[Bob wrote: However, the end of the caliper arm is moving up]
The cable connecting ends of the brake arms aren't moving up relative to one another, they are moving toward each other. Therefore the original example is correct as written. The shorter the cable, the more braking power you have. With a long cable you lose the lever advantage.
If you had only one side doing the braking, your "stake through the trunk" analogy would be correct, but you have two brake arms. The idea is that braking moves the cable-attached ends toward each other is an "arc-ed" or pivoted, yet still effectively a straight line relative to one another.
I humbly submit the above, acknowledging that I'm not above err.
Steve Dahlquist Velochrome Frameset Painting V 559-592-6367 F 559-592-2585 C 559-967-3318 steve@velochrome.com 22582 Carson Avenue Exeter, California 93221 http://www.Velochrome.com
----- Original Message ----- From: BobHoveyGa@aol.com To: classicrendezvous@bikelist.org Sent: Friday, April 16, 2004 10:12 AM Subject: Re: [CR]Center Pull Staddle cable question
Steve wrote:
>With a longer straddle cable, you get LESS brake power. > You are applying brakes inwardly, not upwardly,
Just the opposite... with a longer straddle cable you get more braking power (i.e., more mechanical advantage) but longer lever travel per given movement of the brake pad.
You are right, the pads are indeed moving in. However, the end of the caliper arm is moving up, and that's what matters since that is where the cable is attached. Shortening the cable brings the direction of pull more in line with the arm, thus it takes a harder pull to get the lever to move up (but also a shorter pull... the lever will operate the brake faster but with less power).
>Similarly, if you have a rope stretched between two cars in neutral, and you pull on the rope, they will move toward each other. But, when you have pulled them together and the rope is pulled far from the cars forming a "V", they will not so readily continue to move toward each other, momentum notwithstanding.
Not a very good analogy, since the cars are rolling along a straight line axis. Brake arms are not, they are rotating around a pivot. Assume your cars are facing each other and the cables you're tugging with are attached to the front bumpers... now before you tug the cables, drive a giant stake thru the trunk of each car into the ground, then see what happens when you stand between the cars and pull on the cables... not a thing. But stand at a right angle to the cars and the front of both cars will move towards you, pivoting on their respective stakes).
Bob Hovey Columbus, GA
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