Wheels must be strong enough to support the vehicle, and withstand the forces caused by normal operation. At the same time, they must be as light as possible, to help keep unsprung weight to a minimum.
Wheels can be made from pressed steel, in 2 sections - the flange or disc that is drilled for the wheel fasteners, and the rim.
Wheels can also be made from cast aluminum alloy. Alloy wheels are popular because of their appearance and because they are lighter than similar steel wheels. Aluminum is a better conductor of heat, so alloy wheels can dissipate heat from brakes and tires more effectively than steel ones. These are often called mag or magnesium wheels, but wheels made of magnesium are rarely used on road vehicles.
Most wheels have ventilation holes in the flange, so air can circulate to the brakes.
Most passenger car wheels are of well, or drop-centre design. This design allows for tire removal and fitting.
Tires for heavy goods vehicles are much stiffer but they can also be fitted to a well-based rim or to a flat-base detachable flange rim, depending on construction.
