LEARN THE LINGO
PCD: Pitch Circle Diameter is the diameter of an imaginary circle that passes through the centre of the wheel’s mounting bolts. It’s related to the number of and spacing between wheel studs on your car. It’s the first critical stat, as it tells you whether the wheels will even bolt up to your car.
OFFSET: The distance from the hub’s mounting surface and the wheel’s centre line, which is the middle point between the rims. It measures where the tyre sits laterally from the hub of the wheel. Deep-dish wheels have a negative offset. Many late-model stock wheels, where the face is almost flush with the outer edge of the lip, have a positive offset.
BACKSPACE: The distance from the rear of the wheel mounting pad to the edge of the inside lip of the wheel. Deep-dish wheels have a small backspace number; conversely, wheels with minimal dish have a large backspace number.
CENTRE BORE: Also called the spigot, the centre bore is the machined hole in the back of the wheel. It is machined to match the hub for a snug fit. This set-up is known as hub-centric, and ensures the wheel runs true to minimise vibration, and that wheel studs and nuts are not supporting the weight of the vehicle (their job is to hold the wheel against the hub).
RIM: Sometimes used as a slang term for the wheels themselves, the rim is actually the top outer edge of the wheel. The inside edge of the rim is where the tyre is mounted, making it a critical part of the wheel. Wheel diameter is measured across the barrel, not from rim to rim. LIP: The outer face of the wheel, including the outer rim, which is joined to a barrel and centre. These are offered in several styles, including a step-lip or slant-lip, which use a larger vertical flange to convert a small-diameter threepiece wheel centre into a largerdiameter wheel.