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- 1975 June 2 1 , 2011 **Proposed GHG/FE Rule Aerodynamic**  **Certification Issues** 
**I. Reference Method**  A. An aerodynamic drag “reference method” should be u sed to correlate manufacturers’ individual methods. M anufacturers would test vehicles using the reference method and compare the Cd results to the results from th eir own metho d s . B. Coastdown appears to be an acceptable “reference method” for the near term. However, the results from coastdown testing of heavy- duty v ehicles are significantl y affected by wind conditions , track conditions, and tire rolling resistance. The existing SAE Recommended Practices for coastdown testing ( i.e., J1263 and J2263) do not sufficiently address those issues for heavy
- duty vehicles. Accordingl y, EMA/TMA is supporting SAE in developing a new procedure for heavy- duty vehicles. In the meantime, there must be allowances in the rule to minimize and/or account for those inf luences
. The following enhancements are warranted to the coastdown procedures proposed in Part 1066 , Subpart C: 1. Average and cross wind speeds ≤2 .0 mph. Even wind conditions within the specifications of section 7.3 of SAE J1263 ( i.e., average speeds no more than 10 mph (or peaks no more than 12.3 mph) and cross winds no more than 5.0 mph) may

significantl y influence the measured Cd
. 2. No anemometer may be mounted to the tractor; relative wind speed should be measured with one or more track
- mounted anemometers . I f an anemometer is mounted to the vehicle, it must be mounted to the trailer to avoid affecting air flow around the tractor. 3. Test track or road must be dry, clean, straight, smooth, hard
- surfaced, not have excessive crown, and have a consistent grade of no more than 0.02%. For surfaces that are not level, the force contribution due to gravity must be determined per section 11.5 of SAE J2263. 4. Tractor tires a. Size: 295/75R22.5 or 275/80R22.5 b. C RR ≤ 6.0 kg/metric ton c. Broken in per section 8.1 of SAE J1263 d. Pressure per section 8.5 of SAE J1263 e. No uneven wear f. No re
- treads 5. To achieve consistent results, the assumptions used in the aerodyn amic drag calculations should be standardized ( e.g., using specified software).2 6. Test from 70 mph 7. Unloaded “ standard trailer” 8. Drivetrain rotational inertia = 125 lbs. per tire 9. Data is acceptable if within two standard deviations of the average of runs in the same direction. C. The “reference method” should be used to make adjustments to the Cd bin values proposed in § 1037.510. Those adjustment s include overall bin Cd values and day cab values relative to sleeper cab value s. 1. Based on six comparisons, day c abs are 2.5% to 13.1% worse than the same model in a sleeper configuration. The average is 8.5% worse. 2. Cd values for day cab bins should be 8.5% higher than for sleeper cabs. D. Data is needed for analysis of the proposed coastdown procedure and readjustment of bins as appropriate. **II. Correlation**  **Factor** A. Each manufacturer tests a high
- roof “golden tractor” using the “reference method” and establish a “correlation factor” (or, “CF”) for each of their own methods. For example, the “correlation factor” for a manufacturer’s CFD anal ys is is : C F CFD = Cdref method golden tractor / CdCFD golden tractor B. The manufacturer calculate s the Cd for determining the applicable bin category for a particular tractor (per § 1037.520(b)(2)) using the results of the manufacturer’s CFD analysis times the “ CFD correlation factor” as follows: Cd bin = CdCFD * CF CFD **III. Standard Trailer**  A. To ensure that all certification is done with trailers that are identical in all aspects that affect aerodyn amics, EPA should revise the definition of “standard high
- roof trailer” proposed in § 1037.501(g) as follows: 1. Gap (back of cab to front of trailer): 44 " ±2.0 "
. If onl y a smaller gap is achievable, use the largest gap achievable. 2. Overall height (from top of trailer to ground on landing gear, in level condition): 13 ' 6 " +0.0 "
- 1.0 " 3. Front height (from top of trailer to fifth wheel plate): 115" ±1 .0" 4. Length: 53' ±1 .0 " 5. Width: 102 " ± 0.5 :" 6. Front corners: 5.5 " radius ± 0.5 " 7. King pin (from front of trailer to king pin center line): 36" ± .5"3 8. Landing gear (front of trailer to centerline of landing gear): 105 " ±4.0 " 9. Rear axles (axle centerline to rear of trailer): 14 6 " ± 3 .0" 10. Underride guard per 49 C.F.R. § 393.86 11. Tires a. Size : 295/75R22.5 or 275/80R22.5 b. C RR<5.1 kg/metric ton (In addition, the C RR for trailer tires in GEM should be updated to 5.0 kg/metric ton.) c. Broken in per section 8.1 of SAE J1263 d. Pressure per section 8.5 of SAE J1263 e. No uneven wear f. No re
- treads B. The rule should not include “standard trailers” for low
- and mid
- roof tractors. **IV. Wind Average**  **d Drag**  A. The rule should recognize wind
- average d aerody namic drag performance. B. Allow manufacturers to adjust emissions levels based on a vehicle’s wind
average d drag performance compared to an industry baseline” 1. Use a ± 6 ° yaw to establish an industry baseline 6 ° /0 ° Cd ratio a. Preliminary

