AvramD

Hey out there... I'm an S4 owner (and frequent the S4 forum).

To make a long story very short, I need someone to measure the actual circumference of an A8 tire with one of the following sizes:

225/60 16
245/45 18
225/55 17

I need to compare it to the circumference of an S4 tire, which is 225/45 17. Mine measures 79.5 inches, or 2020 mm. I measured it by extending a tape measure in front of a front tire (the long way, and driving over it. Then I wrapped it around the tire.

Why do I need to do this? You can read the whole story on the S4 forum at the link below. Basically, my dealer replaced a bad Nav computer in my S4 w/ a unit from an A8, and it is programmed w/ an A8's tire circumference. When they tried to reprogram it, they found that their tech CD only has numbers for A8s. It doesn't say what the formula is, and AoA says the info hasn't been released yet.

So, I am trying to use geometry to figure out what the formula is, but I'm coming up w/ numbers that are about 3% off from the AoA tech CD. Now I'd like to compare actual measured circumference to the CD chart as a way to verify the numbers my formula is producing.

Yes, I know this should be Audi's problem, but they're not solving it. "If you want it done right, you gotta do it yourself."<ul><li><a href="https://www.audiworld.com/forum/m/s4/25287.phtml">Need help from someone w/ an S4, Nav & VAG 1551/1552, or...</a></li></ul>

Just me

Why can't the dealer obtain this information - no A8's on the lot

Bill Mills

I come up with 82.5 inches with the stock 225/60 16 Eagle LS tire on the stock Audi rim. This was measured with the tire/wheel off the car.

Reggie

Dunlop site has exact measurements for all size tires.