 1 1 1 1 MEAN FUEL ECONOMY 17.04 14.78 15.98 18.99 16.62 17.62 17.12 18.14 COV PERCENT* 3.82 1.20 NUMBER OF REPLICATIONS 1 1 1 2 MEAN FUEL ECONOMY 16.21 15.24 15.74 19.00 16.22 COV PERCENT* 1.66 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 109 ------- LOCATION. VEHICLE: TIRE: A/C: METER: Track 76 Pacer Radial (24/24 psl) Off/Windows Up 1358 LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAG 3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 4 2 1 1 2 2 1 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 12.69 15.10 15.00 14.50 15.05 17.88 16.70 17.67 17.47 20.04 33.16 29.87 25.43 21.66 16.29 14.11 12.45 cov PERCENT* 0.28 3.72 2.26 1.40 0.36 4.50 3.53 4.73 3.46 6.64 0.25 0.17 NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* * Coefficient of variation of replicated measurements (standard deviation divided by mean) 110 ------- LOCATION. VEHICLE: TIRE: A/C: METER: LOCATION: Track VEHICLE: 76 Pacer TIRE: Bias (26/24 psi) A/C: On/Windows Up METER: 1513 Corrected + 1514 TEST TYPE BAG1 BAG2. BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* NUMBER OF REPLICATIONS 2 5 3 3 1 1 1 1 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 11.71 14.05 13.21 13.27 13.64 16.47 16.20 15.39 16.70 19.53 27.00 25.49 23.51 20.72 15.77 13.88 11.62 COV PERCENT* 2.85 0.89 6.16 5.49 i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 111 ------- LOCATION. Track VEHICLE: 76 Pacer TIRE: Radial (24/24 psi) A/C: On/Windows Up METER: 1358 LOCATION: VEHICLE: TIRE: A/C: METER: TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 1 3 2 1 2 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 12.15 14.60 13.60 13.75 14.14 16.39 16.51 16.66 18.46 28.10 27.27 24.20 20.48 15.63 14.09 11.80 COV PERCENT* 2.18 4.78 0.21 0.04 0.50 1.38 0.16 0.26 0.66 0.32 0.35 2.70 NUMBER OF REPLICATIONS MEAN FUEL ECONOMY COV PERCENT* i 1 i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 112 ------- LOCATION. Track VEHICLE: 76 Aspen TIRE: Radial (26/32 psi) A/C: Off/Windows Up METER: 1514 LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Aspen Bias (26/32 psi) Off/Windows Up 1514 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 3 6 3 4 1 3 4 4 MEAN FUEL ECONOMY 13.70 15.17 16.48 15.15 15.79 20.77 19.33 19.62 20.19 21.78 21.88 29.39 28.97 25.66 24.03 20.97 cov PERCENT* 3.59 1.41 2.88 2.79 1.38 1.16 3.73 NUMBER OF REPLICATIONS 1 5 4 3 2 2 2 2 2 2 MEAN FUEL ECONOMY 12.38 14.71 15.47 14.33 15.06 19.90 COV PERCENT* 0.98 2.80 2.71 I I 22.48 27.24 26.97 24.39 22.10 19.89 ! 1 1.48 2.05 0.60 0.20 i 1.31 1.03 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 113 ------- LOCATION. Track VEHICLE: 76 Aspen TIRE: Radial (26psi/32psi) A/C: On/Windows Up METER: 1514 LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Aspen Bias (26psi/32psi) On/Windows Up 1514 TEST TYPE BAG1 BAG 2 BAG3 FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 4 2 3 2 2 2 2 2 2 MEAN FUEL ECONOMY 12.69 13.69 15.84 13.97 14.70 19.56 21.22 25.28 25.79 24.15 22.20 19.93 COV PERCENT* 0.72 6.32 0.312 4.25 NUMBER OF REPLICATIONS 2 2 2 3 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 13.37 14.80 14.01 18.74 COV PERCENT* 2.75 3.87 2.44 i 19.18 23.86 23.98 22.74 20.86 18.80 15.91 13.63 I 4.76 1.72 1.15 0.44 0.44 1.73 0.89 1.40 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 114 ------- LOCATION. Track VEHICLE: 76 Ford Granada TIRE: Radial (25/25 psi) A/C: Off/Windows Up METER: 1514 + Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Ford Granada Bias (25/25 