Running Two Different Tyre Sizes... Help

Gmac

Registered User
Needing help/thoughts...

Looking at getting winters for the S3 8l and I've seen 2 x 225/45/18 and 2 x 225/40/18

So I was wondering if this would be ok to run with the haldex on the S3.

Would these calculations be correct....

225/40 = 225mm width and side wall 40% of this so 22.5 x4 = 90mm ie 9cm for side wall (4.5 top 4.5 bottom)

225/45 = 225 width and side wall 45% of this so 90mm + 11.25mm so 101.25mm ie 10.12cm

So 1cm different? (.5cm top and .5 bottom

Tia
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M

monopole

Guest
I'm sure they would be fine on different axis, but you need better advice than I could offer on this
 

snowy

Registered User
The ABS unit's speed sensors will detect the axles turning at different rates and assume slip

It might try to do all sorts to fix this - eg using brakes or more power to rear axle

You can use any width combo, but circumferences of wheels on both axles has to be the same
 

Gmac

Registered User
Great, cheers snowy! I'll just get the 225/45's and keep an eye out for some more of the same! Thanks folks!:arco:
 

Alex C

Well-Known Member
VCDS Map User
When the 225/45 are doing 62.4mph the 225/40 are only doing 60.3,mph, so one set of tyres are walking slowly away from the other pair and subsequently the Haldex works overtime
 

RobinJI

Registered User
Sounds like you're not going to try it anyway, but just for future reference, the size calcs are correct, but that's for each side of the wheel. So a 225/40 has 9cm top and 9cm at the bottom as well.

(I'm not sure on this, but isn't the standard S3 size 225/45r17, so surely a 225/45r18's going to be an inch too big? I'm sure someone will know.)
 
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