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Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 6:25pm
by nirakaro
I'm reading Sheldon Brown on the geometry of cantilever brakes, and can't make sense of it.
Specifically, he says that the shorter the yoke cable, the greater the MA. And conversely, the least MA will, in theory, come from an infinitely long yoke cable. But as I visualize it, pulling up on a very short yoke cable will move the brake pad a lot for a small pull, which, unless I'm misunderstanding the terminology, is a smaller MA. And as you lengthen the yoke cable, you need a longer pull to get the same movement of the brake pad. And with an infinitely long yoke cable, it would take an infinite pull on the brake lever to move the brake block at all. Which is an infinite MA, no?
What am I misunderstanding here?

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 6:31pm
by landsurfer
Had really nasty squealing with the original cable set up on my Jamis Canti brakes .... i read Sheldon's article, bought some bits from SJS ... Shorter Cable = No Squealing !

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 6:46pm
by rjb
Plough through this discussion viewtopic.php?f=5&t=57410

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 7:01pm
by jb
The nearer the straddle wire is to a straight line the more force is transmitted to the cantilevers, you will find if you look carefully that the movement of the block is actually a lot less than the vertical movement of the wire.

An infinitely long wire on the other hand, will pull the cantilever straight up whilst transmitting virtually nothing to the movement of the block

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 8:16pm
by cycleruk
nirakaro wrote:I'm reading Sheldon Brown on the geometry of cantilever brakes, and can't make sense of it.
Specifically, he says that the shorter the yoke cable, the greater the MA. And conversely, the least MA will, in theory, come from an infinitely long yoke cable. But as I visualize it, pulling up on a very short yoke cable will move the brake pad a lot for a small pull, which, unless I'm misunderstanding the terminology, is a smaller MA. And as you lengthen the yoke cable, you need a longer pull to get the same movement of the brake pad. And with an infinitely long yoke cable, it would take an infinite pull on the brake lever to move the brake block at all. Which is an infinite MA, no?
What am I misunderstanding here?

In my mind a short yoke cable will give a greater force on the pads than a longer one for any given force on the brake lever.
So therefore has more of a mechanical advantage. :roll:

My set-up to give best braking =

In theory the angle between the red and blue lines should be about 90 degrees when the pad hits the rim.
Oryx copy.jpg

In practice.

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 9:37pm
by 531colin
rjb wrote:Plough through this discussion viewtopic.php?f=5&t=57410

^^^^^^^ Wot E said!!

Re: Mechanical advantage is doing my head in!

Posted: 6 Jan 2019, 10:37pm
by NATURAL ANKLING

Re: Mechanical advantage is doing my head in!

Posted: 7 Jan 2019, 8:54am
by Chris Jeggo
531colin wrote:
rjb wrote:Plough through this discussion viewtopic.php?f=5&t=57410

^^^^^^^ Wot E said!!

^^ Wot they said!