MC 76-10
Technical Support Report
Effect of Driver Mass Tolerance on
Motorcycle Emissions and Fuel Economy
November 1976
Notice
Technical support reports for regulatory action do not necessarily
represent the final EPA decision on regulatory issues. They are intended
to present a technical analysis of an issue and recommendations resulting
from the assumptions and constraints of that analysis. Agency policy
constraints or data received subsequent to the date of release of this
report may alter the conclusions reached. Readers are cautioned to seek
the latest analysis from EPA before using the information contained
herein.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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Abstract
Motorcycle emissions and fuel economy were measured as driver mass was
varied. Compared to tha specified driver mass (80 kg), significant
differences in emissions and fuel economy were first observed when the
mass was varied + 10 kg from the specified mass.
Prepared by
Approved By: Project
Manager, Motorcycle
Regulations
'
Approved By: ,
Branch Chief,
Standards Development
and Support Branch
'Approved By:
)ivision Director,
Emission Control Technology
Division
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-1-
Introduction
In developing the motorcycle regulations, two factors were considered
when the driver mass tolerance was specified for emission testing.
First, by specifying a restrictive tolerance, too many potential test
drivers might be excluded. But, by specifying a broad tolerance, wide
variations in emissions results were considered possible. Therefore, to
accommodate both of these factors, the tolerance was specified as
+ 10 kg.
To determine the appropriateness of this tolerance prior to final rule
making, a test program was conducted to measure emissions and fuel
economy at various driver masses. The test vehicle used was a Honda
CB360 which represents a typical middle weight, four stroke motorcycle.
Summary and Conclusions
Based on the results of these tests the tolerance of + 10 kg is an
appropriate driver mass tolerance for emission testing.
Trends' of increasing HC, CO, and C02 and decreasing fuel economy were
observed as driver mass was increased from about 60 to 120 kg. Though
these emissions, fuel economy, and bag 1 NO correlated well with
driver mass, bag 2 NO emissions were very low in concentration and
difficult to accurately measure, and did not correlate well, while
composite NO just missed correlating.
X
Discussion
A. Test Objective
The objective of this testing program was to determine the appropriateness
with respect to emissions of the driver mass tolerance specified in
§86.529(c)(1) of the motorcycle regulations.
To accomplish this emissions' measurements were made on a Honda CB 360
while driven over the Urban Dynamometer Driving Schedule. The test
procedure with exceptions noted below were in accordance with the Federal
Test Procedure. Nominal driver masses of 60, 70, 80, 90, 100, and 120
kg were tested where 80 kg is the specified nominal driver mass setting.
To eliminate variations due to different drivers, such as in expertise,
capability, and degree of training, the same driver was used throughout
the testing sequence. Additional mass was centered directly underneath
the driver to attain the higher mass settings. To obtain rep^eatable
results and minimize test time, only hot start bag 1 and 2 tests xvere
conducted. This was repeated three times at each driver mass setting.
* A significance level of .05 was used in these determinations. This
same significance level is implicit in all subsequent references to
trend and differences throughout this report.
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—2—
B. Effect of Driver Mass
Figure 1 shows the results of this study plotted against nominal driver
mass. These plots are not sufficient to reveal with confidence the
relationship between emissions and driver mass.
To determine the relationship between emissions (and fuel economy) and
driver mass, a linear regression analysis was performed. Using the mean
emissions and fuel economy results at each driver mass, the regression
equation has the form:
Emissions = a + a.. (Driver Mass)
where a is the y-intercept and a., is the slope of the regression line.
Table 1 presents the effects on emissions and fuel economy of varying
driver mass. Only those data displaying sufficient correlation are
presented. Table 2 presents actual correlation coefficients which
should be considered when interpreting these results. HC, CO, and ,CO?
increased while fuel economy decreased with increasing driver mass and
displayed good correlation. NO did- not quite show sufficient correlation
on a composite basis. (Bag 1 results correlated well, however, bag 2
results did not. This may have been due to the difficulty in measuring
the low bag 2 concentrations of NO .)
