Dr. Pulley 21x17 Sliding Roller Weights Dr. Pulley 21x17 Sliding Roller Weights for the Aprilia Atlantic 200/250 and Scarabeo, Piaggio Beverly 200/250, Liberty 200, X8 200, X9 200 and X9 250 Evolution, Vespa GT, GTS, GTV 250/300 and many more. Select weights on sale; 8g and 15g.Please select weight from drop-down menu. Traditionally, gear ratio is changed by the up-and-down rolling movement of the roller weights in the ramp of the Moveable Drive Pulley (MDF). Now the innovative Dr. Pulley Sliding Roller Weights slide up-and-down the r amp to change the gear ratio. This unique sliding movement (not rolling) provides exclusive advantages to increase CVT performance. With Dr. Pulley, no abnormal wear will occur even when running in high gear.Please see our Warranty & Returns Policy. Size: 21x17 Set of 6 Broadens your range of gear ratios Increases acceleration and re-acceleration properties Increases top end speed Lasts longer than standard roller weights U.S. Patent Number: 7,276,004 Select weights on sale; 8g and 15g.