The wheel rim is placed in compression by the tension in the spokes of a conventional wheel. To make this a light-strong structure and reduce the rotational kinetic energy and inertia of the wheels, the rim is frequently fabricated from a light alloy extrusion. This construction also provides rim surfaces on which the brake friction material can act.

The rim holds the tire and tube. A lip on the inside of the outer edge of the rim provides a seat for the tire bead and stabilizes the tire against blow-off. The inner-tube retains the compressed air that acts as a 'suspension' medium for the outer tire. Adjustment of the tire pressure influences the road shock adsorption capability of the tire and its rolling resistance.

The tire tread is selected to minimize the rolling resistance on a particular surface type and provide the tire/ground friction forces required for maneuver.

From: Apps, "The Bicycle Book," Smithmark (1993)