quattro allowing different roll diameter

[bloodredsmurf]

Hello, new to the community and will be putting 18x8.5/9.5 on my b5 s4. Just rolled my fenders and was thinking about what tires to run. Was going for 205/40 front and 215/40 rear. Will my diff allow me to use these two tire "circumferences?" I can't seem to find a calculator that will compensate for a stretched tire. All help would be appreciated. TIA

Pat

[Francois Dillinger]

i believe willtheyfit.com will have the info you need.

[bloodredsmurf]

Thanks. That is what I was looking for, as far as the circumference calculator goes, but do you know about what the quattro system will allow as far as the difference goes?

[MC Hammered]

As long as you stay within 3% of the rolling circumference between the tires you will be fine.

[Francois Dillinger]

I thought it was 2, but yeah...something along those lines.

[Uberwagen]

3% is fine. FWIW I am running 205/40 on an 8.5 and 225/40 on 9.5

[bloodredsmurf]

Uberwagen, do you have a pic you can post of that. And out of curiosity, why 225/40 instead of 215/40?

[aar0n.]

Wrong wrong wrong!! Quattro allows for 0% difference in rolling diameter front and rear. Haldex, which is used in R32s and TTs, allows for up to a 4% difference but Quattro does not.

Additionally, stretching a tire does not have any effect on overall tire diameter. Tires are steel-belted and stretching affects the shape of the sidewall but has no effect on the actual diameter as the steel belt does not change in size.

[bloodredsmurf]

So in a nutshell, I won't be able to use the tire sizes that I listed above.

How is that possible when plenty of people have small differences in front and rear size roll diameter?

Like uberwagon running those different sizes

[Pyropiggy2.5]

I'm sure it would still drive fine

Just not as well as with all 4 of equal diameter

But, if you're looking for that much stretch, I doubt performance driving is an issue

[Tuck&Poke]

Wrong wrong wrong!! Quattro allows for 0% difference in rolling diameter front and rear. Haldex, which is used in R32s and TTs, allows for up to a 4% difference but Quattro does not.

Additionally, stretching a tire does not have any effect on overall tire diameter. Tires are steel-belted and stretching affects the shape of the sidewall but has no effect on the actual diameter as the steel belt does not change in size.

Yea, pretty much. It can cope with treadwear differences of 4/32, but that's about it. Since its torsen based, there isnt much room for difference at all.

So in a nutshell, I won't be able to use the tire sizes that I listed above.

How is that possible when plenty of people have small differences in front and rear size roll diameter?

Like uberwagon running those different sizes

Just because someone on a forum does it, doesn't mean you should. People on forums do lots of stupid shit all the time.

[MC Hammered]

Wrong wrong wrong!! Quattro allows for 0% difference in rolling diameter front and rear. Haldex, which is used in R32s and TTs, allows for up to a 4% difference but Quattro does not.

Additionally, stretching a tire does not have any effect on overall tire diameter. Tires are steel-belted and stretching affects the shape of the sidewall but has no effect on the actual diameter as the steel belt does not change in size.

Quattro does allow for a variance in tire circumference.

Less than 1% is optimal, up to 3% it the max suggested threshold.

[aar0n.]

Quattro does allow for a variance in tire circumference.

Less than 1% is optimal, up to 3% it the max suggested threshold.

No it doesn't. Everything I have ever read about Quattro says otherwise. Sure you can run different sized tires but don't come back complaining when your diff blows up

[MC Hammered]

So when someone has one tire fail Audi expects everyone to shave their new replacement tire down to match the other 3 worn tires, or buy 4 new ones? Never mind that the spare in the trunk might not match the tire sizes that are currently bolted on the car.

People on the Audi forums run staggered setups all the time and the 3% threshold is used when sizing the tires. Using the tire size calculator and selecting the correct tires will put you within 1% and we wouldn't be having this discussion.

[SeanDub]

Every tire shop recommends that you buy 4 tires when replacing tires on an awd car.