Just took delivery of my 70D last week and am looking to use the OEM 19" wheels for dedicated snow tires (Michelin X-ice) and get some 20" wheels for summer driving with dedicated high performance summer tires. The 20" choice is a compromise of driving performance, appearance, and durability with the awful Chicago roads over the 21" set up. My question is that there is a really limited supply of 20" high performance, XL load rated tires that will exactly duplicate the overall wheel/tire diameter of the 19" OEMs. I think Continental and Bridgestone might have a 245/40/20 in a high performance summer tire. Does anyone know how the AWD will react if the diameter of the wheel/tire is slightly larger?