In the process of searching and buying new wheels for your vehicle, one of the most critical factors to look at is the Wheel Offset. At CNC Wheels, customers commonly ask us “What wheel offset do I need?”. As there are many vehicle makers and models in the market, the wheel offset you’ll need depends on the vehicle, as well the width of the rim you want to fit on. In more technical terms, it is vital to understand what wheel offset is and how it works; so that the right decision is made before you purchase wheels.
Wheel Offset Explained
Zero wheel offset is the point at which the centre mounting surface is in accordance with the centreline of the wheel. In other words, a zero offset is when the mounting surface of the wheel is on the centreline. This implies that the two of them line up and that there is no contrast between the wheel itself and the wheel curves. A zero offset wheel is frequently alluded to as wheel with ET0.
Positive wheel offset is the point at which the mounting surface is towards the front of the wheel (mount further inward on your vehicle). Positive offset gives more clearance from the outside edge, but it will also reduce the space between the inside edge of the tyre and suspension. Looking at the wheels from the front, wheels with positive offset typically have a flat surface or in some cases a minor concave shape or dish.
Negative offset is the point at which the centre mounting surface is behind the wheel centreline. This indicates that the mounting face of the rim fits lot further into it, which increases the inside space between the inside edge of the tyre and suspension. For upgraded cars or lifter trucks, it’s important to select a less offset from OEM to get more clearance. Using deep dish wheels or deep concave wheels as an example, those wheels are typically fitted in a negative offset.
Common Issues Choosing Too Much Positive Offset
- Push the wheels and tyres too far inside the wheel arches.
- Tyre rubbing over the bodywork or suspension.
- Decrease vehicle handling
- Interfering brake parts.
- Unstable handling.
Common Issues Choosing Too Much Negative Offset
- Push the wheels and tyres too far outside the wheel arches.
- Extra load on the suspension.
- Cause tyre vibrations.
- Increased steering wheel kick-back.
- Decrease in vehicle handling.
How To Measure Wheel Offset?
The least demanding approach to find out the offset of your rim is just to flip it over and examine the back. By far, most of wheel brands will stamp the offset number on either the mounting centre or on one of the alloy wheel spokes.
Now that we know where to find offset on rims, we ready to start reading the numbers on the wheel to get details on size and configuration of the rim. This information is essential to determine if a wheel will fit your vehicle.
17×8.5 refers to the size of the wheel. 17” is the diameter and 8.5” is the width of the rim. ET38 refers to the offset of the wheel. ET is a German abbreviation for Einpresstiefe, which means offset. This number can tell us the rim is 38 millimetres from the centreline.
In the event that for reasons unknown your wheel doesn’t have an ET number stamped, you can measure it by following simple steps as stated below:
- Use mm metric to measure the overall width of the rim.
- Locate the middle line of the wheel, accurately half of the wheel’s width.
- Measure the distance from the back edge of the wheel to the mounting face.
- Take the distance of the middle line away from the distance between the back edge and mounting face.
- Great! You have just measured the offset of your wheels.
We already understand that wheel offset is the distance from the centre of the wheel to the mounting face. So the question is, what is wheel backspacing? Wheel backspacing refers to the measurement of the distance from the inside edge of the rim to the mounting face. Put simply, it’s the space in the back of the alloy wheel.
When you reduce backspacing, you get more inside rim clearance. This means that less backspacing results in a lower amount of the wheel in the wheel well. As the amount reduces, you lower the risk of the rim rubbing the suspension or brakes.
When you increase backspacing, you get less inside rim clearance. The more backspacing you have, the more of the wheel is in the wheel well. As the amount increases, the chance of the rim rubbing over the suspension or brakes. You definitely don’t want that.
For lifted trucks, backspacing is particularly vital aspect to look at. Truck owners, pay attention to the limited backspacing allowed by the manufacturer of the lift kit you purchase. If you decide to go with bigger rims and choose a wheel with too much backspacing, the rim won’t fit on your truck. Make sure you always know the limited backspacing allowed for your lift kit.
You can calculate backspacing in inches as followed: Wheel width ÷ 2 + offset + ½” = Backspacing.
Why Are Offset And Backspacing Measurements Important?
Any vehicle owner needs to understand that proper offset and backspacing measurements are quite critical in their importance. The appropriate measurement of the wheel offset is vital for the appearance and fit. For instance, if you are installing new and larger wheels and tyres to your vehicle; a higher offset means that the outside edge will be higher for your vehicle giving more clearance, but the space between the suspension and tyres will be decreased, and it can cause problems if this space is not measured correctly.
Similarly, the correct measurement of a backspace is also essential. More backspacing indicates that wheels will be closer to the suspension and brakes. Less backspacing would mean that wheels are away from the suspension and brakes with less risk of rubbing. This backspacing measurement needs to be correct while choosing rims and looking for the best fit for your vehicle.
Picking The Right Offset
Picking the right offset is not a hard task, but it has to be current. You can find the right offset of your vehicle by looking at the markings on your existing wheels. If you want to change your wheel size or width, trust CNC Wheels for the perfect fitment every time. We can ensure that your wheels will fit their correct PCD pattern and offset.
Still got questions about choosing the right offset? Just contact CNC Wheels at [email protected] or via our online LiveChat support.
Remember This About Wheel Offset And Backspacing
- New wheels can make your everyday ride look and handle a whole lot better.
- Offset can be tricky to choose. If you pick the wrong offset, it can decrease your vehicle stability.
- If you change to wider than the OEM, backspacing has to be factored in along with offset.
- Make sure your new wheels fit currently within the load capacity of your vehicle to provide you the handling and stability you need.
Want to see some options that will fit your vehicle? Browse wheels suited for your vehicle’s make and model.