Right now I have 22" rims with the goodyear fortera SL tires. Would switching to a smaller rim 17/18" and say some BF goodrich A/T affect performance and mileage negatively or no affect or better affect?
If your tire height stays the same,it shouldn't make any difference. For example, a 33" tall tire on a 22" rim should be close to the same height as a 33" tire on a 17/18" rim. You'll just have more sidewall. Ride and handling will probably change more than performance and mileage.