Wheel offset (ET or IS) is the measure of the span between the bolting face of the hub and the centerline of a wheel. It is usually measured in millimeters and stamped in the back of most rims. If the hub is flushed with the centerline you have a Zero offset. If the hub is closer to the face of the rim it's Positive, and if it is closer to the back of the wheel, it's Negative.
Let’s break down the explanation on how to calculate the offset by parts with the help of the following chart:
As you can see, the exact middle of the width of the rim (between the tire bead seat) is the Center Line.
The distance between this centerline and the bolting face of the hub is your wheel offset.
As a result, it is divided into 3 main denominations according to the hub relation to the wheel’s centerline.
ZERO OFFSET – is when the mounting face of the hub is flush or aligned with the centerline.
POSITIVE OFFSET – that is when the hub is more towards the face of the wheel. Since the hub sits towards the front of the wheel, the rim moves towards your vehicle and they have little or no lip.
Most factory OEM wheels fall in this category.
We have installed an OEM Wheel offset calculator on our site to help you with your research.
It’s a FREE tool that contains a wheel offset chart with wheels offset from all brands and models in various markets. For your convenience, we have included a link at the end of this article.
NEGATIVE OFFSET – in contrast, if the face of the hub is closer to the back of the wheel, before the centerline, you have a negative offset. In this case, the wheel sits more towards the outside of your vehicle giving you a “wide” look.
Negative offset wheels usually include wide custom rims with deep dish and aftermarket forged wheels.
Chevy Silverado with 22x10" -24 mm Negative Offset 4Play Wheels
How to measure a rim offset
How wheel offset is measured is a question easy to answer.
First, keep in mind that determining the centerline is the first step in calculating your offset. In other words, if your rim is 9-inch-wide, divide the width by 2 and you will get a 4.5-inch centerline.
Now, get your metric system ruler and measure the distance between the centerline and the face of the hub.
Finally, the result is your offset.
Now, do you have to learn all this technical stuff?
Thank god there is an easy way to find your offset without all this measuring!
Luckily 99% of the wheels in today's market, being OEM wheels or custom aftermarket rims, have the offset stamped by the factory on the wheel itself.
Look at the markings stamped in the reverse of the wheel, often behind one of the spokes. There you will see several markings like brand, manufacturing, part number and the size of the wheel.
The rims offset is most times next to the wheel size stamp, and often following the nomenclature ET (for ‘Einpresstiefe’, the German word for offset or “insertion depth”).
So, if the stamp has an ET47 you have a Positive Offset of 47 mm. In contrast, if it says ET-40, you have a 40 mm Negative Offset
A word about how important it is to get it right
To install the correct rims with the right offset is very important.
In most cases, you can have a safe difference of 3 to 5 millimeters from the offset your factory wheels came with.
However, increase that difference and you may experience a variety of problems that include:
- Wheel and tire rubbing the body of the vehicle.
- Increased risk of tire failure.
- Interference with suspension and brake parts.
- Moves the center of vehicular weight adding stress to the entire suspension system
- Increase the instability of the vehicle and poor handling.
Want to see the offset your factory wheels came with?
We’ve installed a FREE wheel and tire calculator at www.wheelsmartrims.com.
You are invited to come in and research the information by your vehicle’s Year, Make and Model, By rim size and by tire size.
You can use our calculator HERE