Clutch Works

The Next Step:
Many modifications can be made to the clutch assembly to increase efficiency and performance. Introducing stiffer springs or changing the friction pad compound can greatly increase the amount of torque that the clutch can handle.

SSB headed down to Barnett Performance Products for a factory tour with Xavier Romero, production manager for the 60-year-old company.

Xavier clued us in on the intricacies of the modern clutch and reinforced the idea that altering a stock bike's power and/or drivetrain changes the requirements on the clutch-generally resulting in the need for heavy-duty components.

OEMs design the stock clutch system for the level of power that the bike produces in stock form. Power adders like nitrous, turbos, big-bore kits and superchargers typically make more torque than the stock clutches can handle. In addition, the resistance of the transmission increases when a stretched swingarm and wide-tire kit are installed. In both cases stronger clutches are a must.

In hard riding applications like road racing and serious canyon carving, banging hard downshifts while jamming on the brakes can cause the rear wheel to lock up as the clutch grabs abruptly with the large change in engine rpm. Modern slipper clutches utilize a cam system, and in some cases sophisticated electronics, to allow the clutch to engage more slowly under these harsh conditions.

The science behind these things gets pretty hairy when engineers begin to consider manifold pressures, mass air velocities in the intake tract, relative angles of rotation between the output shaft, clutch basket and carrier and the rear wheel. But rest assured the geniuses that develop these parts have got it on lock. The latest and greatest slipper clutches keep that rear end spinning smoothly under even the harshest downshifts.

Xavier reminded us that, "Even after 60 years of evolution there is still much to be learned about clutches that will make them perform better and last longer."