X
After determining the relationships between emissions and driver mass,
it was necessary to determine the extent to which driver mass could be
varied from the specified driver mass before significant differences in
emissions would be observed. To do this, an analysis of variance
of emission results was performed. This is described by the following:
80 DM is distributed as a t-statistic where:
sA <
"80
Xo~ is the mean emissions at a driver mass of 80 kg
x , is the mean emissions at the driver mass to be compared-
s is the pooled standard deviation and is equal to:
8080 "1) + SDM(nDM
n80 + nDM - 2
non> nr.M are tne number of test points at each driver mass,
oU JJM . -
respectively
Using tables with the percentage points of the t-distribution, the level
of significance of the comparison can be determined. Differences in
emissions were considered significant at a significance level of about
.05 or below.
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5-
4'
3-
1
Q
50
X
X
..x P 40
* ^
• "° 30
i
2C
o
o
1C
0
* x x
X
Figure 1
1
Effects of Driver Mass on
Motorcycle Emissions
and Fuel Economy
- Composite emissions from
Bag 1 & 2 hot start tests.
0 20 40 60 80 100 120 0 20 40 60 80 100 120 _ Test vehicle - Honda CB36C
Nominal Driver Mass - kg Nominal Driver Mass - kg
.07
.06
50
40
o 30
> i i-
X
X X
X X
^
x _5
! 20 f
X
^ * X X
§ 15 -
c
o
CJ
w 10-
i— i
a)
3
fe 5 ••
,,--.,t ..... i . ,> i 1 \ 1 1- . i . i — . » • i 0 ' .a-—, ,i .— >-^ t . i i . i 1 ....J , - . t . .1 ... :,
0 20 40 60 80 100 120
Nominal Driver Mass - kg
0 20 40 60 SO 100 120
Nominal Driver Mass - kg
0 20 40 60 80 100 120
Nominal Driver Mass - kg
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TABLE 1
Comparison Between Predicted Values Using Regression Equation and Actual Mean Emissions
Nominal
Driver
Mass, kg
60
70
80
90
100
120
H C , g/km
Kop.r.
Eqr. .
Fred.
3.88
4.02
4.15
4.29
4.42
4.69
7 *^- F
/• l/^i. •
from
80 kg
-6.5
-3.1
+3.5
+6.6
+13.1
Actual
Test
Mean
3.81
3.95
4.24
4.41
4.23
4.61
% Dif.
from
80 kg
-10.1
-6.8
+4.0
-0.2
+8.7
C 0 , g/km
Regr.
Eqn.
Fred.
44.6
45.7
46.6
47.6
48.6
50.6
% Dif.
from
80 kg
-4.3
-2.0
+2.2
+4.3
+8.6
Actual
Test
Mean
43.3
45.9
43.0
48.3
48.4
49.9
% Dif.
from
SO kg
-9.8
-4.4
+0.6
+0.8
+4.0
C 0 2 , g/km
Regr.
Eqn.
Fred.
46.9
47.6
48.1
48.8
49.3
50.5
% Dif.
from
80 kg.
-2.4
-1.1
+1.3
+2.5
+5.0
Actual
Test
Mean
45.8
48.3
48.9
48.7
49.4
50.1
7, Dif.
from
80 kg
-6.3
-1.2
-0.4
+1.0
+2.5
NO., g/km
(1)
FUEL ECONOMY g/litre
Regr.
Eqn.
Fred.
18.1
17.8
17.5
17.1
16.8
16.1
% Dif.
from
80 kg
+3.8
+1.8
-2.0
-3.8
-7.6
Actual
Test
Mean
18.6
17.6
17.0
16.9
16.9
16.4
% Dif.
from
80 kg
+9.4
+3.5
-0.6
-0.6
-3.5
(1) Insufficient correlation at a 95% confidence level to allow prediction.
