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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWOOD ROAD

ANN ARBOR, MI 48105-2498

 OFFICE OF

AIR AND RADIATION

May 11, 2015

MEMORANDUM

SUBJECT: Vocational Vehicle Tire Rolling Resistance Test Data Evaluation

FROM: Lauren Steele, Environmental Engineer, OTAQ/ASD

TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Mediumand Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-

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Introduction

This memorandum presents available information on the range of coefficients of rolling 

resistance (CRR) of tires that are manufactured for vocational vehicle applications. These were 

identified by the manufacturer’s description of intended vehicle application specified when the 

tire was obtained for testing. Tires with applications listed exclusively as “line haul”, “long 

haul,” or “trailer” were excluded from this analysis and are not presented here. Tires with 

applications that included “bucket truck”, “bus”, “city delivery”, “construction”, “high scrub”,

“intercity coach”, “local P&D”, “mixed service”, “on/off road”, “on/off highway”, “regional”, 

“RV”, “refuse”, “school bus”, “short haul,” and “special service” have all been included in this 

analysis. Throughout this document, these tires are referred to as vocational tires, though this is 

solely based on these descriptors indicating intended application, not on any declaration from a 

manufacturer.

Among the descriptors provided with each tire that was tested is a load rating. These data 

include tires with load ratings of F, G, H, J, L, L2, and M, representing tires designed to support 

increasingly greater loads, given appropriate inflation pressure. Commercial truck tires typically 

have lookup tables for acceptable loads across a range of inflation pressures, however the 

agencies’ official test procedure for measuring CRR (ISO 28580) specifies that testing conditions 

must be with the tire loaded to 85% of its maximum load capacity, at an inflation pressure as 

specified corresponding to 85% of maximum load capacity. With these standard test conditions, 

the effects on CRR of tires of different load capacities are neutralized. Therefore, the 
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distributions below do not separate tires by load rating, rather this descriptor is largely 

disregarded for CRR purposes. 

Tires with an identified application of “ultra light truck” or having “LT” in the model 

descriptor have also been included in this memorandum, though they have been analyzed 

separately from the other applications listed above. Light truck (LT) tires are most often fitted 

on heavy-duty pickup trucks and vans, though they also are used for light heavy-duty vocational 

vehicles. LT tires in the available data set include those with rim diameters from 16 to 19.5 

inches, and load ratings E, F, and G. Due to the different material properties of LT tires, the 

agencies adopted a provision in Phase 1 to allow manufacturers certifying vocational vehicles 

with LT tires to use a 0.87 adjustment factor before entering the tire CRR in GEM. The data 

presented below do not provide compelling information that a change to this adjustment factor is 

needed.

The distributions of tire CRR presented in this memorandum are based on a variety of 

source data. Data described below as “before Phase 1” means data obtained by testing conducted 

by Smithers Rapra and STL under contract with the EPA during development of the Phase 1 

rulemaking. Data described below as “since Phase 1” means data obtained by manufacturers 

between Feb 2012 and Dec 2013 and reported to NHTSA and EPA, as well as data obtained by 

testing conducted by Smithers Rapra under contract with NHTSA in 2011 and 2012.

For a variety of reasons, including questions about representativeness of the tire test data 

and unknown sales volumes, the agencies have not predicated the Phase 2 vocational vehicle 

standards on future market adoption rates that align with these tire CRR distributions, though the 

proposed standards are informed by these distributions. The purpose of presenting these data is 

to demonstrate that there is a wide range of CRR on tires that are commercially available for use 

on vocational vehicles.

