ENERGY-COST AND EFFICIENCY OF RIDING AERODYNAMIC BICYCLES

Traction resistance (Rt) was determined by towing two cyclists in full y dropped posture on bicycles with an aerodynamic frame with lenticula r wheels (AL), an aerodynamic frame with traditional wheels (AT), or a traditional frame with lenticular wheels (TL) in calm air on a flat w ooden track at constant speed (8.6-14.6 m . s-1). Under all experiment al 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 whe els is negligible and, secondly, that for TL bicycles, the value of k was essentially equal to that found by others for bicycles with a trad itional 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 bicy cles from the ratio of the O2 consumption above resting to speed, in t he speed range from 4.7 to 11.1 m . s-1. The C(c) also increased linea rly 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 woul d seem that AT bicycles are only about 5% more economical than TT at 1 2.5 m . s-1 the economy tending to increase slightly with the speed. A ssuming a rolling coefficient equal to that observed by others in simi lar conditions, the mechanical efficiency was about 10% lower for aero dynamic 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 calcul ate that the performance improvement when riding aerodynamic bicycles, all other things being equal, ought to be about 3%. This compares fav ourably with the increase of about 4% observed in world record speeds (over distances from 1 to 20 km) after the adoption of the new bicycle s.