ENERGY-COST AND EFFICIENCY OF RIDING AERODYNAMIC BICYCLES

Traction resistance (Rt) 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, increased linearly with the square of air velocity (v(a)2); r2 equal to greater than 0.89. The constant k=DELTAR(t)/DELTAv(a)2 was about 15% lower for AL and AT (0.157 and 0.155 N . S2 . M-2) than for TL bicycles (0. 1 84 N . S2 . m-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 v(a)2, as described by: C(c) = 30.8 + 0.558 v(a)2 and C(c) = 29.6 + 0.606 v(a)2 for AT and Tr bicycles. Thus from our study it would seem that AT bicycles are only about 5% more economical than TT at 12.5 m . s-1 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.