====================================================================== From: vschuck@zippy.sonoma.EDU Date: Wed, 18 Nov 92 11:28:14 PST Subject: SE Brake Joys >Vern, > >Can you explain how the self-energizing brake works? I assume it's a >caliper brake? > > Thanks, Ben (Carnegie Mellon University, Pittsburgh) ------------------------------------------------ I just knew someone would ask that question :-( Here is goes . . . Todays SCOTT SE design looks like, and replaces, the modern cantilever brakes found on ATB/MTB's, not calipers. What I put on my TEasy replaces their predecessor to the cantilever, the SHIMANO U-BRAKE and SAKAE ROLLER-CAM. But the SE feature works the same on both designs. (These two old designs were solutions to the problem of how to reach the rim while going around a big nobby tire.) Each half of the brake does not pivot about the cantilever braze-on. (A std cantilever pivots on the braze-on.) Each half of the SE mechanism is tight to the frame and doesn't move. The SE has its own internal pivot or bearing surface, but it's not a smooth bearing surface. The internal surface is a helix. As each SE pivots it also moves "downstream" with respect to the wheel rotation; ie, it moves on two axis at once. When the pads engage the rim, some of the energy stored in the wheels rotation is used to further engage the pads. That is positive feed back. But, because it is slowing the wheels rotation, energy available as the wheel slows is decreasing, thus reducing the amount of feedback. The designed balance between the gain offered by the helix and the decreasing energy available must be such as to never cause a lockup situation . . . I hope. > Eric says . . . >Nasbar sells the Scott SE cantilever Brakes ("uses the forward momentum >of the rim to self tighten ...") at $41.95 (Catalog #83 summer 1992). I >think that normal canti's would work very well. Yes, they do work very well. But they can't perform well when you have a LONG cable, especially a cable in a lot of housing. My TEasy housing/free air route is about 50/50. The SE permits a minimum of hand effort for a high degree of brake force. This is important in sustained braking, like those long downhills that I so often find on my MTB. Oh the hand cramps! yech! :-( ------------------------------------------------ - @ - _ \ _ "Happy Trails" -- (*)-^+-(*) "Recumbency. It makes life worth living." ------------------------------------------------ Vern Schuck vschuck@zippy.sonoma.edu Sonoma State University, Rohnert Park, CA 94928 ------------------------------------------------