Until recently, the wheels fitted by most manufacturers to their everyday cars have been "steel wheels" Steel wheels are more resilient to damage, and are considerably cheaper to fit. Unfortunately they are heavier, less attractive and smaller in both diameter and width than alloy wheels. The term alloy wheels is usually given to wheels 'cast' from a mixture of aluminum which is lightweight and great at dissipating heat and small amounts of more rigid metals whose presence in the 'mix' provides rigidity and helps prevent crack propagation