21" wheel and tyre size

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Joined: Wed Oct 13, 2021 10:32 am

Post by q4Ricky » Wed Oct 13, 2021 6:21 pm

Hi All,

Doing some research around the 21" wheel and tyre selection for the Q4

For anyone into the finer detail of their chosen cars?

Does anyone know why Audi have chosen to use the following sizes..

Front - 21" x 8.5 J rim, sporting a 235 x 45 x R21 tyre

Rear - 21" x 9 J rim, sporting a 255 x 40 x R21 tyre

Looking at tyre manufacturing outputs and they recommend the following, but do say as a minimum a 235 tyre can be used but not recommended.

Front - 21" x 8.5 J rim, sporting a 245 x 45 x R21 tyre

It would of made sense to keep the rims and tyres the same size, with simplification in mind? or is there a good reason for this?

Cant think of any good reasons, but hoping someone can assist in shedding some light on this..

Hoping this will start some good conversation between members of the forum?


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Joined: Wed Oct 06, 2021 4:35 pm

Post by hugodoodle » Thu Oct 14, 2021 7:08 am

I believe they may have chosen the wheel and tyre sizes for the following reasons:
  • Rear traction and mass distribution across the tyre, especially under acceleration at gross vehicle mass may be an issue and exceed tyre design limits.
  • The ride and loading requirements for the front will be less, so Audi could stick with a thinner wheel and tyre, which will be a little cheaper and better for rolling resistance.
  • The front sidewall is about 5% higher than the rear which may help with ride and steering comfort and reduce the likelihood of tram lining on a large wheel.
Q4 50 Quattro C+S

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Post by johnd » Thu Oct 14, 2021 8:22 am

Several makes/models have different front/back tyre specification - my old Porsche Macan for one. In fact, it's surprising that more models don't do this - as above, the design parameters and priorities for front and back can be significantly different. But I suppose that the simplicity of having the same all the way round is considered to outweigh the potential benefits to traction, ride comfort, steering feel etc. But it does seem to be more common amongst EVs I've noticed, especially the ones with higher performance.

Posts: 16
Joined: Wed Oct 13, 2021 10:32 am

Post by q4Ricky » Thu Oct 14, 2021 9:20 am

Thanks all,

Appreciate your personal thoughts on this subject.

will let you all know, how I get on with my review in further posts..


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