THE USE OF A PORTABLE POWER METER TO ESTIMATE AERODYNAMIC AND ROLLING RESISTANCE IN ROAD CYCLING

Abstract

PURPOSE To develop a protocol for isolating aerodynamic resistance (Ra) and rolling resistance (Rr) from field based measures of power (watts) and velocity (V in m/s-1) during level cycling. METHODS We assessed the effect of body position (Brake Hoods vs. Drops) and tire pressure changes (60 psi vs. 120 psi) on Ra and Rr by measuring the power vs. speed relationship using commercially available power meters (PM). Bi-directional measurements were taken while subjects cycled on their personal road racing bicycle equipped with a PM in wind free (wind velocity < 1.0 m/s-1) conditions at a constant velocity (acceleration < 0.5 m?s-2) on a flat 0.2 km section of a smooth asphalt road from 100 to 300 W for women (n = 2) or 100 to 400 W for men (n = 6) in 50 W increments. Ra was calculated as the slope of the linear relationship between tractive resistance (y, RT = force in Newton or joule?m-1) and velocity squared (x, m2/s2), while Rr was calculated as the intercept of this relationship. RESULTS (Mean ± SD): Ra was significantly greater in the brake hoods compared to the drops at both 60 psi (0.1765 ± 0.0290 vs. 0.1574 ± 0.0280) and 120 psi (0.1744 ± 0.0289 vs. 0.1544 ± 0.0268 N?V-2) with no effect attributable to tire pressure. Rc was significantly greater at 60 psi compared to 120 psi in both the brake hoods (5.6736 ± 0.7825 vs 4.2858 ± 0.854) and drops (5.4761 ± 0.6119 vs. 4.1444 ± 0.7769 N) with no effect attributable to body position. CONCLUSIONS A change in body position significantly changed aerodynamic resistance but not rolling resistance while a change in tire pressure significantly changed rolling resistance but not aerodynamic resistance. These results demonstrate that commercially available power meters are sensitive enough to detect changes in aerodynamic and rolling resistance due to changes in body position and tire pressure. This work supported by Cycleops Power Tap