Buying Guide

How TO READ A WHEEL SPEC SHEET. What very spec actually means for your car.

Buying new wheels should be simple, until you’re faced with a string of numbers like 18x8.5J, 5x112, ET35, 66.6mm.

Those numbers aren’t just technical details. They determine whether a wheel will bolt onto your car, sit correctly in the arch, clear the brakes, and work safely with the rest of your setup.

In this guide, we’ll decode the key parts of a wheel spec sheet, including PCD, offset, centre bore, width and diameter. We’ll explain what each measurement means, why it matters, and what can happen when you get it wrong.

By the end, you’ll be able to look at a wheel specification and know exactly what it means for your car.

Fitment

Frustratingly there is no universal fitment for wheels and there are several technical factors that have to be considered when selecting new wheels for your vehicle. However, the good news is that we’ve got you covered. The Wheel Guys’ wheel selector has our expertise built-in. Simply enter your vehicle’s details and we’ll do the rest for you. No need to find the manual; no complicated VIN lookups. Our website does all the thinking, so you don’t have to. Want to understand fitment for yourself? Read on. There are 50+ fitment variations to get your head around. There are a few basic dimensions that affect the fit, the appearance and what tyres you’ll need.

PCD

PCD stands for 'pitch circle diameter' and is basically the measurement between the bolt holes. It is vital that the alloys have the same PCD as the vehicle's wheel hub.

Wheel Diameter

Wheel Diameter is the measurement across the face of the wheel, not including the wheel lips (the part of the wheel that helps keep the tyre in place)

Wheel Width

Wheel Width is the measurement from the inside of the wheel lip, across the wheel to the other lip.

Bolt Pattern Styles & Dimensions

There are four common bolt pattern styles:

4, 5, 6 & 8 lug and each can be found with several different bolt circle dimensions.

To determine the bolt pattern dimensions for your wheel you need to measure. If you have a 4, 6 or 8 wheel lug, measure from 2 holes directly across from one another.

5 lug wheels are measured from the back of 1 hole, to the centre of the opposite 2 holes.

4 x 100

The number 4 refers to the number of holes in the wheel. The number 100 refers to the diameter of the circle of boltholes measured in millimetres.

Wheel Offset

Wheel Offset is the dimension from the rear of the mounting face to the centre line of the wheel.

Wheel Back Spacing

Wheel Back Spacing is the measurement from the rear of the mounting face to the back side wheel lip

Wheel Offset

Both the wheel offset and the wheel backspacing affect your vehicle’s suspension and brake clearance. There are 3 different types of wheel offset:

Positive
Zero
Negative offset.

Remember that the offset is measured from the inside of the wheel’s mounting face to the true centreline of the wheel.

A positive offset wheels hub mounting surface will be shallow, closer to the street side.

A negative offset wheel will be deeper, or have a mounting face that’s closer to the back side of the wheel, than the front side.