I have been told, "no cant do that mate"!!!!!!

[Straycat]

Hello, I have just got hold of a 1998 S8 with 255/45/18's on the back and 245/45/18s on the front. The front's are now on the limit and need changing, I got hold of some nearly new tyres from a mate that does track day racing in a Toyota Soarer after he changed them for track tyres but they are 245 40 18s. I have been told by the tyre fitting place that he would not fit them as my car is 4x4 with traction control as they will nacker the gearbox/transfer box????? is this correct
or will they be OK to use. I also had a word with my local Audi place and they told me to buy 4 new tyres as my car should have 245 45 18s.

Any advise will be greatly excepted.
Thanks
Mick

[Conan_the_Librarian]

Mick,

The commonly held belief is that rolling radius must be with 1% so you don't damage the quattro section of your transmission.
You currently have 1.33% difference with your set up which you may just get away with. Switching to 245-40/18 will increase the difference to 3.71% smaller on the front and you are heading for a whole world of hurt. If you want to run a staggered set up then ensure the tyre's rolling radius is within 1%.

I have a staggered set up on my projekt of 285/30-20 rear and 245-35/20 front. .07% difference, works fine. The arches are modified. Workable combinations and wheels for our cars is here.
(http://www.audipages.com/upgrades/tiresizeoptions.html)
There is a good calculator here (http://www.carbibles.com/tyre_bible_pg4.html) and lots more information besides.

HTH

[Straycat]

Thanks for the info.
Blimey, so there not just rubbery things on each corner there is science behind it. :rolleyes:

So if I keep them all the same size on all four corners I guess that will be ok? The backs are nearly new so don't want to change them if I can help it. (255 45 18) so I will have to go and get some new 255's My mate with the track day car said about trying FALKEN tyres, are they any good bearing in mind it is a family drive not a track car and then only really used at weekends as I have a work van during the week.

[Conan_the_Librarian]

Try to keep the same make / model of tyre on all four corners if possible. If not Falkens are a good mid range tyre. +++