Have 2004 A6, 2.7T quatro. Been having tire issues. Third set comming up. The inside of the tires are getting eating up (rubbing) against ??? don't know, and the tires are cracking. 235/45R-18. the parts content information sticker listed allow wheels in 235/40 R18 high offset. Firestone has already taken me for two sets, by selling me 235/45R-18 tires. could this be the problem. the 45R instead of the 40R. Only the front tires are getting eating up, and I rotate them and have them balance, including front end aligment at least 2/3 times a year.

 

I show your car could have as an optional Audi tire 235/40/18 and uses 8x18 inch rims with 43mm offset. So you aren't far off from stock sizes. The 45 vs 40 on the sidewall profile, or height, means the sidewalls of the tires on your car are 45% the width (taller sidewalls) of the tire compared to what you should have. The height of the sidewall should be 40% the width of the tire. This difference isn't that much of a problem unless the offset on your wheel is wrong. If you have aftermarket wheels it's possible the offset is not close to what the car was designed to use, or the rims are 6.5-7 inches wide and that balloons out the sidewalls. Meaning the tires are way too wide for the rim.

I would guess the tire is offset towards the inside of the wheel well, and that could interfere with the sidewall clearance, maybe the tread surface if the wheel liner was hitting it at full lock left to right, maybe. Sounds like your alignment is good, or the shop that does it is not using the right specs but I'm sure that's not the case. If the shop doing the alignment 2-3 times a year hasn't looked into why your tires are getting wasted so soon, I'd question them on that. Have they given you any ideas as to why they are cracking, did they check for interference fit? They shouldn't crack either, not new tires. As far as I know the only way that happens is a car sitting stored, not moving, outside with a sunny climate.

 

Hi,

Most of what Jeff said is 100% correct. There is a big difference though in a 235/45R18 vs. the 235/40R18. Especially on this car, as there is not a lot of extra room. The difference between the sizes is about 1 inch in height depending on the tire.

There is an issues with "SOME" specific tires in a 235/40R18. Not all tires are exactly the same size, even though they are the same size. Some tires have a taller tread (more tread depth) or have a wider tread width than others. What tire are you using? I know the Goodyear Eagle F1 All-Season is one specific tire that will rub if using an OE wheel.

Also the OE wheel on a 04 Audi A6 2.7T S Line is actually 45mm. Do you have the OE wheels or aftermarket?

The first thing I would do is make sure you get that 235/40R18 on the car. This might solve your entire issue. If you have additional questions please let me know, I am happy to help.