A front road bike wheel with a carbon fibre rim, aluminium hub and steel spokes. Carbon composite has a number of advantages as a material for bicycle wheel rims. It is stronger, stiffer and lighter gram-for-gram than aluminium and as a result has encouraged more aerodynamic design. The deep ‘aero’ rim of this example reduces wind drag by 10 % as compared with standard rims but would be too heavy if made of aluminium. Weight as well as shape is a factor: a lighter wheel is a faster wheel because it accelerates more quickly. The nature of carbon fibre and, as a result, how it is worked also contributes to its effectiveness. It consists of long carbon fibres of great directional strength and stiffness that are held together in resin. The alignment and weave of the fibres is chosen to optimize the strength and stiffness required. To make the rim, fibres are laid around a mould in the shape of the finished rim. The mould is then filled with resin and cured to a high temperature. The emerging form is a clean aerodynamic profile that is unattainable with metal working processes. Carbon fibre wheels tend to cost twice as much as their aluminium alloy counterparts.