Data Summaries

In Figure 1, the average CRR of the set of steer or all-position test tires intended for 

vocational vehicle applications is 6.67 kg/metric ton, which is about 13% better than the Phase 1 

vocational vehicle baseline tire CRR of 7.7. Of all the vocational steer tires for which we have 

test data, 275 (47%) of them were found to be at average CRR of 6.67 or higher (left side of 

graph), while 307 (53%) were found to have CRR lower than 6.67 (right side of graph). Of a 

total test sample of 582 tires, 13% of them were found to have CRR higher than 7.7, and 87% of 

them have CRR lower than 7.7 kg/metric ton. In terms of specific application types, steer and 

all-position tires intended for regional applications had an average CRR of 6.55 kg/ton. Steer and 

all-position tires intended for mixed service had an average CRR of 6.94 kg/ton. Steer and allposition tires intended for urban pickup and delivery applications had an average CRR of 6.77 

kg/ton.
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Figure 1: Number of Steer Tires Deviating from Average of 6.67 kg/metric ton

In Figure 2, the average CRR of the set of drive position test tires intended for vocational 

vehicle applications is 7.77 kg/metric ton, which is equal to the vocational vehicle baseline CRR 

(for both Phase 1 and Phase 2). Of all the vocational drive tires for which we have test data, 194 

(53%) of them were found to be at baseline CRR or higher (left side of graph), while 169 (47%) 

were found to be baseline or lower (right side of graph). Of a total test sample of 363 tires, 13% 

are 0 to 5% lower, 11% are 5 to 10% lower, 6% are 10 to 15% lower, 8% are 15 to 20% lower, 

and 8% have CRR more than 20% lower than the average. For this set of vocational drive tire 

data, there were no apparent patterns in terms of CRR for specific application types. The 

average CRR remained approximately 7.7 kg/ton whether looking at vocational drive tires 

specifically intended for regional, mixed service, or urban pickup and delivery applications. 

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20

40

60

80

100

120

Number of V

ocational Tires Tested

Percent Deviation from Average Vocational Steer/AP Tire CRR

Since Phase 1 All Before Phase 1
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Figure 2: Number of Drive Tires Deviating from Average of 7.77 kg/metric ton

Although the agencies do not have any information on the sales volumes of WBS tires for 

vocational vehicles, the data included tires intended for vehicle applications including mixed 

service, on/off highway, refuse, high scrub, special application, urban/mixed, and 

regional/mixed. In Figure 3, the average CRR of the set of wide-based single (WBS) test tires

with the above vehicle application identifiers is 6.56 kg/metric ton. This average is about 15 

percent better than the vocational vehicle baseline CRR of 7.7. Of a total test sample of 95 tires, 

11 (12%) of them were found to be at baseline CRR or higher, while 84 (88%) were found to be 

baseline or lower.

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10

20

30

40

50

60

70

Number of V

ocational Tires Tested

Percent Deviation from Average Vocational Drive Tire CRR

Since Phase 1 All Before Phase 1
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Figure 3: Number of Wide Base Single Tires Deviating from Average of 6.56 kg/metric ton

Although the agencies do not have information on sales volumes of light-truck (LT) tires 

that are installed on vocational vehicles, the data include some tires designated as LT that also

have intended vehicle applications such as Class 4 city delivery. In Figure 4, the average CRR 

of the set of LT test tires is 8.85 kg/metric ton, which is 15% higher than the vocational vehicle 

baseline CRR. Two-thirds of the LT test tires for which we have data are designated as allposition tires. The average CRR of those LT tires designated as steer tires is 8.33, and the 

average CRR of those LT tires designated as drive tires is 9.04 kg/metric ton. In Figure 4, the 

bars display the number of test tires that have CRR deviating from these respective averages by

different amounts. For example, there were 24 total tires with CRR between 10% and 15% 

higher than the average of 8.85, which would represent levels of CRR between 9.8 and 10.1 

kg/metric ton. The LT tire test data that have become available since Phase 1 include over 100 

all-position tires but only 13 drive tires and four steer tires. For these four steer tires, the average 

CRR was 7.8 kg/ton. For the 13 drive tires, the average CRR was 8.6 kg/ton. The newer data for 

all-position tires showed an average CRR of 8.9 kg/metric ton.

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2

4

6

8

10

12

14

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Number of V

ocational Tires Tested

Percent Deviation from Average Vocational WBS Tire CRR
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Figure 4: Number of Light Truck Tires Deviating from Average CRR of 8.85 kg/metric ton

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5

10

15

20

25

30

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Number of LT

Tires Tested

Percent Deviation from Average LT Tire CRR

Steer Drive All LT Tires