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Old 11-17-11, 05:29 PM   #1
mikemowbz 
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brake reach, pad position and optimum braking power

I've been wondering lately about how reach & pad position relate to braking power, and wondering if someone could fill me in on how this works, and what's optimum for the best possible performance. It probably doesn't make a huge difference, but I'm curious - and it's a bit of a technical question, so I thought I'd take it to the mechanics.

To give a concrete context, my new setup (involving a number of new parts on a 1985 Nishiki Prestige) includes a set of mid-reach (47-57mm) brakes, Shimano B650(?)s; I was told that the old Suntour Cyclone calipers that came off the frame and forks I started out with ran 47-57mm, so that's what I got. Turns out that short reach would have worked...better. With 700c rims, the mid-reach brakes need the pads to be set up right at the very top of the slots, and the little bolt on top slightly relaxed (these are new dual-pivot brakes), to get a good position. Obviously, 39-49mm brakes would be down near, but not quite at the lower end of the slots. I feel like that would give more leverage, and thus closer to optimum braking performance. Does this make sense?

Down the line, if I can find a use for the mid-reach calipers elsewhere, would it be worth my while to swap them out for short-reach? If anyone is particularly knowledgeable, I'm kind of interested in the physics/mechanics of this as well as the practical side...
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Old 11-17-11, 06:11 PM   #2
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leverage and cantilever. if the pads are in the same position, the leverage does not change, provided that the opposite cable side have the same dimentions.

easiest way to describe it is a seesaw.
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Old 11-17-11, 06:19 PM   #3
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Read Sheldon Brown's article on rim brakes (http://sheldonbrown.com/rim-brakes.html). I don't recall him discussing mechanical advantage with respect to caliper brakes, but he discusses it in depth in context of cantilever brakes. To be honest I don't think it will make a bit of difference. I think that the pads, cable friction and braking surface will be the most significant factors.

Are you having issues braking?
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Old 11-17-11, 06:34 PM   #4
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Naw, it's really not a functional problem. I think it's fine, ultimately. I'm just curious whether it's remotely significant.

The one thing I'm not 100% on, aside from the technical question about optimum performance vis-a-vis position, is that the mechanic who set up the bike said she'd had to loosen the little screw on the top of the of the middle section of the caliper (this is the part that includes both the right caliper arm - if you're looking at the front brake from a riding position - and the section that runs up to the barrel adjuster...it's on the left, just above the other arm). This appears to leave the whole assembly a little bit loose, if I'm not mistaken. Not sure exactly how this helps, but...

I'm certainly happy (and safe) to leave it as is more or less indefinitely, but wanted to know if you folks thought it would make any difference if I eventually felt like switching them out for short-reach...if there would be any advantage at all.

Thanks for the responses!
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Old 11-18-11, 12:33 PM   #5
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the mini screw on the top is for adjusting the arms left or right. It's there so that both pads hit the rim at the same time.
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Old 11-18-11, 12:52 PM   #6
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There is an adjustment slot for brake pad height, you may have the option
of top of the slot, longer reach, or bottom of the slot, shorter reach.

design balance : stiffer, more grams of metal, vs, lighter and a bit less rigid.
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