Alloy wheels are automobile (car, motorcycle an truck) wheels which are made from an alloy of aluminum or magnesium metals (or sometimes a mixture of both). Alloy wheels differ from normal steel wheels because of their lighter weight, which improves the steering and the speed of the car, however some alloy wheels are heavier than the equivalent size steel wheel. Alloy wheels are also better heat conductors than steel wheels, improving heat dissipation from the brakes, which reduces the chance of brake failure in more demanding driving conditions. Alloy wheels are more expensive to produce than standard steel wheels, and thus are not included as standard equipment on many vehicles, instead being marketed as optional add-ons or possibly included as standard equipment on higher-priced "luxury" or "sport" models. Alloy wheels are prone to Galvanic corrosion if appropriate preventive measures are not taken.