Wheels can be factory made or custom built. Factory wheels come on every stock vehicle but they may not be the right wheel for the car's owner. As new, custom look, an upgraded tire and wheel package that compliment the owner's vision of great automotive styling works great. Getting the right wheel for a vehicle equals buying one that fits and looks great. Every wheel has specific measurements that make it right or wrong for the vehicle. Always measure new car wheels to know which ones you are buying.
Lay the wheel flat on the ground with the inboard flange facing up. The inbound flange is the rim of the wheel that will be facing in, toward the body of the car, when it is installed. In order to get one of the measurements of a wheel to know if it is the right one for a particular vehicle, the backspacing must be determined. This is measured from the inbound flange down to the hub centre that is centred onto the axle. Use a straight board to lay across the width of the wheel on the inbound flange and measure with a ruler down to the centre hub. This is the wheel's backspacing.
Measure the lug pattern of the axle that the wheel will be mounted to. Lug Centric wheels are centred on the axle by the lugs that protrude from the axle and that the wheel is secured with. Lugs come in patterns of 4, 5, 6, or 8 lugs depending on the vehicle. For the even numbered lug patterns you measure from centerline of one lug hole to the centerline of the lug hole that is opposite from the one being measured. On odd numbered lug patterns, the lug holes measured from the top of the top lug hole to the centerline of the lug hole two away from the starting hole. This will be the measurements that let you buy the right lug pattern for a replacement wheel.
Measure the centerline of the wheel to determine if the replacement wheel has, or will need, a positive or negative offset. This offset is determined by the placement of the centre hub in relation to the centerline. To find the centre line you must measure from the inboard flange of the wheel to the outboard flange of the wheel and divide by two. Measure with a ruler or tape measure from the inside lips of the inbound and outbound flanges to get the right centerline measurement. Then do the division.
The offset of the wheel will be the backspace of the wheel in comparison to the centerline. An example would be if a wheel's backspace was 6 ¾ inches and the wheel centerline was 8 inches. This would mean that the wheel has a negative offset. If the wheel's backspace was 6 ¾ inches and the centerline was 6 inches, the offset would be positive. Having the right wheel offset allows for the tire to spin freely within the space provided by the vehicles axle, body panels and frame. The wrong offset could mean that the wheel may rub on the inside of the wheel well, the outside of the wheel well, or even the brake caliper or rotor may come in contact with a wheel that is not compatible with the vehicle. Any of the wheel measurements that are wrong can cause the wheel to perform poorly, or not at all.
Measure the stock wheel to determine the size of a wheel that has already been installed on the vehicle. These wheels have the important information you need to buy a replacement. To alter the backspace or width of a wheel it will be necessary to determine the space provided by the vehicle for instalment, the performance that is needed during operation and how the caliper will fit inside the wheel once installed. The existing wheel will show you what measurements work, and then you can alter from a stock setting accordingly.
Select a tire before the wheel. Knowing the tire size will help fit a wheel to match both tire and vehicle equally.
The wrong offset can cause axles and lugs to break because of the point of weight distribution the new offset puts on these moving parts. Avoid damage to lugs, brake calipers and axles by maintaining an offset that works within the vehicle's specifications.