The existing tires are 33X9.5X15. I'm not looking for fast speed but would like to increase my top speed from 45-50 to around 55 if possible without running the engine at too high r.p.m. Can anyone tell me what is the tallest tire size i could mount on my existing rim; approximately how much taller that would be and finally approximately how much increase in mph i would gain with the tallest tire? Thanks for all your advice and help.