psi) Off/Windows Up 1514 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 6 4 3 3 1 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 11.66 14.34 14.77 13.78 14.54 18.33 16.99 19.98 26.40 25.63 23.14 20.88 18.03 14.49 10.91 cov PERCENT* 4.49 4.82 3.95 NUMBER OF REPLICATIONS 2 7 5 3 2 1 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 14.58 14.79 14.08 14.68 17.81 15.89 18.11 25.49 25.39 22.78 20.95 17.73 14.11 11.00 COV PERCENT* 1.93 1.69 0.59 5.43 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 115 ------- LOCATION. Track VEHICLE: 76 Ford Granada TIRE: Radial (25/25 psi) A/C: On/Windows Up METER: 1514 + Unknown LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Ford Granada Bias (25/25 psi) On/Windows Up 1514 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 5 3 3 1 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 10.14 12.14 12.39 11.72 12.26 16.49 18.99 21.75 22.21 20.48 18.59 16.12 12.68 10.78 cov PERCENT* 0.56 1.94 2.33 NUMBER OF REPLICATIONS 2 5 3 2 1 1 1 1 1 MEAN FUEL ECONOMY 11.14 12.28 12.88 12.17 12.56 15.94 20.09 18.10 15.84 12.38 10.79 COV PERCENT* 2.66 8.04 3.52 * Coefficient of variation of replicated measurements (standard deviation divided by mean) 116 ------- LOCATION. Track VEHICLE: 76 Impala TIRE: Radial (26/28 psi) A/C: Off/Windows Up METER: 1472 LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Impala Bias (26/28 psi) Off/Windows Up 1472 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 7 5 3 1 3 3 3 1 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 10.75 11.70 13.29 11.86 12.45 17.59 16.48 17.32 17.50 18.84 8.83 17.63 20.15 20.14 19.81 18.12 15.94 13.93 cov PERCENT* 5.20 3.89 4.09 7.18 1.07 0.16 0.88 2.41 3.68 0.91 0.96 0.98 0.93 0.25 NUMBER OF REPLICATIONS 3 6 3 3 3 1 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 9.65 10.76 12.35 10.88 11.50 17.16 11.81 17.65 19.22 19.45 19.29 17.69 15.48 13.30 COV PERCENT* 1.71 1.09 1.68 2.19 i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 117 ------- LOCATION. VEHICLE: TIRE: A/C: METER: Track 76 Impala Radial (26/28ps1) On/Windows Up 1472 LOCATION: VEHICLE: TIRE: A/C: METER: Track 76 Impala Bias (26/28psi) On/Windows Up 1472 TEST TYPE BAG1 BAG2 BAGS FTP (Derived) HH (Derived) HST CST HNO HRE HSM 10 mph 20 mph 30 mph 40 mph 50 mph 60 mph 70 mph 80 mph NUMBER OF REPLICATIONS 2 4 2 2 2 2 2 2 2 2 2 2 MEAN FUEL ECONOMY 10.18 10.54 12.27 10.87 11.35 16.86 9.85 14.62 17.48 18.13 18.53 16.47 14.99 13.19 cov PERCENT* 3.06 2.16 3.63 0.34 0.72 6.92 0.53 1.68 0.50 3.13 2.08 0.96 NUMBER OF REPLICATIONS 3 5 2 1 1 1 1 1 1 1 1 1 MEAN FUEL ECONOMY 9.39 9.96 11.56 10.21 10.71 16.20 9.85 13.57 16.95 18.28 17.94 16.66 14.66 12.97 COV PERCENT* 1.35 1.37 2.26 i i i | i * Coefficient of variation of replicated measurements (standard deviation divided by mean) 118 ------- APPENDIX D WEIGHTED LEAST SQUARES LINEAR REGRESSION OF VOLUMETRIC AND CARBON BALANCE DIFFERENCES Let x.j , y.j be volumetric and carbon balance measures, respectively for the ith group of replicated runs, and let n-j be the number of replications. Two different types of measures may be considered, namely, mean fuel consumption (in gpm) or mean fuel economy (in mpg) of the replicated runs, but the regression technique is the same in either case. Define A^ = y^ - x^ , the difference between volumetric and carbon balance measures, and assume a linear model for the dependence of A on x. That is, A. = a + bx. + e. i i i where a and b are unknown constants to be