There are various types of lightweight and aerodynamic wheels available for triathlon bicycles. Some wheels have an aerodynamic ring, flat spokes or fewer spokes than the traditional 32 spokes. Others have carbon-fiber tri-spokes, which are three large, stiff spokes. Solid wheel discs are also used, but mainly on the back wheel because front wheel discs are hard to handle in crosswinds. Some bikes use wheels with a nominal diameter of 65 centimeters instead of the traditional 70 cm wheels used on most road bikes. Smaller wheels are lighter and have a smaller cross-sectional area, which in effect reduces wind resistance of the wheel and the bike because the frame and cyclist are closer to the ground. However, a smaller wheel means higher curvature at the tire's surface, which increases rolling resistance or friction with the ground.
