How to calculate wheel offset

[Oversize]

This seems a mystery to many, however it’s really rather easy to determine. Easiest is to find the marking on the wheel following ‘e’ or ‘ET’. However some wheels aren’t marked or it’s no longer readable. This works with or without a tyre fitted.

Turn wheel face down on a flat surface,

Use straight edge (a spirit level works well) and lay it flat across the extremities of the wheel or tyre,

Measure distance between lower surface of straight edge & floor,
Half this distance = Wheel Centre,

Measure distance between lower surface of straight edge & wheel hub surface,

Subtract smaller value from larger one = offset value.

If the Wheel Centre is the smaller value then your offset is +

If the Wheel Centre is the larger value then your offset is -

You’re welcome!

 

[Michel]

Excellent reading and very simple to understand.
Thanks Mark

 

[Patrick_R]

Nice information mate.
Thanks for sharing.

 

[Oversize]

Don’t forget that offset isn’t the only issue when considering new wheels. The incorrect shape of the spokes can foul on calipers (eg series 1 vs series 2 Pentas) and wheel bolt holes are often larger on later model wheels. Meaning early wheels won’t fit later cars. A shallow hub depth can result in the inability to refit hub centres/caps since later cars used sealed wheel bearings. So in the end the wisest option is test fitting before purchase.

 

[ProfessorExperimental]

Not to mention centre bore diameter (use hubcentric rings if wheel CB > original wheels, aluminium from eBay are ok but sometimes hard to fit, polymer from hubcentric-rings.com were the first I found readily available and imo still the best, plus they're marked), and the (in Germany anyway) evergreen distinction between "kugelbund" and "kegelbund": spherical vs conical seat lugnuts/bolts.

MB is afaik all spherical, but most other countries/marques are predominantly conical seat, and this includes almost all aftermarket offerings. You'll also run into the occasional stepped lugnut hole, with what appears to be an extremely narrow conical seat, these require a precise shank on the nut to mate properly, quite similar to the flat-mating-must-use-washer cragar-style aftermarket wheels on old muscle cars.

Then there's the occasional "bolt/nut fits in hole, but my socket won't, wtf?" chestnut. My amg aeros were the first I've seen like this, with an elongated bolt where the seat is about 50mm inboard of the hex head, so a normal wheelbrace can handle it. Pity the person who scored the wheels cheap without the bolts to match...