Need help with choosing proper size winter tire and wheel set for S7

[NPKR]

I have never had dedicated winter and summer tires/wheels before, always had A/S. I am now searching for a winter wheel and tire set for my new S7, to be arriving at my dealer later this month, but I have never bought and paired new wheels with tires.

I would really appreciate it if some of you guys would help me with understanding how this works, really a couple of specific questions:

While searching on Tirerack, I searched for available tire/wheel pkgs for an S7. The 255/40/19 tires (OEM rec size) I selected are paired by Tirerack with wheels that are 19 x 8.5 inches. But the calculated width of the tire is 255mm divided by 25.4mm/inch = 10.04 inches. How does a 10 inch wide tire fit on an 8.5 inch wide wheel? Am I missing something? Are tires usually wider than the wheels they are fitted to?

Any specific recommendations? I live in Massachusetts so snowfall is significant although not severe compared to some areas. I'm thinking of trying a tire with slightly taller sidewalls for pothole protection and a bit narrower tire for better traction in snow. So, is there any problem with going to a 245/45/19 tire instead for the reasons indicated? Should they fit/clear the S7 wheelwell? The total overall diameter of this wheel/tire combination I calculated to be 27.68 inches, which is slightly larger than the 27.03 inches for the OEM recommended (255/40/19) winter wheels/tires and the 27.30" for the OEM rec (265/35/20) summer wheels/tires.

If it is OK and advisable to use 245/45/19 tires on an S7, what size 19 inch wheel should be paired with them? Would it still be 19 x 8.5 or would it be narrower (ie, 19 x 8) to accommodate the slightly narrower tire?

Thank you

[Luis_Heineken]

just check the tire size that you are using or check the driver door or the door post, you will find the tire size recommended by Audi

[MacFady]

This can show you (http://1010tires.com/Tools/Tire-Size-Calculator) how different sizes compare to one another in things like rolling radius etc. You will be fine with all you mentioned, you can put a 245 on a 8.5 or an 8.0, but a 19x8 wheel is a lot less common than a 19.8.5. 255 is also fine on what you mentioned, and 8.5, despite your calculations it wont be bulging over the wheel. I'll just mention, since you did, that a 245/45 is only going to give you 8mm more sidewall than the 255/40.

[NPKR]

MacFady, Thanks for that link- very helpful.

Could some members tell me the size of the winter or summer tires and wheel rim width they are using on their S7 with 19 inch wheels? Anyone using 235 or 225 width tires for winter duty on S7?