Offset (ET for short, from German "Einpresstiefe") is one of the most important factors when buying rims: it determines how far the wheel sits in the wheel arch – and thus affects track width, clearance, handling, and whether a rim is even permissible for your vehicle. This guide will provide you with a concise and understandable explanation of what ET means, how to read and calculate it, how it impacts your vehicle, and when registration is necessary.
1. What is Offset (ET)?
Offset is the distance in millimeters between the mounting surface of the rim (where it sits against the wheel hub) and the center of the rim. It determines whether the wheel moves further inward into the wheel housing or further outward. There are three cases:
| ET Value | Mounting surface is … | Wheel sits … |
|---|---|---|
| Positive ET (e.g., ET45) | in front of the rim center (outward) | further inward in the wheel arch |
| ET 0 | exactly at the rim center | centrally |
| Negative ET (e.g., ET−12) | behind the rim center (inward) | further outward (deep-dish look) |
Rule of thumb: The smaller the ET (down to negative values), the further the wheel protrudes outwards. The larger the ET, the further it moves inwards.
2. Where can I find the offset?
The ET is usually stamped or cast directly onto the rim – most commonly on the inside of the spokes or on the wheel face, e.g., as "ET45". It is also listed in the certificate (ABE or parts certificate) and in the product description of reputable dealers. The factory-approved values for your vehicle can be found in your vehicle documents or the CoC document.
3. Calculating Offset
If no marking is legible, the ET can be determined from two measurements:
- Measure the overall width of the rim (from flange edge to flange edge) – the center of the rim is exactly half of this measurement.
- Measure the distance from the mounting surface to the inner flange edge.
The ET is then the difference between the distance of the mounting surface and half of the overall width. Important: The embossed inch width (e.g., 8J) is the jaw width, not the overall width – for the calculation, the actually measured dimension counts. In practice, reading the embossed ET is almost always the simpler and safer method.
Calculation example
Suppose you measure an overall width of 220 mm on a rim – the center of the rim would then be at 110 mm. The distance from the inner flange edge to the mounting surface is 155 mm. The offset is 155 mm − 110 mm = ET 45. If, however, the mounting surface is only 98 mm from the inner edge, the ET would be 98 mm − 110 mm = ET −12 (negative), meaning the wheel would protrude significantly further outwards.
4. How does offset affect the vehicle?
The ET influences several areas simultaneously – which is why it's more than just a number on paper:
| Area | Small/negative ET (wheel protrudes outward) | Large ET (wheel sits inward) |
|---|---|---|
| Track width | wider | narrower |
| Appearance | sporty, flush/deep-dish | subtle, deep in the wheel arch |
| Outer clearance | can rub on the fender | uncritical on the outside |
| Inner clearance | uncritical on the inside | can rub on strut/brake |
| Steering/bearings | higher load, altered scrub radius | closer to stock condition |
Therefore, a changed ET directly affects track width and clearance. If the wheel protrudes too far outwards, the tire can rub against the fender; if it sits too far inwards, contact with the strut, brake caliper, or chassis components is a risk. Excessive deviations can also place greater strain on wheel bearings and steering.
Specifically calculated: If you change from ET 45 to ET 35, each wheel moves 10 mm outwards – the track width per axle therefore increases by 20 mm. Such changes quickly have a striking visual effect, but must match the clearance in the wheel arch and the approval. Small ET differences of a few millimeters are often uncritical, but larger jumps should always be checked against the certificate.
Consider offset and rim width together
ET and rim width are interconnected: a wider rim with the same ET will extend slightly more on both sides, thus adding to both the inside and outside. If you mount a wider rim, you often need to adjust the ET to ensure the wheel still moves freely. For vehicle approval, rim width and ET are always considered as a combination – a permissible ET value applies to a specific width. Therefore, always check both values together against your vehicle's specifications.
5. Correcting incorrect offset: Spacers and wheel spacers
If a rim's ET is not exactly right, the wheel track can be adjusted outwards with spacers or wheel spacers – they effectively reduce the effective offset. This is a common way to achieve a flusher appearance or more inner clearance. Important: Wheel spacers change the track width and generally require registration. You can find more information on this in the guide to centering rings and spacers.
Conversely, an ET that is too small (wheel protrudes too far outwards) cannot simply be "corrected" inwards – in this case, only choosing a rim with a suitable, larger ET will help.
6. Offset, approval, and tolerance
Whether a specific ET can be used on your vehicle is determined by the rim's ABE or parts certificate. These documents list the approved combinations, including permissible ET and any conditions. There is no generally applicable "allowed tolerance" to the standard ET – what the documents approve for your vehicle is always decisive.
If the chosen combination deviates from the specifications or if no suitable certificate is available, an inspection and registration at an officially recognized inspection body is required. How this works is explained in the guide Registering Rims; background information on ABE and certificates is provided in the guide KBA Number on Rims.
7. The correct offset when buying rims
To ensure the new rim fits and can be legally driven, it's best to proceed as follows:
- Check vehicle specifications: permissible ET (and rim width) according to papers or certificate.
- Note other dimensions: In addition to ET, the bolt pattern and center bore must also match; don't forget the correct load index.
- Tires and clearance: ensure that the wheel and tire run freely in the wheel arch – even when steering and compressing the suspension.
- Secure documents: Keep the ABE or parts certificate, and plan for registration if necessary.
In the zrshop, you'll find rims and complete wheels with the appropriate information on ET, bolt pattern, and approval for numerous vehicles – pre-assembled and balanced.
Discover suitable rims in the zrshop now →
FAQ: Frequently asked questions about offset
What does ET mean for rims?
ET stands for "Einpresstiefe" (offset) and describes the distance in millimeters between the mounting surface of the rim at the wheel hub and the center of the rim. It determines how far the wheel sits inwards or outwards in the wheel arch.
How do I find out the offset of my rim?
The easiest way is to read the embossed marking (e.g., "ET45") on the inside of the spokes or on the wheel star. Additionally, the ET is listed in the rim's certificate. If nothing is legible, it can be calculated from the rim width and the distance of the mounting surface.
What does a negative offset mean?
With a negative ET, the mounting surface is behind the center of the rim, causing the wheel to protrude further outwards – typical for the deep "deep-dish" look. Such combinations require sufficient clearance and appropriate approval.
How much can I deviate from the standard offset?
There is no general tolerance. What is permitted is what the ABE or the parts certificate of the rim approves for your vehicle. Deviations without suitable documents must be registered at an officially recognized testing center.
What is the difference between ET45 and ET50?
With ET50, the mounting surface is 5 mm further out than with ET45, meaning the wheel moves 5 mm further into the wheel arch. This changes the track width and clearance accordingly. Whether the difference is permissible depends on the approval for your vehicle.
Can I compensate for an incorrect offset?
An ET that is too large (wheel sits too far inwards) can be adjusted outwards with spacers or wheel spacers – these usually require registration. An ET that is too small, on the other hand, cannot be corrected inwards; here, a rim with a suitable ET is necessary.
Sources
- Fundamentals of rim technology – Offset (ET), rim center, and mounting surface
- Road Traffic Licensing Regulations (StVZO) – §19 (Vehicle modifications)
- ABE / Parts certificate of the rim – approved offsets and conditions