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  1. #1
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    Cantilever brakes with fork-mounted cable stop on carbon fork?

    I'm building up a bike with a carbon fork (the Nashbar CX carbon fork), and I'm wondering if the plan I have to use a fork-mounted cable stop with the cantilever brakes will work. I usually see on carbon forks some kind of non-cantilever brakes, or cantis with a stem-mounted stop. Specifically, I'm afraid that the brake bridge hole won't be able to hold up to the compression that the bolt will put on it. Should I be worried? If so, is there an alternate solution for cross brakes that puts the stop down low for better routing/performance?

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    What kind of stop do you plan on using? One of these (http://www.universalcycles.com/shopp...&category=1613) or something different?

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    coprolite fietsbob's Avatar
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    Not sure if there is always a fork crown hole in CF forks,
    doesn't need one for caliper brakes if there are mounts of a different type of brake.
    ie , V or disc.


    Threadless headset? some come equipped with a cable housing hanger designed in.
    http://www.universalcycles.com/shopp...5&category=726


    On the rear you can adapt one of these
    http://www.universalcycles.com/shopp...4&category=167

    or there are housing stop hangers that hang off the bolt, that holds your seatpost.
    http://www.universalcycles.com/shopp...388&category=7
    Last edited by fietsbob; 08-24-11 at 08:47 AM.

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    Senior Member Shimagnolo's Avatar
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    AFAIK, there are only two fork-crown-mounted cable stops:

    http://www.specialized.com/us/en/bc/...jsp?spid=47409
    http://www.amazon.com/Tektro-Brake-H.../dp/B000C14HNS

    I learned the hard way (200+ lbs, and 14% grades) that you don't want the cable stop mounted above the head tube.

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    why not run a disc brake on that fork?

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    Quote Originally Posted by Shimagnolo View Post
    AFAIK, there are only two fork-crown-mounted cable stops:

    http://www.specialized.com/us/en/bc/...jsp?spid=47409
    http://www.amazon.com/Tektro-Brake-H.../dp/B000C14HNS

    I learned the hard way (200+ lbs, and 14% grades) that you don't want the cable stop mounted above the head tube.
    I have that Tektro. I've found that mounting the stop higher (even on the steer tube) with the extra cross levers makes for bad cable routing. The stop mounted on the fork on my older bike works great. I can't imagine a headset mounted stop would work well at all, sadly enough. Just too tight of a curve for the cable.

    As to why don't I run a disc brake? I have cantis. They work. If I need to change 'em I will, but so far I don't have a problem with them.

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    Use the fork mounted stop. The hole in the fork could be used to mount a side-pull brake if you can find one with the right reach so it will take the load of the cable housing with no problem. I have very light all-carbon forks on three road bikes with sidepull brakes and these forks are certainly no stronger than your CX fork.

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    Senior Member Shimagnolo's Avatar
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    The problem with the cable mount at the stem is that the cable and the fork work like a string and an archery bow. When the brakes start to take hold, they flex the fork/steerer, rapidly increasing the force on the cable. What you have is a front brake that is either off, or locked on; No modulation whatsoever. Not fun descending Flagstaff Mtn with only the rear brake, because the front brake will lock up as soon as you touch it.

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    Quote Originally Posted by Shimagnolo View Post
    The problem with the cable mount at the stem is that the cable and the fork work like a string and an archery bow. When the brakes start to take hold, they flex the fork/steerer, rapidly increasing the force on the cable. What you have is a front brake that is either off, or locked on; No modulation whatsoever. Not fun descending Flagstaff Mtn with only the rear brake, because the front brake will lock up as soon as you touch it.
    That's overstating the case for most situations. I assume you have a 1" carbon steerer on a large frame which would magnify the problem.

    Headset mounted cable stops can cause shuddering and vibration particularly with carbon steerer forks but with the 1-1/8" steel steerer and fork, on my Surly Cross Check I have no problems at all with the housing stop located right under the stem.

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    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by HillRider View Post
    That's overstating the case for most situations. I assume you have a 1" carbon steerer on a large frame which would magnify the problem.

