Can you run 255/40R18's on 7.5" rims?

[itchingtogo]

I have a RS6 with RS6 rims that I just discovered are 18" x 7.5". The manual said that they should be 8.5" and the tire Mfg. spec. sheet says that the min rim size is 8.5". They look to be OEM so what gives? Are these "snow" rims? http://www.rs6.com/forum/../smilies/headkratz.gif

[skiwi]

you shoiuldn't. usa normal is 8.5 with 18's. it's 9" with the 19's for the same 255 fitting for most of the rest of us...

[Buff-Daddy]

Those are the dimensions of the RS6 snow tire option.

[itchingtogo]

SO they are OEM but are made for the 225/45r18 M/S that is shown on the tire sticker?

[Buff-Daddy]

Yes, I believe it was a no cost option at time of purchase.

[itchingtogo]

Does anyone know what the outside width dimention is on a 7.5" or a 8" or a 8.5" ? I measured mine and they appear to be 8.5" rims with a outside dim. of 8.75" or so.

[Skaala]

I run 245/40/17 on the RS2 on a 7'' rim, and they were a pain in the ass to get on! :)

[skiwi]

the only legal fitment of a 245/40 for the rs2 is the homologated dunlop sp8000. any other fitting will cause excessive heat build up in the sidewalls due to "bagging". i blew out a bridgestone s02 due to this cause on my rs2 but got my money back from the tyre shop because they should never have fitted the tyres in the 1st place. btw, the factory manual makes this quite clear...

standard fitment on a 7" rim would be a 225. it will improve the handling of the car as the sidewalls will work as intended. btdt.

remember - regardless of the tyre dimensions, you have exactly the same amount of rubber on the road (200, 225, 245, 255)...

[Leadfoot]

I many years ago run a tyres fitting business and one thing you should never ever do is over-tyre a rim, as skiwi said heat will build a lot quicker plus the car will wander all over the road. For a 7.5" rim the right tyre choice would be 225~235 and for 8.5" it would be 235~245 but this also depends on the ratio of the side wall, the higher the side wall the narrower the tyres.

Hope this helps.:thumb:

[Skaala]

the only legal fitment of a 245/40 for the rs2 is the homologated dunlop sp8000. any other fitting will cause excessive heat build up in the sidewalls due to "bagging". i blew out a bridgestone s02 due to this cause on my rs2 but got my money back from the tyre shop because they should never have fitted the tyres in the 1st place. btw, the factory manual makes this quite clear...

standard fitment on a 7" rim would be a 225. it will improve the handling of the car as the sidewalls will work as intended. btdt.

remember - regardless of the tyre dimensions, you have exactly the same amount of rubber on the road (200, 225, 245, 255)...

hmmm.... crap.. the tyre shop didn't say anything when I ordered the new ones. The old ones were dunlops, but I couldn't get a hold of them here in Bergen, and I went for Goodyear Eagle F1's. I have driven it a few trips to my cabin, a 500km fast drive on twisty roads, and the tires have performed excellent, but if there is a danger of blow-outs.....crap.. the tyres weren't exactly cheap, and I doubt I will get my money back, as I got them on a last sale before the model ended, and I had a pretty good discount.

I have been thinking of upgrading to the 18'' Porsche Turbo Cup, so I'll have to try and find someone who needs the F1's then.

[skiwi]

i would try your luck with the tyre shop. if they had used any audi fitment guide, it would have been clear. if not, then audi has an issue...

if you stick with the 17's, go with 225's - they will transform the car.

btw, i am a big fan of the goodyear f1's for a quattro...

[Skaala]

i would try your luck with the tyre shop. if they had used any audi fitment guide, it would have been clear. if not, then audi has an issue...

if you stick with the 17's, go with 225's - they will transform the car.

btw, i am a big fan of the goodyear f1's for a quattro...

well.. turns out is both of our faults...he did mention that the tyre was very wide for such a rim, but I went to the car and got the registration where it says that 245/40/17 is the standard dimention. They didn't have any messages about the RS2 having a "special legal tyre". They had sold several 245 so other RS2 owners, and none have had blowouts. thankfully. I just wanted to make sure that I got the right standard dimention. I realise now, that if I had checked a bit around the internet at different forums, there are a lot of people driving on 225. well well.. it has performed excellent for now, and porsche turbo cup 18'' are on the wishlist.

[skiwi]

yes, unfortunately the warning is only in the audi workshop manual, not the drivers manual...