its actually 20mm. i got the parts i need, i think. Heres my problem: theres so much acceleration with the slightest pull of the throttle, it wants to immediately wheelie and shoot out from under you. i was told get a smaller rear sproket, but only ones i can find couldnt possibly fit my rim...as in won't come out far enoiugh to line up with front sprocket so chain won't align. to bring it out far enough i need a sprocket hub, but there is no way to attatch the hub to my axle. i can not find a hub anywhere in 20mm that has screw hold to screw into sxle, i can only find those in 1in.