i got the 1.25 inch drive roller and it does well on the flats but not so good on hills probably because i weigh 260 pounds (and im not even fat!) top speed so far is 18.6 MPH on flats, its currently not working because the carburetor was giving the motor too much fuel flooding it out and the air/fuel screws didnt help, monsterscooterparts is gonna send me another carb for free!, they have the best customer service and ship fast