Document ID: EPA-HQ-OAR-2014-0827-0116
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-07-13T04:00Z

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 Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827

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

 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. 

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 all-position 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. 

Figure 4:  Number of Light Truck Tires Deviating from Average CRR of 8.85 kg/metric ton