Energy cost and efficiency of riding aerodynamic bicycles

Summary

Traction resistance (R _t) was determined by towing two cyclists in fully dropped posture on bicycles with an aerodynamic frame with lenticular wheels (AL), an aerodynamic frame with traditional wheels (AT), or a traditional frame with lenticular wheels (TL) in calm air on a flat wooden track at constant speed (8.6–14.6 m·s⁻¹). Under all experimental conditions, R _t increased linearly with the square of air velocity (ν_a ²); r ² equal to greater than 0.89. The constant k = ΔR _t/Δν_a ² was about 15% lower for AL and AT (0.157 and 0.155 N·²·m⁻²) than for TL bicycles (0.184 N·²·⁻²). These data show firstly, that in terms of mechanical energy savings, the role of lenticular wheels is negligible and, secondly, that for TL bicycles, the value of k was essentially equal to that found by others for bicycles with a traditional frame and traditional wheels (TT). The energy cost of cycling per unit distance (C _c, J·m⁻¹) was also measured for AT and TT bicycles from the ratio of the O₂ consumption above resting to speed, in the speed range from 4.7 to 11.1 m·s⁻¹. The C _c also increased linearly with ν_a ², as described by: C _c = 30.8 + 0.558 ν_a ² and C _c = 29.6 + 0.606 ν_a ² for AT and TT bicycles. Thus from our study it would seem that AT bicycles are only about 5% more economical than TT at 12.5 m·s⁻ the economy tending to increase slightly with the speed. Assuming a rolling coefficient equal to that observed by others in similar conditions, the mechanical efficiency was about 10% lower for aerodynamic than for conventional bicycles, amounting to about 22% and 25% at a speed of 12.5 m·s⁻¹. From these data it was possible to calculate that the performance improvement when riding aerodynamic bicycles, all other things being equal, ought to be about 3%. This compares favourably with the increase of about 4% observed in world record speeds (over distances from 1 to 20 km) after the adoption of the new bicycles.