Trying to figure out what will work for my C63S Coupe.

I'm ordering the 20/19 wheel combo but for Canadian winter driving I think a square setup would be best.

Usually step down from 19 to an 18" wheel with a fatter profile to match the rolling diameter. If I go with a square setup all around with 18s, I'm hoping I won't disturb any speed sensors as the backs will be a bit smaller than what was programmed at the factory with it expecting 20s in the rear.

Does anybody know the suggested winter wheel/tire size from the dealership on the C63S Sedan fitted with the summer 19s so I can start searching for wheels/tires? I'd like to order my own rather than get it through the dealership.

Also does anybody know what range of Offset/ET will work with the C63'S' and its brake package (non-carbon ceramic)? Same for Coupe/Sedan?

Dealership is unable to give me these figures as of yet. They say they need a VIN to figure it all out and I've seen some differing numbers online.

I'm hoping my Audi S5 winter rims/tires might work...45 ET, 245/45/18...a bit narrow for RWD and 516 lb-ft but might do for another season.

Thanks!