The stiffer the spring, the later the clutch will engage allowing the engine to spool up to a higher RPM range before the clutch comes on. The later the clutch engages, the more the clutch will slip causing the clutch shoes to wear out more quickly.

MUGC0751 - 0.9mm - With these softer clutch springs the engine will engage earlier, which can be useful if the traction is very low.

MUGE0717A - 0.95mm -

MUGC0708A -1.0mm (black) - This is a set of stock 1.0mm clutch springs. This is the most common clutch spring for the Mugen buggies.

MUGC0753A - 1.1mm - If you need more bottom end from your engine, consider using 1.1mm springs with the aluminum shoes.