17" wheels work
I have a set of 17" Enkei RS-6 wheels on my Explorer. I got Pirelli Scorpion Zeros in size 275/55. If you get the right size, you can get the same outside diameter, which means no need to correct your speedo. I believe that as long as the diameter is with in 0.1 to 0.2 inches it shouldn't make too much of a difference in speedo reading. My wheel/tire combo is only 0.1 inch larger and I can't see any difference. Also, make sure you get the right offset in your wheels. Some 17 inchers will have the tires rubbing on the front swaybar. Explorer Express has a set of spacers to eliminate this problem. They also sell 17" wheels.