Tyre alloy question urgent

[badmaash]

Hi All I am taking the standard S8 alloys of as one is slightly buckled amg puting 19inch rs4 alloys the 9 spokes on. The alloys are of my mates car with a size of 235/35/19. I know the standards are 245/45/18 would this make a big difference and aslo would it be alrite going to a smaller tyre width on an S8.

[S4_Dan]

245 is the standard width on S8/QS and prob all other 8's, not sure about reducing the tyre width. I think this would hinder the grip/traction somewhat especially in the wet!

The tyre wall reduction from 45 to 35 'may' stiffen the ride a little but shouldn't be too bad.

Personally, I'd get the same width alloys at fron and maybe some 275's for the rear. Thats my 2p's worth.

[Muppet_man]

It is important when having tyres to keep the rolling radius of them always the same. i.e. the distance of ground that the tyre covers in one revolution.

The equivalent to 245/45/18 in 19" using the 35 series profile you mention would be 275mm wide. This then means that the 35 (which is the percentage of the width of the tyre that makes up the hight) would be the same as your old tyre. So the ride wont suffer generally.

245/40/19 would also be the same.

Having a different rolling ration would effect your economy, speedo, acceleration times and also your auto-boxes gear-change as this is based somewhat on speed.

Hope that lot helps.

[NickGUK]

Hi, you can quickly see the sizes that equal out each other using this small table i have, it will calculate different wheel / tyre sizes and give you the diff in the overall diameter which is what must be kept the same

Tyre / wheel size calculator

[S4_Dan]

Acording to the calculator posted by NickGUK, the difference is 4.57%. Recomended difference is give or take 2.5%.