estimated and e^ is an error of zero mean and variance given by „ ni It is assumed here that the variabilities of a single carbon balance measurement and of a single volumetric measurement are expressed by constant coefficients of variation, (COV)C and (COV)M, respectively, and that (COV)02= (COV)C2 + (COV)M2 is the (squared) coefficient of variation of an unreplicated difference A relative to the mean of either measure. From this, it follows that as shown above, the variance of e-j (the error in Aj ) is (COV)g2 multiplied by the squared mean (approximately x^) to convert to variance, and then divided by rii to reflect the variance reduction derived from replication. Because the ae-j2 are not uniform over the data set, those points with smaller variance should receive relatively higher weight in estima- tion of a regression line. The appropriate weighting is proportional to the inverse of the variance. Thus, define normalized weights as follows: 119 ------- u. . V*,' . ", i z n./x,2 " x.2U J J I The estimation of a and b by least (sum of weighted) squares regression is based on the following statistics: A *= Z u.A. l i l A2 = Z u.A.2 l l X = Z U.X. X2 = Z U.X.2 A • x = Z u.A.x. i Weighted least squares estimates for a and b may then be expressed as x - A x x2 - (x): a = A - b x In order to assess the significance of the coefficient values so derived, their variance also needs to be estimated. To do this we need an estimate for (COV)Q, which is given by = [A2 - (A)2 - (b)2 (x2 - (x)2)] U where N is the number of data points (i.e., replication groups). The S\ "^ variance of a and b are then a.2 - (COVV a u (COV) 2 b U (x2 - (x)2) J2Q ------- APPENDIX E TWO-WAY ANALYSIS OF VARIANCE WITH UNEQUAL VARIANCE ESTIMATES Let us suppose we have sample means y-y and estimated variances s.j .2 of a response variable for various combinations of blocks (i = 1, 2, ..., I) and treatments (j = 1, 2, ..., J). We desire to know if there are significant effects due to blocks and/or treatments. This situation is different from a conventional Analysis of Variance (ANOVA) situation in that we do not have available individual responses within each (i,j) cell, but rather a cell mean and an associated variance. However, there is a very strong similarity with the 2-way ANOVA model with unequal numbers* and the formulas derived will be seen to be analogs of that model. For applications made in this report, the y^ are mean fuel economy ratios, the sij2 are squared standard error estimates, and the blocks and treatment groups may cover such factors as different test cars, air conditioning status, and different test driving sequences. Responses are generally available for only a subset of all (i,j). However, there must be at least one response for each block and for each treatment and, if N is the total number of cells for which responses are available, N >_ I + J - 1. The model assumed is a two-way effects model with no interaction: y"T7 = u + b. + t. + e.. •Mj M i J iJ where e^ . are independent normal errors with zero mean and variance, s.j-2. Th^ quantity y is the (weighted) grand mean over all available responses and the b-j (and t,-j are systematic effects due to particular blocks (and particular treatments). We desire to test certain hypothesis, notably and H : b. = b, i.e., there are no differential effects among blocks b i H : t. = t, i.e., there are no differential effects among treatments t J * See, for example, 0. Kempthorne, The Design and Analysis of Experiments, John Wiley, New York, 1952, p. 79. 