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-5-
TABLE 2
Driver Mass Regression Statistics
Bag
1
Bag
2
Com-
posite
r
r rcq'd for
95% conf. level
Signif. 0 95%?
r
r rcq'd for
95% conf. levc!
signif. @ 95%?
r
r req'd for
95% conf. level
SigniC. @ 95%?
HC
.9263
+ .8114
yes
.8390
+ .8111
yes
.9194
+ .8114
yes
CO
.9328
+ .8114
yes
.8797
+ .8114
yes
.9102
+ .8114
yes
co2
.8886
+ .8114
yes
.8525
+ .8114
yes
.8755
+ .8114
yes
NO
X
.8191
±. 8114
yes
.6822
+ .8114
no
.7636
+ .8114
no
Fuel
Economy
-.9194
+ .8114
yes
-.9169
+ .8114
yes
-.9036
+ .8114
yes
Hypothesis Tests of the Slope of the Regression Lines
(H : slope
0)
Bag
1
Bag
2
Com-
pos i.ic
slope
L-test
sipnif. level
reject 1! :
slope = 0?
slope
t-tust
signif. level
reject H :
slope = 0?
slope
t-test
signif. level
reject II :
slope = 0?
H C
.0119
.0079
yes
.0136
.0178
yes
.0128
.0095
yes
C 0
.1000
.0066
yes
.0139
.0208
yes
.1021
.0117
yes
co2
.0565
.0179
yes
.0652
.0310
yes
.0612
.0223
yes
N0x
2.46 x 10"4
.0461
yes
1.49 x 10"4
.1354
no
1.89 x 10~4
.0772
no
Fuel
Economy
-3.53 x 10"2
.0095
yes
-2.52 x 10~2
.0101
yes
-3.40 x 10"2
.0135
yes
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Table 3 presents significance levels for comparisons of all driver
masses. In figure 2 the shaded areas show where significant differences
are first observed as driver mass is allowed to vary from the specified
mass of 80 kg. For HC these differences occur almost exactly at +10 kg.
For CO, C0_, and fuel economy differences are first observed as shown in
Figure 2, however a review of the significance levels in Table 3
Region where significant differences were
first observed at a significance level of .05
mass
spec +i^\\H-20\N
-20 "\\~10 spec +10 +20
\N ™ass
! (80kg)
\\~20 -10 spec +10 +20
\\ ] mass
(30kg)
\-20\\-10 spec +1Q +20
\ \\\N mass
(8Qkg)
-1-40
Figure 2
indicates that differences reach significance somewhat before the
shaded areas indicate. No data were taken to show exactly where these
differences become significant.
C. Physical Interpretation of the Effect of Driver Mass
1 2
For passenger car tires, it has been fairly well established ' that as
vertical load increases (decreases) the rolling resistance of bias ply
tires also increases (decreases). Although this has not been shown to
be true specifically for motorcycle tires, these tires are also of the
bias ply type and it seems reasonable that they xrould behave in a
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TABLE 3
Significance Levels — T-test of Mean Emission at Various Driver Masses
69.3
78.4
83.7
93.1
117.5
69.3
73.4
33.7
98.1
117.5
69.3
78.4
88.7
98.1
117 . 5
69.3
78.4
S3. 7
98.1
117.5
.0337
.0002
.0002
.0003
.0000
59.0
.0158
.0003
.0002
.0009
.0001
59.0
.1060
.0416
.0319
.0364
.0150
59.0
.0132
.0076
.0092
.0181
.0052
.0225
.0029
.0093
.0008
69.3
.0007
.0005
.0059
.0003
69.3
.4905
.3509
.3770
.0704
69.3
.1024
.2508
.1971
.0335
HC
Bag 1
.0116
.1342 .0664
.0013 .0842 .0056
78.4 88.7 98.1
CO
.0061 Bas l
.0805 .9442
.0011 .0161 .0690
78.4 88.7 98.1
C°2
Bag 1
.6221
.6854 .9207 •
.0643 .0635 .1022
78.4 88.7 98.1
NO
X
.2302 — Bag *
.4199 .2670
.1365 .0495 .9378
69.3
