never seen 20's but with an appropriate tire size so the overall hight is the same as stock, i dont see why a bigger wheel would be an issue. i do get a slight rub if i hit a pothole hard enough but it takes a lot. i also noticed that with my buddies GXP that when the rear squats down hard (lots of weight in the trunk) that the wheels tend to camber in so i dont think that you would have issues with rubbing especially if you could keep the offset around 45mm. my 38mm offset has a good inch of clearance to the strut so there is room to tuck them in a bit more or go to a 9 inch wheel. i can run up to 265 rubber without an issue. with a 20 and the shorter sidewall on the tire probably only be able to run a 245 or 255 without issue on an 8.5 inch rim.