Alloy wheel dimensions and fitment explained
A guide on what dimensions and information to look for when buying aftermarket alloy wheels for your astra....
The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.
The hub mounting surface is even with the centerline of the wheel.
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.
If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly.
The centerbore of a wheel is the size of the machined hole on the back of the wheel that centers the wheel properly on the hub of the car. This hole is machined to exactly match the hub so the wheels are precisely positioned, minimizing the chance of a vibration. With a hubcentric wheel, the lug hardware will not be supporting the weight of the vehicle, all they really do is press the wheel against the hub of the car. Some wheels use high quality, forged centering rings that lock into place in the back of the wheel. This is an acceptable alternative.
If you have non-hubcentric (lugcentric) wheels, they should be torqued correctly while the vehicle is still off of the ground so they center properly. The weight of the vehicle can push the wheel off-center slightly while you're tightening them down if left on the ground.
The bolt pattern or bolt circle is the diameter of an imaginary circle formed by the centers of the wheel lugs. Bolt patterns can be 4, 5, 6, or 8 lug holes. A bolt circle of 4x100 would indicate a 4 lug pattern on a circle with a diameter of 100mm.
The diagram indicates the proper measuring methods. 6 lug wheels are measured like the 4 lug wheels.
Conversion TableInchesMillimeters4 x 3.934 x 1004 x 4.254 x 107.954 x 4.334 x 1104 x 4.504 x 114.34 x 5.124 x 1304 x 5.514 x 1405 x 4.005 x 1005 x 4.255 x 107.955 x 4.505 x 114.35 x 4.535 x 1155 x 4.725 x 1205 x 4.755 x 120.655 x 5.125 x 130
While many aftermarket alloy wheels are designed to use your car's original lug nuts or bolts, others require new hardware. It may be something as critical as differences in the wheel's lug seat design as shown below, or something as simple as shorter lug heads to allow the wheel's center caps to fit. If your new wheels require new hardware, your invoice will list the appropriate quantity identified by our part description, beginning with an "N" for lug nuts or a "B" for lug bolts followed by the size, pitch, seat design, length and the appropriate lug wrench socket size.
NOTE: Keep a set of your vehicle’s Original Equipment lug nuts or bolts in the trunk just in case you ever need to use your factory spare tire, which must always be installed with the Original Equipment lug hardware.
Plus sizing your wheels and tires is the best way to improve both the performance and appearance of your vehicle. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall diameter of the tire, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious, most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks.