Looking at new rims and noticing a number called wheel offset? It may seem like just another number, but it plays an important role in wheel fitment. Simply put, it shows where the wheel sits once fitted to the hub. While setting the wheel’s position on the hub, it also affects the clearance around the suspension and the tyre’s position inside the guard. However, excessive changes in wheel offset can cause clearance issues around the suspension or guards.
To make things easier for you, we created this guide to break it down and explain how you can measure it on your wheels.
What Exactly is Wheel Offset?
As mentioned earlier, wheel offset affects how a wheel sits on your vehicle. This is the measurement that shows the distance between the wheel’s centreline and the mounting surface. Across the middle of the wheel runs the centreline, which divides it into two equal halves. On the back of the wheel sits the mounting surface, the flat area that attaches to the hub. Because of its position, the mounting surface determines how far the wheel can sit inside the guard. Aside from that, it also influences how much the wheel can extend outward from the vehicle.
Often, drivers notice this when comparing factory wheels to aftermarket rims. For instance, two wheels may appear identical in diameter and width. But once they are fitted, they may sit differently because of the offset measurement. As such, manufacturers carefully select wheel offset. The goal is to keep the wheels aligned with the suspension and steering setup at all times.
Wheel Offset vs Backspacing
Another term that often appears when figuring out wheel offset is backspacing. The two measurements are commonly discussed together when talking about wheel fitment. While they both describe how a wheel sits once it is mounted on the hub, they measure the position differently. As we mentioned earlier, wheel offset is the measurement of the distance between the mounting surface and the wheel’s centreline. On the other hand, backspacing measures the distance from the mounting surface to the rear edge of the wheel. Together, these measurements give a clearer idea of the space behind your wheel. This space is important for suspension and brake components.
How to Measure Wheel Offset on Your Wheels
Terms like how to calculate wheel offset can sound technical. The same applies to how you measure wheel offset. However, it becomes easier once you understand what it actually shows. Running across the wheel is the centreline that marks the middle of the wheel’s width. From this point, the mounting surface shows where the wheel sits on the hub.
The distance between these two points determines the wheel offset. Usually, that figure is expressed in millimetres. It also helps to remember that wheel width is measured between the bead seats, not the outer edges. Because wheel width is measured differently, figures taken by hand may differ slightly from the standard measurements.
In many situations, measuring may not even be necessary. On many factory wheels, the offset is already stamped into the back of the wheel near the mounting surface. What you should do is just look for the letters “ET” followed by a number. This marking shows the offset value.
If it is not visible, you can still calculate wheel offset using a couple of basic measurements. To start, remove the wheel so you can measure it properly. Two measurements are needed. One is the wheel width, while the other is the backspacing.
With those numbers, wheel offset can be calculated using this formula:
Offset = Backspacing – (Wheel Width ÷ 2)
With the right wheel offset, the wheels sit correctly inside the wheel arch. This means the tyres have enough space around suspension parts, plus the guards. In this position, the vehicle can keep its natural balance. The overall driving feel also stays stable on the road.
Three Types of Wheel Offset
Positive Offset
In a positive offset setup, the mounting surface is closer to the wheel's outer face. Because of this position, the wheel is further inward toward the suspension. As such, many modern passenger vehicles use positive offset wheels. It helps keep the steering geometry aligned as designed. At the same time, the wheels remain positioned neatly inside the guards.
Negative Offset
With a negative offset, the mounting surface sits closer to the inner side of the wheel. Because of this alignment, the wheel sits evenly between the inner and outer edges. This type of offset is commonly found on off-road vehicles and modified cars. With the wheel sitting further out, the vehicle can take on a more aggressive appearance. At the same time, the load on suspension and steering components changes slightly because the wheel sits further out.
Zero Offset
Directly in line with the wheel’s centreline is the mounting surface in a zero-offset wheel. As such, the wheel sits evenly across both sides. This type of offset is less common on everyday passenger vehicles. Regardless, it still appears in certain specialised applications.
Need Help Choosing Wheels? Speak With Tyrepower
Working out wheel offset is a good place to start when looking at new rims, but it is only one part of getting the fit right. Wheel width, tyre size, and suspension clearance all play a role in how the wheel will sit once it is fitted. If you are considering aftermarket wheels, it may help to read our guide to purchasing them. You can also take a look at the wheels available at your local Tyrepower.
If you are unsure about your wheel offset measurements, our team at Tyrepower can take a closer look to guide you through your options. We can check your current wheels and recommend options that suit your vehicle.
