tolerence for tyre size on quattro.

[COT51E]

when i get my s4 (i will) i would like to boot it out with some nice euro look alloys but i may have a prob.

i know all 4 tyres have to be of the same rolling circumfrence but i have read threads about shedding rears b4 fronts thus giving a difference in rolling circumference.

the closest i can get tyre wise to fit the size of rims i want are:

245/35/17 rear on 9.5" rims
215/40/17 front on 8" rims

this combination gives a rolling difference of -1mm total from front to rear. would this be ok.

[img]modules/pnCPG/Coppermine/albums/userpics/15245/rs246_norm_keskin-kt1-gr%5B1%5D.jpg[/img]

[shineydave]

when i had my new tyres fitted i was told that the difference in tread depth had to be within 3.0mm between all 4 tyres or it would stress the diffs. not sure how that works out as a rolling figure though.

[Dippy]

Since having my S4, I have not only had different wear rates front & rear (OK I'm lazy and don't rotate as I should), but also a fair few punctures. As a result I have often had significant tread difference between front and rear (and even on the same axle, but only small and not for long).

Now I have heard a lot of "old wives" tales about keeping the tread the same on 4WD cars, but have to call them "old wives" tales because I have never seen any evidence to suggest that there will be any transmission problems. And I have searched for such evidence!

So if you only plan a 1mm difference then I have no doubt that you'll be OK.

[confusionhunter]

I personally think its a load of old rubbish for selling tyres.... It even tells you in the manual you can tow the car upto 30 miles under a certain speed with the front wheels in the air and the back on the ground... If they can cope with that they can cope with 1mm difference in tread... I have NEVER actually heard of any onw that has suffered from transmission "wind up" thats a main part of the reason the diff is there .
clue is in the name "differential"
Anyone have evidence to the contrary?
Cheers.
Mark.

[confusionhunter]

In fact this is from ELSAWIN.... (what Audi/Vw use) This should put this to bed:

When towing a vehicle with four-wheel drive and manual gearbox the following points must also be noted:

◆ Do not tow vehicle at a speed of more than 50 km/h.
◆ The maximum towing distance is 50 km.
Using a breakdown vehicle the vehicle may be towed suspended at front or rear.

Note:

If it is not possible to tow the vehicle normally, it must be transported by a special transporter or trailer. This also applies to distances greater than 50 kilometres.

[dummi]

isn't the difference in rolling radius more significant to the diff's when under load from the engine, being towed will have no power through the wheels, gears will not even be engaged?

though i agree 1 mm really isn't going to make a difference

[COT51E]

thanks guys for your replies, this gives me some pease of mind

it's not that i don't like the std wheels on the s4 i just like to be a little different from the norm and i've always liked the wide stance of the euro look. i also attend a few shows throughout the year. the std wheels will be my winter wheels.

to make things simpler i could always buy rims of the same width but have the rears with a lower ET thus giving the same appearance but this means the tyres will be matched and able to rotate.

wish i could get one now!

[COT51E]

went to the telford all types show the other week and there was a yellow TT with 19" on the back and 18" on the front but the tyre size did not tally up. can't remember the tyre sizes but at a distance they where deffo larger on the back.

tim from QR sport said the new diff set up can cope, i take it this only applies to new audi's as it was the new shape TT with that horrid new grill.

[rolskii]

@Dippy & Mark...... well I think it too could be a load of old tosh......... keeping same tread pattern, but when i got my first S4 it was a advert for square wheels and second hand tyres... car was noisy & snatchy, on rear diff mainly, put PS2 on front, dunlop sp 9000 on rears, still snatchy and crap, fitted PS2 all round and my xmission noises all stopped ....... wind up you will get on old transfer boxed 4wd(land rovers had free wheel hubs to aleviate this on front, wind up if locked on i believe right)

So in my exp. it does make a tranny snatch issues,
this is when pulling out hard from a T junction ....... noted a few times by my passengers sitting in rear over the diff too..!

Cot5ie, if you wanna rotate, make sure your tyres arent directional or you will have to get them swapped on rims every other time you rotate .... pain .....

[ZeroK66]

It's quite simple to understand why you should not have large differences in rolling circumfrence. In the good ol' quattro - the wheels are designed to rotate at the same speed. Yes torque is adjusted between front and rear - but the wheels rotate at the same speed. Now if one axle is completing a rotation quicker than the other - then this will cause agrivation in the diff as the rotating parts will be trying to spin at different speeds. You know how you wring a towel dry... thats what could be happening to your diffs/driveshafts. Obviously audi would compensate for this to some degree... (Hence the no more than 3mm difference) but long term big differences must cause damage somewhere.

The Audi TT, S3 etc - the rear wheels freewheel till the Haldex Diff Clutch engages sending power to the rear wheels and so running different size wheels is not likely to cause a problem as the clutch can make up for the difference. The clutch is only engaged fairly rarely.

[confusionhunter]

I agree, all I was saying is your car isnt going to blow up by having small tread depth differences, I would always run the same tyres regardless anyway. But generally speaking the less the diff has to do the better!