121 ------- Define weighting coefficients „ - N / Z 1 1' • • 9/11 o 1J Sij / kJ Skl utilizing the convention that 1/s-jj = 0 for all non-response (i,,ij) cells, Note, therefore that n. =0 for all non-response (ij) and Zn. . = N Define N, = Z n. . N = Z n.. V< U 'Vj i IJ Y. = Z n.. y.. V = Z n. . y. 1.- . U U Y.j . U ^i J I = I n.. y. . Impose the two conditions Z N. b. = Z N . t. = 0 i* i -J J on the model because of linear dependences of the coefficients. This says that the weighted average block effect over all blocks is constrained to zero and the weighted average treatment effect over all treatments is constrainted to zero, therby defining an unambiguous grand mean effect y. Weighted least squares estimates of the coefficients, y, b., t., are next obtained. The grand mean estimate is computed first 122 ------- Define the column vectors X = (b1,b2,...,bI_1,t1,t2>...,tJ_1) C= (Y1.-N1.y,...5YI_lj.-NI_1.u5Y.1- and the I+J-2 order square matrix N. 0 1- 1-1- V. . 1J A. . 1J 'N. N . 0 •1 •. J-1* / i = 1, ..., 1-1 j = I, ..., I+J-1 i = I, ..., I+J-1 j = 1, ..., 1-1 Solve the matrix equation y\.X = C for X, i.e., X =yV C /V /% / This provides all the b. except bj and all the tj except tj. Solve for bj and tj from the previously imposed constraints. The reduction in Sum of Squares (S.S,) due to fitting y, b-j is R(y,b) = ; I degrees of freedom (d.f.) 123 ------- Similarly, the reduction in S.S. due to fitting y,t, is J J - R(y,t) = y - r - ; J degrees of freedom (d.f.) T-:- J=l Finally, the reduction in S.S. due to fitting all parameters, y.b^tj is R(y,b,t) = y Y + £ b. Y. + Z t. Y . ; (I+J-1) d.f. j i i* • J *J For testing hypothesis H. : b. ~ b R(y,b,t) - R(y,t) Mean square due to fitting bn- : s = - —•> - Mean square error: E = — - ; d.f. > > 1* Under H. , S/E has approximately F-distribution with (1-1,°°) degrees of freedom. Therefore, for tests at a level of significance a, reject H. if S/E > f. . b I-l,°°,a For testing hypothesis H : t. = t _^___ J R(y,b,t) - R(y,b) Mean square due to fitting t. : T = — j o-J. Mean square error: E = —. ; d.f. > > 1* 77 E 1 / S..2 N .. ij Under H., T/E has approximately F-distribution with (J-l,°°) degrees of freedom. Therefore, for tests at a level of significance a, reject Ht if T/E > f, . L - * Note, in contradistinction to conventional ANOVA, the mean square error is estimated (externally) from the S-jj2, rather than from the variations of y-jj among the block/treatment cells, because of the considerably greater degrees of freedom in the external estimate. 124 ------- APPENDIX F CALCULATION OF HORSEPOWER FROM COAST-DOWN TIMES If the time, At, it takes a vehicle of mass, M, to decelerate from 55 mph to 45 mph is measured in seconds, then the force acting on the vehicle at 50 mph is estimated to be F is in units of pounds if M is in units of slugs, Av in units of feet per second and At in units of seconds. The power dissipated by the vehicle at speed VT is P = FVT where P is in units of ft-lbs/min if Vy is in units of ft/min. V = 50 mph = 4400 ft/min Av = 10 mph = 14.667 ft/sec Thus, M '14'667 n /je 1L, . . 32.16 Ib/sli P (ft-lb/nrrn) =— — and n i*>. TI_/ • \ Mass of vehicle in Ib /onn,- -7 r* / • \ P (ft-lb/min) = 7 -—. — : — (2006.7 ft sec/min v ' ' Coast-down time in seconds v n /i, \ Mass of vehicle in Ib /n neno1» P (Horsepower) = -—, r-: : r—J 0.06081) v Coast-down time in seconds) since 1 ft-lb _ 1 horsepower min ~ 33,000 125 ------- |