Results of Energy-Loss Measurements on Passenger Car Tires Operating in the Free-Rolling and Braking/Traction Modes

Bogdan, L. · 1980 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This report presents the results of energy-loss measurements conducted on twelve passenger car tires to evaluate performance under varying operational conditions. Sponsored by the U.S. Department of Transportation’s National Highway Traffic Safety Administration, the study aimed to quantify tire energy loss in free-rolling states versus dynamic braking and traction modes. The motivation was to determine if tire rankings for energy efficiency remain consistent across different test cycles, specifically comparing steady-state conditions with the Federal Urban Driving Cycle (LA-4) and the Federal Highway Fuel Economy Test (HFET). The experiments were performed at Calspan’s Tire Research Facility (TIRF) using a representative sample of original equipment tires ranging in size from P155/80D13 to HR78-15. Each tire underwent three types of tests: steady-state free-rolling at 50 mph with loads equal to 80% of the rated load; LA-4 cycle simulation (1,370 seconds); and HFET cycle simulation (765 seconds). For the dynamic cycles, wheel torques were calculated based on a simulated vehicle weight equal to twice the tire’s normal load, accounting for inertial forces during acceleration and deceleration. Data acquisition utilized specific sampling rates—every four seconds for steady-state, every 2.2 seconds for LA-4, and every two seconds for HFET—to accommodate computer storage limits while maintaining resolution. All tires underwent a General Motors break-in procedure prior to testing. The findings indicate that energy loss values generally follow a specific hierarchy: steady-state free-rolling conditions yielded the lowest losses, followed by HFET cycle conditions, with LA-4 cycle conditions producing the highest energy losses. Crucially, the relative ranking of the tires remained largely consistent across all three test conditions, suggesting that a tire’s efficiency profile is stable regardless of the operational mode. However, the study identified significant sensitivity in measured energy loss to the transient response characteristics of the torque servo system. Tests revealed that an underdamped servo response could artificially inflate energy loss measurements due to oscillatory torque inputs, although this did not alter the relative ranking of the tires. The significance of this work lies in its validation that steady-state testing can reliably predict relative tire performance in dynamic driving cycles, simplifying evaluation protocols. However, the authors caution that absolute energy loss values in cycle tests are highly dependent on servo control fidelity. They recommend future testing include aerodynamic drag and rolling resistance of other vehicle components in torque calculations and suggest transitioning from wheel-torque servoing to longitudinal force servoing to improve measurement accuracy and stability.

Key finding

Relative energy-loss rankings among passenger car tires remained relatively independent of the test cycle, although measured energy loss values under traction conditions were significantly higher than steady-state values and highly sensitive to torque servo transient response.

Methodology

lab_experiment

Sample size: 12

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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