#21
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More Brakes
On 13/12/15 18:08, wrote:
snip How do I post a picture? Is good enough for this. http://picpaste.com/Boat-DGqctqz9.jpg In the pictures you can see that the angle is a little long un-actuated. But the closer to full-on the closer to 90 degrees the angles get. So the change in angles isn't the problem since the harder you pull the better the leverage gets. Since the pads are stock I think that I'll try your advice and try a softer higher traction brake pad. |
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#23
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More Brakes
On 12/13/2015 11:45 AM, wrote:
On Friday, December 11, 2015 at 5:45:24 PM UTC-8, Frank Krygowski wrote: I suppose we could get into a technical discussion about what affects the performance of cantilever brakes. I'd say a prerequisite would be to read and understand Sheldon's article. Then be prepared for some equilibrium calculations - you know, free body diagrams, summing forces, summing moments, all that. Frank, in Sheldon's discussion of the U-brake it sort of hit a spot. As you apply the Cantilevers the angle between the actuation cable and the brake reduces thereby causing successively lower mechanical advantage. And that is what my problem felt like. V-brakes do not have this change in leverage. OK, if you have low profile cantilevers (those with arms that are nearly vertical), you'll see a change in mechanical advantage as the cable yoke pulls upward on the transverse cable. But almost all that motion happens when the brakes are merely moving the shoes through open air, essentially taking up slack; and that change in mechanical advantage doesn't matter much. One the brake shoes contact the rim, there's a lot less motion, and a lot less change in mechanical advantage. I suppose the change in cable angles that occurs between light brake shoe force to heavy brake shoe force (due to flexing of the rubber brake blocks, spreading of the cantilever bosses, bending in the cables, etc.) does decrease the mechanical advantage. And I guess this decrease in MA tends to make the brakes less linear in their action. IOW, if you applied your brakes, then wanted a 20% increase in braking force, you might have to apply 25% (a wild guess) more hand force. But I haven't found that to be a problem. I'll note that the classic wide profile cantilevers (here's a modern verson: http://www.ecovelo.info/images/neo-retro-1-485.jpg) had hardly any of that change the relevant angles. The distance the cable yoke moves up almost exactly matches the distance the end of the cantilever arm moves up. The shape of the straddle cable barely changes. Those wide profile brakes do have other disadvantages, though. The big one, in my book, is the clearance problem. For example, they tend to interfere with my rear panniers. Because of that, I use low profile cantis even on our tandem. Set up with a fairly short transverse cable, they are very powerful. -- - Frank Krygowski |
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