Originally Posted by
AnthonyG
Actually I'm sure you could get even more power out of a v-brake if you used a standard pull lever and NOT a v-brake specific lever. The drawback is that you will have minimal pad to rim clearance to get it to work and NO tolerance for any rim that is even slightly out of true or pads that don't want to centre reliably.
Now I'm sure that what your doing with a low profile cantilever setup is making the cross cable so short that it effectively pulls as sideways as possible, just like a v-brake and since you are using low cable pull levers you have good mechanical advantage but you also have all the issues of close clearances with no tolerance for any out of true wheels or non centering pads.
In the real world v-brakes offer you the best of all worlds with no fussy issues to sort out.
Anthony
You are correct in your description of the setup, but not why it provides stopping power... if you consider a set of low-profile canti brakes with a very short straddle cable - for argument's sake lets say it is so short it goes straight across. To actuate the brake you pull up at the middle of the straddle cable. After the pads hit the rim we can consider the brakes as a static system - all forces balance each other out. the tension in the cable pulling up at the middle of the straddle is a certain amount, lets call it 't', and each side of the straddle cable must hold approx. 1/2 of that, or 't'/2. BUT the centre cable is pulling straight up and the straddle cable is pulling at a very shallow angle with almost no vertical component at all, so the tension in the sides of the straddle cable have to be much much much higher than just 't'/2... 't'/2 is just the vertical component of the force the straddle applies to the brake arm and there is the larger horizontal component (larger because the low straddle cable is much more horizontal than vertical).
The actual amount of tension in the straddle cable is:
t/(2 X Sine A) where A is the angle between the straddle cable and horizontal... As A approaches zero (horizontal),
Sine A gets extremely close to zero, and a non zero number, 't' divided by a number approaching zero
approaches infinity...
For example, if the straddle cable is at 30 degrees, with cable tension of 10 lbs: 10lbs/(2 X Sine 30) =
10 lbs cable tension in the straddle cable. If A is decreased to 10 degrees 10lbs/(2 X Sine 10) =
28.8 lbs. at 5 degrees the tension is 57.4 lbs, at one degree the tension is 286.5 lbs...
If you pull the brake cable on a V brake with 10 lbs tension, the brake sees 10 lbs tension - no more and no less.
The problem, as you said, is that it gets increasingly hard to set up a brake with a very low straddle cable, including tire or fender clearance and rim run-out clearance. Also, the more you pull the cable the higher the straddle angle gets and the less this trigonometric leverage effect works for you. But it is not difficult at all to set up a low-profile canti with significantly
more power than a V brake.