Review of the 21st Century Truck Partnership, Second Report (2012)
Chapter: Appendix G: History of Heavy-Duty Truck Aerodynamic and Tire Rolling Resistance Coefficients
History of Heavy-Duty Truck Aerodynamic
and Tire Rolling Resistance Coefficients
The most recent 21st Century Truck Partnership (21CTP) white paper1 adopted the Environmental Protection Agency’s (EPA’s) Cd and Crr baselines from the proposed EPA/National Highway Traffic Safety Administration (NHTSA) greenhouse gas (GHG) rule that were to represent roughly the median of current in-use equipment for highway duty tractor-trailers with high-roof sleepers (identified in Table G-1) as “EPA GHG Rule Conventional High-Roof Average T-T.” These coefficients are higher than those used in previous Partnership documents and prevailing industry documents, which represented circa 2005 to 2009 production available designs and components, identified in Table G-1 as “NRC 21CTP Review, Phase 2.” See also footnote e in Table G-1 .
Notice for example, that the currently available EPA SmartWay aerodynamics and tires (0.59 and 0.0063) provide lower fuel consumption than is achievable with the Average T-T base coefficients in the EPA/NHTSA GHG rule (0.69 and supposed combination weighted 0.0077), by about 7 percent and 6 percent, respectively; 13 percent when combined.
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1Received by the committee on March 17, 2011.
TABLE G-1 History of Heavy-Duty Truck Aerodynamic and Tire Rolling Resistance Coefficients
| Truck Configuration Description | Cd | Crr | |||
| Steer | Drive | Trailer | Weighted Averagea | ||
| 1974 COE T-Tb | 1.02 | 0.0103c | |||
| 1974 COE T-T, Closed Gap, Trailer Skirts, Boat-Tailb | 0.46 | ||||
| EPA Classic Conventional, Exterior Air Cleaners, Verticle Exhaust, Flat Bumber, No Aero Features T-T | 0.77 | ||||
| EPA GHG Rule (CE-CERT) 2000’s Conventional High Roof T-T | 0.74 | ||||
| EPA GHG Rule Conventional High-Roof Average T-T | 0.69 | 0.0078 | 0.0082 | 0.0072d | 0.0077 |
| NRC 21CTP, Phase 2, Mid-2000s Conventional High Roof, pre-S/W T-Te | 0.63 | 0.0068 | |||
| EPA GHG Rule Conventional High-Roof SmartWay T-T | 0.59 | 0.0059 | 0.0074 | 0.0053 | 0.0063 |
| EPA GHG Rule Conventional High-Roof Advanced SmartWay T-T | 0.55 | 0.0055 | |||
| NRC 21CTP Review, Phase 2, Conventional High Roof, 2015-2020 T-T | 0.45 | 0.0045 | |||
NOTE: COE T-T: Cab Over Engine Tractor-Trailer. T-T: Tractor-Trailer. The Cds’ and the Crrs’ in the table are not derived from a consistent set of measurement or test procedures.
a Weightings: Steer (12), Drive (34), Trailer (34) reflect distribution of (80,000) lb Gross Vehicle Weight (GVW).
b K.R. Cooper, Commercial Vehicle Aerodynamic Drag Reduction: Historical Perspective as a Guide, The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, October 15, 2004. Springer.
c Based on bias ply tires.
d Assumed by National Research Council committee.
e Reducing Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions, NESCCAF/ICCT, Miller ed., October, 2009; and Cd same as the DOE 2006 21st Century Truck Roadmap and Technical White Papers. Doc No. 21CTP-003, December, Washington, D.C.
