Have I made a total c*ck-up?

[benjie]

Had a rather spectacular tyre blow-out today. Not fun on the M4 at 6.30am. Ive already ordered a pair of new tyres, due for fitting Friday. I've just checked & noticed I've ordered the wrong size. On the back I have 235/40/18 and on the front I will have 235/45/18 - a 5% difference in the aspect ratio. Will this have a negative effect on the car…it's quattro & I don't want to ruin the diff.

 

[DieselJake]

It'll knock the speedo out a bit but it's not the end of the world, ask to change for the same set of tyres though if you can.

 

[desertstorm]

From what I have read certainly not adviseable to run different size tyres front an rear on a proper quattro car with a torsen diff.
Tyre Size Calculator - Legal Requirements - Etyres says there is 3.7% difference in the diameter which translates to the 235/45 tyre being 24 mm bigger in diameter than the 235/40 . So the car will have 12mm more goround clearance at the front and it will be quite noticeable i would have thought.
The manual says all wheels should have tyres of the same make, tread pattern and size, I think thats taking it a little far.
Other posts I have seem where people are unning staggered set ups seem to indicate a 3% difference at maximum is OK.
As you are outside of event that and there is a noticeable difference in the size I would say don't fit them.

Karl.

 

[Mike.M]

I would try and cancel/exchange the order with the 40 profile myself

 

[benjie]

Thanks for the input guys, just wanted to check. I'm going to replace all of them - better to be safe than sorry. I was planning on it after Christmas anyway.