Bigger tires may give you a higher top speed, if you have a gps. My old AC 500 hit 64 mph gps with 30" Mudzillas, now with 25" Dunlops, it struggles to get to 55. I can't see it's much quicker, either. My AC Diesel, however loves the 30' Mudzillas, 49 mph! Was only 41 on the 25's.