1956  Rim Clutches

Sometime called a shoe clutch, this first-generation kart clutch was noted for its simplicity and consequential low cost.  The friction material had a curved shape that rubbed against a drum.  In the late 1970’s springs were added to improve acceleration characteristics but the rim clutch still suffered from rapidly changing temperature gradients that caused irregular engagement speeds.

1978  Disc Clutches

Gilbert Horstman introduced the second-generation kart clutches which included a flat friction surface that minimized temperature variations and allowed the clutch engagement speed to be much more predictable.  It was mechanically more complex and subsequently more costly.

1995  Soft-start Disc Clutches

Third-generation kart clutches connect springs directly to the levers.  There is no pressure plate.  This simplified clamping mechanism engages the engine without “bogging”.  Patented in 1995, 2001, 2003 and 2015 by Thomas Fehring.