[plkracer]

My uncles raptor did 81 before it hit the rev limiter in last gear (this was with the wind at sand lake), so if you want it to hit 55, with the same 20 inch tires, I'd say a 65 tooth sprocket. A 60 would be reasonable too. You could always gear the front down. I think it uses a 15 tooth front, so if you went to 13, you could drop the rear to a 52-55. With 22's, I'd go a 13 front and 60 rear.