Dr. Pulley 23x18 Sliding Roller Weights Dr. Pulley 23x18 Sliding Roller Weights for 250cc water-cooled 172mm engines. Select weights on sale; 10g and 12g.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 ramp to change the gear ratio. This unique sliding movement (not rolling) provides exclusive advantages to increase CVT perfor mance. With Dr. Pulley, no abnormal wear will occur even when running in high gear.Please see our Warranty & Returns Policy. Size: 23x18 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