ET is an abbreviation for "einpresstiefe," which is a German term that translates to offset. It is the ET measurement that determines how deep your wheels sit in the wheel arch. A lower ET value makes the wheels extend further out in the wheel arch, while a higher ET value makes the wheels sit further inside.
You can find out what ET measurement a wheel has by looking at the backside of the wheel.
When purchasing new wheels, it is crucial to adhere to the car manufacturer's recommendations. You need to know the recommended ET for your specific car. Typically, you can deviate by about 10mm in either direction from the recommended ET. For example, if the car manufacturer specifies ET45, you can usually use ET35 if you want the wheels to protrude slightly more from the wheel arches.
A simple way to measure this distance is with a special tool featuring an offset stick. For example, the tool shown in the pictures below (US PATENT NO: 6,035,728):
With a tool like this, you first set the width of the wheel on the right scale. Then, you hold the tool against the back edge of the wheel and push down the offset stick until it rests against the back of the wheel's center (the mounting surface of the wheel). Once you've done that, you can easily read the wheel's ET on the scale near the offset stick.
Once you have these measurements, you can use the following formula:
ET = Z – (Y / 2)
Where Z is the distance between the back edge of the wheel and the mounting surface, and Y is the width of the wheel.
If the wheel's width (Y) is 244mm, and the distance between the back edge and the mounting surface (Z) is 175mm, you can use the formula as follows:
53 = 175 - (244 / 2)
So, the wheel in the example above has an ET of 53.
| Wheel width | |
| Distance to the mounting surface | |
ET = Z – (Y / 2)
