There are many factors to consider when choosing a set of wheels, or rims, for your ride. Factors such as style, finish, detailing and even weight can influence which wheel you decide on. However, the most important factor is choosing the right wheel fitment. Wheels need to be compatible with your vehicle and tire selection, regardless of style preferences. This guide will give you a general idea of what you should be aware of when purchasing a new set of wheels for your car while explaining wheel size.
Wheel Fitment Explained
The main dimensions of a wheel are the diameter, width, bolt pattern and offset. All of these individual dimensions come together to form the wheel size. Installing the right wheel for your specific vehicle will be based on these dimensions. But what exactly do each of these measurements mean?
For the sake of this guide, let’s work with an example wheel size of 18×9.5, 5×114.3 bolt pattern and an offset of +15.
Diameter
The wheel diameter in our example is 18”. The definition of wheel diameter is the distance, in inches, measured across the face of the wheel, from bead seat to bead seat. When measuring, take note that the meaurement should stop at the bead seat and not the full face of the wheel. Only wheels and tires of the same diameter can be safely mounted together; meaning you can only mount an 18” tire on an 18” wheel. The wheel diameter can also be found on the back side of the wheel, usually stamped behind one of the spokes. Wheel diameters vary, most commonly from 13” all the way up to 24”, sometimes even bigger for specialized low profile fitments.
Wheel Width
Wheel width is the distance, in inches, from bead seat to bead seat across the barrel of the wheel. The width of the wheel in this example is 9.5”. When measuring wheel width, be sure to stop at the bead seat and not at the full width of the wheel. The wheel width can have a direct impact on a tire’s contact patch if you decide to use a wider or narrower wheel option. By varying the width of the wheel, it will either enlarge or shrink your tire’s contact patch, leading to changes in your vehicle’s handling characteristics. Wheel widths can vary most commonly from 6” up to 14” wide, and in some unique cases, even wider.
Bolt Pattern
The bolt pattern, which is 5×114.3 in our example, is made up of two measurements. The first number, 5, indicates the number of lug holes the wheel has. The second number, 114.3, indicates the distance in millimeters from one hole to another, across the face of the wheel. It’s common for the second number in a bolt pattern to either be displayed in inches or millimeters, but most commonly millimeters. A wheel’s bolt pattern must exactly match the bolt pattern of the vehicle it is being mounted on. There are different types of bolt patterns, which you can learn about in our in-depth bolt pattern guide.
Offset
Wheel offset is the distance in millimeters from the mounting surface of the wheel and the wheel’s centerline. In our example, the wheel offset is positive 15mm; meaning the mounting surface is 15mm away from the centerline of the wheel. Having the right offset is essential to making sure the wheel fitment does not cause any rubbing issues with brakes, fenders or suspension components. The offset determines where the wheel and tire assembly sit in relation to the vehicle’s fender and suspension. There are three different types of offsets; positive, zero and negative. To learn more about wheel offsets, check out our in-depth wheel offset guide.
Wheel Fitment Recap
All of these wheel size measurements are critical in determining whether or not a particular set of wheels will fit. It’s also important to ensure that the wheel and tire combo are of a compatible width and diameter.
Have questions regarding wheel sizing or having fitment issues? Feel free to get in touch with us and our wheel experts would be happy to assist you!