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Old 02-21-07, 04:36 PM   #1
Phantoj
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Brake feel and performance...

Allow me to present a very short dissertation on brake feel and performance:

There are three variables involved.
  1. Lever force
  2. Lever travel
  3. Braking force

The ideal brake would perform as follows: Braking force would be linearly proportional to lever force and would reach the maximum needed (enough to flip the bike or slip the tire on dry pavement) with a reasonable force on the lever. Lever travel would be zero.

In this ideal brake system, braking force would be totally independant of any other variables, such as time, weather or how hot the disc/rim was or whatever.




My sidepull calipers are pretty good in the dry, they deliver all the stopping power I need with a reasonable amount of force on the lever and not much lever travel. In the wet, they are much less linear, and the braking force is also related to time spent squeezing the lever - after the pads clear the rims, they work better.

My mechanical road discs perform well, wet or dry, with one weakness - too much travel. I can still get all the braking power I need, with much less lever force, but the lever moves almost to the bars. The relationship between lever force and stopping power seems more linear -- I think this makes them "easy to modulate".

Thoughts, comments...?
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Old 02-21-07, 06:14 PM   #2
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I like the solid feel of V-levers on standard cantis at the cost of slight decrease in stoppong power.
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Old 02-21-07, 06:14 PM   #3
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Quote:
Originally Posted by The Fixer
I like the feel of V-levers on standard cantis at the cost of slight decrease in stoppong power.
How is the feel better? I haven't ridden V-brakes in ages.
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Old 02-21-07, 06:15 PM   #4
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Quote:
Originally Posted by Phantoj
How is the feel better? I haven't ridden V-brakes in ages.
Solid action, no mushiness...
I'm talking V-brake levers used with non V-brakes, either cantis or calipers
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Old 02-21-07, 07:24 PM   #5
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http://sheldonbrown.com/canti-trad.html#ma

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Old 02-21-07, 09:49 PM   #6
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Sounds to me like the rotor is not running true to the pads and the pads are set too far from the rotor so they don't scrape. Therefore you have to pull in more cable to get complete contact. Or your cable is tired out ?

I have Avid BB 7's and you leave the caliper loose to the frame mounts, then adjust each pad hard to the rotor before tightening the caliper to the frame. When the rotor has almost no runout relitive to the pads, they can be kept very close to the rotor surface. Read your manual and go through the adjustment procedure.

Hope thats not too long.

:-)
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Old 02-22-07, 05:02 PM   #7
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Originally Posted by jtfind
Sounds to me like the rotor is not running true to the pads and the pads are set too far from the rotor so they don't scrape. Therefore you have to pull in more cable to get complete contact. Or your cable is tired out ?

I have Avid BB 7's and you leave the caliper loose to the frame mounts, then adjust each pad hard to the rotor before tightening the caliper to the frame. When the rotor has almost no runout relitive to the pads, they can be kept very close to the rotor surface. Read your manual and go through the adjustment procedure.

Hope thats not too long.

:-)
I think the problem I had was that my brakes (Avid road disc) were set up badly and the bike was run that way before I got it. So, the pads were worn unevenly. I replaced pads and re-setup the front brake, and it works pretty good. The rear I didn't bother with, and it's not too good, but it's adequate.

I have seen similar comments about Avid road discs in the commuting forum - users not pleased with the amount of lever travel. With my current front setup, I can get sufficient braking force for my rather extreme needs (I bomb down a big hill every day, in all weather), but the amount of travel at the lever is still more than I think is good. These brakes would be better if the mechanical advantage was lower - a harder pull required to stop, but less likely to bottom out the lever.

I think the extra lever travel is related to them being designed for the shorter pull of road brake levers. With a shorter pull, the tension in the cable for a given amount of squeeze on the lever is higher, resulting in more "flex" in the system. Also, the shorter pull means that the effect of any slight flex in the system is amplified in the amount of extra lever travel it creates - a double whammy.

Shimano recently released a road disc brake. I wish they had released a "V-lever" STI instead. Maybe they're waiting to release an STI with integrated hydraulic brake...
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