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Wheel offset

Serhii Maslov Section: Wheel offset (ET) Updated: First published:

What is wheel offset?

wheel offset, different options Wheel offset is the distance between the wheel’s vertical plane of symmetry and the wheel’s mounting face against the hub, in millimetres. The formula for working out a wheel’s offset is extremely simple:

ET=a-b/2, where

a is the distance between the wheel’s inner face and the wheel’s mounting face against the hub

b is the overall width of the wheel

From the formula it is easy to see that a wheel’s offset can be positive (most often), zero or negative. What’s more, a wheel’s offset directly affects the track width, because this parameter directly determines the distance between the centres of symmetry (across the width) of the wheels on one axle.

The same formula leads to another conclusion: a wheel’s offset is affected by neither the width of the wheel (and, accordingly, the tyre) nor its diameter. What matters for working out the design loads on the suspension is only the lever arm, that is, the distance from the centre of the tyre (across its width) to the hub. So, regardless of the size of the tyres and wheels, the offset the car was designed for, which the manufacturer specifies for one particular model, is always the same one figure.

In the markings stamped on the inner face of the wheel, offset is shown as ETxx, where xx is the actual offset figure in millimetres. For example: ET45 (positive), ET0 (zero), ET-15 (negative)

Can you fit a wheel with an offset the car maker does not list, and why? (Everything about wheel offset.)

More on this topic

Spigot rings for wheels: everything you need to knowOpinions on spigot rings are divided: some say they are unnecessary, others that they are absolutely essential, and of good quality at that. So which is it? How do you choose spigot rings?If a wheel’s centre bore does not match the size of the hub’s spigot, the problem can be solved by fitting special spigot rings, which are sold at tyre centres. Wheel markingsWheel markings. What is stamped on a wheel? The main markings on a wheel usually look something like this: 6.5J x 15 5/112 H2 ET45 d 57.1. Can you use wheel spacersUsing wheel spacers this way is more or less justified (with the caveats below), but only on condition that the spacers reduce the wheel’s offset exactly to the standard figure (the one the car maker… Why does a wheel need a centre bore?The centre bore, and the centre bore alone, is what a wheel needs for fitting correctly onto the hub, not the tapered seats on the bolts (or nuts), whatever some sellers may claim. Why are there tapered seats on wheel bolts and nuts?The tapered seat on wheel bolts (or nuts) is not designed to, and cannot, guarantee precise centring of the wheel on the hub.