DB22

Has anyone fitted 255 40 20 on the A6 C7 OEM wheels? Stock is 35 series.

tenspeed

I didn't think a 5% change would do much but I checked Custom rims, wheel tire packages for your ride - RIMSnTIRES.com and it shows a one inch increase in diameter.
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"Wheelwells clearance: Will fill out the wheelwell by extra 13 mm. Make sure that you have enough room under the fender. If not, consider lower profiles or smaller rims.

SPEEDOMETER: When speedometer reads 60mph (96.6km/h) actual speed will be 62.3mph (100.3km/h): 3.8% faster."

DB22

Thank you, I have also heard that some dealers will not mount anything but spec sizes. I figured that somebody on the forum may have tried it so I thought that I would enquire.

tenspeed

You're welcome. Dealers won't stray from OEM sizes. It eliminates problems.

I can't recall ever buying a tire from a dealer. I usually use OEM sizes on my cars unless there is a monetary gain. I spent $200 less for the A7 Continental DWS 06's by going 10 mm wider.

Baloo588

I did 275/35R20 on my A7 compared to 265/35R20 and my dealer was fine. I also did 255/45R20 on my A8 over the 265/40R20 which was fine.