3 series F30 to F34 GT Wheel & Tyre Sizes - Help

[G9NJE]

Ive just bought a 2015 BMW 325D GT Gran Turismo F34 and want to change the wheels and im bit of a novice but do understand the basics and the consequences of incorrect sizes etc.

I have tried to look it up on various threads but I haven’t managed to find an answer.

I’ve done my homework and would ideally like someone to validate what I’m thinking, or tell me ive missed something or totally barking up the wrong tree and answer the bits I’m not sure about.

Ive gone on a bit but want to cover everything I think I know.

I want to fit 20” BMW 404m wheels off an F30 3 series.

From what I can gather the whole wheel circumference is different from standard between the standard 3 series (F30 – 26’) and the GT (F34 – 27”)

This obviously results in bit of an issue when bolting the F30 wheels on


Standard wheel and Tyre sizes for my F34 GT

Front 225/50R18 - 8Jx18 ET34

Rear 255/45R18 - 9Jx18 ET42


Standard wheel and tyre size for the F30 404 wheels

Front 225/35/R20 – 8Jx20 ET36

Rear 255/30/R20 – 8.5Jx20 ET47

I have put these through an on line calculator and the differences are

Front – 2.5%, out so will be recording displaying a higher speed and more miles than it should be, and ride height reduced by 8.35mm

Rear – 3.89% out so will be recording displaying a higher speed and more miles than it should be, and ride height reduced by 8.35mm

Ive had a play around with the profile of the tyres in the calculator and have come to the following solutuin which im pretty happy with.

Front 225/40/R20 - Difference is -0.84% so will record slighty lower miles/speed and raise ride height by 3mm, but thats as close as I can get it

Rear 255/35/R20 - Difference is 0.03% which is obviously negligible.

I’ve read it its withn 1% then its fine?

In terms of offset they are only 2mm different on the front and the same width so cant see that being an issue, but 5mm different on the rear so that sounds like it should be ok, however I don’t know what impact the width of the wheels has on this as the rears will be 0.5j narrower than the standard wheels.


Any thoughts/advice would be really appreciated.