industry results indicate a baseline ratio of 1. 20 b. Additional data made be needed 2. Using GEM, establish the emissions of the subject tractor using its Cd times the industry

baseline ratio. 3. Establish the emissions of the subject vehicle using its ± 6 ° yaw Cd. 4. Use the ratio of the two emissions level s above to adjust its regular emissions ( i.e., its GEM output using 0 ° yaw Cd) **V. Low**  **- and Mid**  **- Roof Tractors**  A. Due to unpredictable air flow, lower VMT, lower sales volumes, and more weight sensitive and more on/off road application s , manufacturers place a lower priority on low
- and mid
- roof tractor aerody namics than they

do on high
- roof tractors. 1. To simplify

c ertification of low
- and mid
- roof tractors, a manufacturer should be allowed to “carry
- over” the performance of the high
- roof version of the same model. Tractors would be considered the same model as long a s the tractors have the same bumper, hood, cab and sleeper ( i f applicable). 2. There should be onl y two bins for low
- and mid
- roof tractors : “ C lassic” and “ Smartway
. ” If the high
- roof version of a model is Conventional, Smartway, Advanced Smartway, or Advanced Smartway II, the low
- and mid
- roof versions would be in the “ Smartway” bin
. If the high
- roof version of a model is Classic, the low
- and mid
- roof versions would be in the “ C lassic ” bin
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B. Alternativel y, a manufacturer may measure and establish a Cd in the same manner as high
- roof tractors to determine if the low
- or mid
- roof tractor would fall in the “ C lassic ” bin or the “ Smartway” bin
. To do so , the manufacturer would test or anal yz e the tractor in its bobtail configuration. **VI. Enforcement**  A. If one of the Agencies au dits a manufacturer ’ s Cd determination, they may a ssign a new bin and require that the manufacturer make up any credit deficit and change the bin category

of the tractor for the next model year. 1. The Agencies m ay test using either the “reference method” or the manufacturer’s method. 2. If the average or cross winds exceed 2.0 mph, the results must be corrected to account for wind influences. 3. Manufacturers should be afforded a +/
- one bin “compliance margin” ( i. e., a tractor would have to be off b y more th an one bin)
. B. If one of the Agencies determines that the tractor must be moved to different bin, only “identical” tractors would be affected. “Identical” tractors must be the same in all aspects that affect aerodynamics. **VII. Aerodynamic Descriptions**  A. The rule should not include the requirement in § 1037.520(b)(4) for a manufacturer to obtain approval from EPA to move a tractor to a higher bin than its bin determined by the vehicle design characteristics
. B. The rule should not include § 1037.141. **VIII. Frontal Area**  A. The rule should use the tractor’s actual frontal area for determining Cd. B. The ranges in Table 2 in § 1037.520 should be specified in CdA. **IX. Drag Coefficient Equation**  A. Revise the proposed equation in § 1037.5 20(b)(i)(A) to read as follows:

C DA = D/(1/2) ρ B. ρ = actual air density (so that D does not need to be corrected)

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