Vehicle Bolt Patterns and Wheel Fitment
When attempting to understand wheel fitment and tire sizing, there are a few fundamentals that are essential to your understanding and can facilitate the process to comprehension. The first of these fundamentals are bolt pattern. The bolt pattern assists in determining the number of mounting holes for the bolts as well as the position of the holes.
Why is this pattern important?
Good question! This pattern determines where the bolts will go that are responsible for bolting the wheel to the hub for the vehicle.
An important measurement when studying wheel fitment, and how it pertains to any specific vehicle, is the PCD. Standing for ‘Pitch Circle Diameter,’ the PCD measures the distance from two bolts that sit opposite each other in the bolt circle. The bolt circle is the imaginary shape that is created by the position of the bolts. Depending on the make and model of the vehicle’s corresponding wheels and tires, the bolt circle may be made up of any number of bolts. However, the more common positioning contains 4 or 5 bolts. When constructing the bolt circle that contains an even number of bolts, you simply measure the distance between two oppositely positioned bolts in the circle to get the PCD. Understandably so, coming up with this same measurement for a bolt circle that contains an uneven number of bolts is a tad more challenging. A little imagination must be involved to measure the distance from two oppositely positioned points (not necessarily bolts) in the bolt circle.
Once this measurement is taken, it is recorded and shown as a measure of bolts over the diameter, or distance, itself in millimeters. In other words, you may see a PCD measurement written as 5/120. The technical translation of this is a bolt circle that consists of 5 bolts and has a measured diameter of 120 mm.
The pitch circle diameter plays an important role in wheel sizing. Obtaining the measurement for both the hub and the wheel will allow you to easily match and fit the correct sizes to each other so that you have an aligned and precisely matched construction. This measurement is also helpful at determining whether a wheel or hub that are not perfectly matched can be fit together by the use of variance bolts. In any case, knowing how to measure the pitch circle diameter will act as a useful tool in fitting together a wheel and hub during the process of tire sizing.