78.4
88.7
98.1
117.5
69.3
78.4
88.7
98.1
:T. :*f. 11?-5 n
69.3
••'78.4
88.7
. 98.1
117.5
69.3
78.4
88.7
98.1
117.5
.6581
.1131 .0672
.0541 .0164
.1864 .1366
.0206 .0060
59.0 69.3
.0971
.0113 .0009
.0161 .0033
.0130 .0006
.0056 .0006
59.0 69.3
.0204
.0198 .3752
.0209 .7058
.0052 .0216
.0067 .0413
59.0 69.3
.1246
.1346 .3739
.1959 .4918
.0673 .1929
.1071 .3739
.2532
.3585
.0294
78.4
.2203
.2666
.0248
78.4
.5634
.2833
.2224
78.4
.5946
.1688
.1583
HC
Bag 2
.0353
.0410 .0086
88.7 98.1
CO
Bag 2
.4979
.0130 .0096
88.7 98.1
co2
Bag 2
.0648
.0769 .6126
83.7 98.1
NO
X
Bag 2 .
.1552
-.3349 .2511
69.3
78.4
88.7
98.1
117.5
69.3
78.4
88.7
98.1
117.5
69.3
78.4
88.7
98.1
117.5
69.3
78.4
88.7
98.1
117.5
.3630
.0254 .0476
.0057 .0063
.0218 .0384
.0026 .0026
59.0 69.3
.0067
.0007 .0001
.0007 .0004
.0007 .0006
.0002 .0000
59.0 69.3
.0224
.0064 .2852
.0085 .4483
.0046 .1016
.0022 .0219
59.0 69.3
.0426
.0325 .2879
.0495 .7676
.0259 .1462
.0206 .0668
.0600
.8588
.0097
78.4
.3310
.2369
.0005
78.4
.6247
.2231
. 0215
78.4
.2746
.2174
.1550
HC
Composite
.0163
.0306 .0040
88.7 98.1
Composite
.7116
.0027 .0064
88.7 98.1
co2
Composite
.1489
.0182 .1282
88.7 98.1
Composite
.1355
.0697 .5593
59.0 69.3 78.4 88.7 98.1
59.0 69.3 . 78.4 88.7 98.1
59.0 69.3 78.4 88.7 98.1
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similar manner. Thus, the increased vertical load increases the power
required to move the vehicle at a given speed. This requires greater
throttle openings thereby increasing the mass flow of air-fuel mixture
into the engine. Since the air-fuel ratio did not change significantly*,
the greater throttle opening has the effect of increasing the mass of
emissions and fuel consumption which was substantiated by the data in
this study.
D. Applicability to Other Motorcycles
The results of this study should be applicable to other motorcycles on
a general basis. To overcome added load, it is necessary for all
motorcycles to increase throttle opening which will increase their mass
emissions and fuel consumption. This effect may be more dramatic for
smaller motorcycles and somewhat less noticable for larger ones, however,
the aggregate effect would be expected to be similar to that shown by
this study.
E. Recommendations
These tests revealed that emissions and fuel economy become significantly
different as driver mass deviates by about 10 kg from the specified
value of 80 kg. Because a restrictive tolerance would exclude many
potential drivers, and a broad tolerance will significantly affect
emissions and fuel economy results, it is recommended that the driver
mass tolerance be + 10 kg.
* These results are not shown because of their approximate nature.
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References
1. Willet, P.R., "Hysteretic Losses in Rolling Tires," Rubber,
Chemistry, and Technology, Vol. 46, No. 2, pg 425-441 (1973).
2. Schuring, D.J., "Rolling Resistance of Tires Measured Under Transient
and Equilibrium Conditions on Calspan's Tire Research Facility,"
Dept. of Transportation Report No. DOT-TSC-OST-76-9, pg 69-71
(March 1976)
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