Thanks for that explanation, William, that was enlightening, and jives with my experience. The way my non- engineer's brain makes sense of this is this:
The main brake cable moves up when you engage the brake. For a high profile canti to engage you also mostly need to pull up on the straddle wire, and inward a little. On a low profile canti, you mostly have to pull *in* on the straddle cable, while pulling up does very little good. So on a low profile canti the straddle cable has to change the direction of force from the main brake cable, and yes, that's easy to get wrong. On a high profile canti, the straddle cable serves merely as an extension of the brake cable transferring the brake force to both arms. It doesn't have to change the direction of the force, and is thus relatively immune to geometry. (I am sure this explanation won't satisfy an engineer, but it works for me) :) Gernot On Aug 30, 12:23 am, William <tapebu...@gmail.com> wrote: > Sheldon (RIP) did a great job of laying out the geometry factors, but didn't > really get to the punchline. > > The punchline, in my opinion is that the mechanical advantage of high > profile cantilevers is almost constant regardless of straddle cable length. > Brakes like Tektro CR720s and old Mafacs and similar, has a particular > mechanical advantage. You can adjust that a tiny bit, like a few percent, > by raising or lowering the straddle wire hanger, but you can't make a major > change, no matter where you put it. The upshot is, if you like how those > brakes feel with your lever, then be happy, because there is almost nothing > you can do to mess it up. If you don't like how they feel (probably because > of too little mechanical advantage), then you can tinker all day long with > straddle position, and it really won't do much. A different lever that > changes mechanical advantage might make a difference. A different brake pad > compound that doesn't need as much force to grab might make a difference, > but high profile cantilevers are not very tuneable. You'll see some folks > running their straddle right above the fender, and others several inches > higher. Those two setups won't feel a lot different, all else being equal. > The Riv-ish upside to this is that if you use high profile cantis with a > lever that works, you can raise the straddle high to clear your rack, > fender, and fat tire, and still get similar braking. > > Low profile cantilevers are super tuneable, but that give you more > opportunity to get it wrong. If you are forced to move the straddle to > clear a fender or rack, you may be disappointed at the major effect that had > on braking performance.. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
