Glixal ATKS-03902 Chinese Scooter High Performance Racing Torque Spring clutch springs GY6 50cc-100cc 139QMB Engine Moped ATV (1500RPM,Yellow) Yellow Color,1500RPM, 3pcs of Clutch Springs & 1 Torque Spring The lowest rated 1K Springs may give you a higher speed overall but will engage at a lower RPM on take-off. Hard to "climb the hill" The 2K Springs will give you the greatest grabbing power and a higher RPM at take-off.Easy to "Climb the hills" but may be slower in speed overall The 1.5K springs have the balanced performance. Please Note: The exact performance of upgrade parts will be affected by many other factors