FORGOTTEN MOTOCROSS TECH: THE SUSPENSION IDEA THAT USED THE BRAKE PEDAL
Motocross history is filled with examples of creative ideas that were heralded as groundbreaking, but, because of the rapid rate of change in development, sank into the swamp of forgotten technology. Although some are best left abandoned, others were truly innovative (if not ultimately successful). MXA loves to reveal motocross’ tech trivia. Do you remember this idea? Do you remember Yamaha’s Brake Activated Suspension System?
BASS was designed by Yamaha’s engineers for the 1985 model year, BASS was the Yamaha acronym for “Brake Actuated Suspension System.” The idea had some merit on paper, but it didn’t work on the track. A cable ran from the rear brake pedal to the shock’s compression valving. When the rear brake pedal was pressed, the cable would open a valve to lighten compression damping. Typically, when you applied the rear brakes in choppy bumps, the torque effect between the wheel, swingarm, chain and shock stiffened the rear suspension‚ causing wheel hop.
By opening a valve when the rear brake pedal was pressed, the shock damping was free to absorb braking bumps and lessen “Yamahop.” The damping change was 12 percent (the equivalent of six clicks out on the compression adjuster). BASS wasn’t a failure through braking bumps, but, unfortunately, BASS worked anytime the rear brake pedal was pressed and would lighten the shock’s damping on the face of jumps, in smooth corners, and when dragging the brakes through whoops.
However, the torque effect problem could not be solved by slightly lighter compression damping. Later, ATK’s Horst Leitner and Eyvind Boyesen developed anti-torque rear suspension systems that solved the chain torque problem without utilizing the shock.
The cable attached to the rear brake pedal is routed to the top of the shock. It has inline cable adjusters for tension settings.
BASS was not a hit with MXA test riders. We would either cut the cable or wire it open (and install a stiffer shock spring). In most cases we sent the shock out to have it revalved by the White Brothers (and have BASS removed). Yamaha dropped it one year later. It was discontinued in 1986.