My HF 212cc bike, with the Servi sheave will go 50mph with my 4" drive pulley but, the carb has been re-jetted, and the exhaust, and air intake, has been opened up. A Whizzer sheave, being smaller, would make it go faster, but the engine would need to work harder to do it unless the drive pulley was down sized. (3.5" or smaller), to compensate for the different ratio. The load, weight, rolling resistance, clutch set-up, etc., will also affect overall speed and performance. The TAV2 unit is a different high/low speed ratio than that of mine I'm sure.