SCOTT PEDERSEN SUNTOUR SE from Sheldon Brown
: http://sheldonbrown.com/tandem-brakes.html
Self-Energizing Cantilevers
Because of the myth that conventional cantilevers aren't strong enough for tandem use, some people favor Self-Energizing cantilevers. These don't have a simple pivot, instead, each arm moves on a steep multi-start screw thread, so that as the shoe approaches the rim it also moves forward. When it rubs on the moving rim, the forward pull tends to increase the inward pressure, providing a "positive feedback."
This design can apply greater braking force for less finger force than a conventional cantilever, but it is difficult to modulate it. The original Scott Pedersen SE brakes were available either for front or rear use (opposite direction threadings), but when Sun Tour bought the design, their legal department vetoed the front version, so only the rear model was made by Sun Tour. I advise against the use of Self Energizing brakes, because they make it too easy to lock up the wheel.
Self-energizing Brakes http://sheldonbrown.com/gloss_sa-o.html#self
Self-energizing brakes use some of the braking force to provide a "power assist" to the brakes. The best-known self-energizing brake is the Scott-Peterson (
Sun Tour)
cantilever, which has a steep, helical thread as its pivot, so that the forward force exerted by the
rim against the pads helps cause the pads to press harder than they would from hand effort alone. Self-energizing brakes are quite controversial, because they can have a non-linear response, which may lead to wheel lock-up.