    Headset mounted cable stops can cause shuddering and vibration particularly with carbon steerer forks but with the 1-1/8" steel steerer and fork, on my Surly Cross Check I have no problems at all with the housing stop located right under the stem.
    Steel 1-1/8" steerer on large frame.
    Me + bike = 210 pounds.
    Grades up to 14% on Flagstaff.
    I generally saw the problem on grades >= 9%.

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    Wouldn't the braking action reduce the tension on the cable? It seems to me that the head tube would be pushing against the steer tube in a way to bend the steer tube forward, not backwards.

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    Praxis, I wouldn't worry about using that hole for a cable stop, just use the torque value for caliper brake mounting. I also have the Tektro unit on my touring bike, but only because I didn't know about the Specialized unit at the time. I had to drill out the Tektro to adapt it for the barrel adjuster.

    Brad

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    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by Iowegian View Post
    Wouldn't the braking action reduce the tension on the cable? It seems to me that the head tube would be pushing against the steer tube in a way to bend the steer tube forward, not backwards.
    If you are applying the brakes while rolling backward, then yes.

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    Quote Originally Posted by Shimagnolo View Post
    Steel 1-1/8" steerer on large frame.
    Me + bike = 210 pounds.
    Grades up to 14% on Flagstaff.
    I generally saw the problem on grades >= 9%.
    I'm surprised you have that serious a problem with a 1-1/8" steel steerer. I wonder if the housing stop is flimsy and flexy. Mine is a Tektro and is quite rigid.

    As to downhills, around me 9% is common and 14% is nothing special. We have >20% lots of places and mine never shudders or lacks control.

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    Quote Originally Posted by Praxis View Post
    .....Specifically, I'm afraid that the brake bridge hole won't be able to hold up to the compression that the bolt will put on it. Should I be worried? .....
    Short answer no. The cable stress imparted to the fork through the cable stop is miniscule compared to the overall stresses at the crown. If the stress imparted this way is worrisome, you have far more worries about the overall strength of this fork, especially for cyclocross.

    The crown area is far and away the strongest part of the fork, with deep reserves of strength because of it's critical nature, so mount the brake hole fulcrum and don't sweat what doesn't matter.
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    coprolite fietsbob's Avatar
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    Is there a hole in the crown of the fork you have? Praxis? ..
    If not then go with V brakes.

  17. #17
    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by HillRider View Post
    I'm surprised you have that serious a problem with a 1-1/8" steel steerer. I wonder if the housing stop is flimsy and flexy. Mine is a Tektro and is quite rigid.

    As to downhills, around me 9% is common and 14% is nothing special. We have >20% lots of places and mine never shudders or lacks control.
    The housing stop was a Problem Solvers. Quite solid.
    The flex was in the fork.
    Changed to a fork-crown mounted cable stop, and the problem is gone.

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    Quote Originally Posted by Shimagnolo View Post
    The flex was in the fork. Changed to a fork-crown mounted cable stop, and the problem is gone.
    That usually solves the problem. My Cross Check has never had the problem but I did buy a Tektro fork crown mounted stop as a precaution. Unfortunately the crown race stick out too far and the stop won't clear it so it sits in the parts box unused.

  19. #19
    Senior Member Shimagnolo's Avatar
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    Quote Originally Posted by HillRider View Post
    That usually solves the problem. My Cross Check has never had the problem but I did buy a Tektro fork crown mounted stop as a precaution. Unfortunately the crown race stick out too far and the stop won't clear it so it sits in the parts box unused.
    I'm using the Tektro.
    It required a sandwich of two star-lock-washers with a flat washer in between to clear the crown race.
    IIRC, I think I had to also grind the back of the Tektro flat.

  20. #20
    coprolite fietsbob's Avatar
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    I think I had to also grind the back of the Tektro flat.
    BAD.. you file aluminum, never use a bench grinder on aluminum.

  21. #21
    Senior Member vredstein's Avatar
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    Quote Originally Posted by Iowegian View Post
    Wouldn't the braking action reduce the tension on the cable? It seems to me that the head tube would be pushing against the steer tube in a way to bend the steer tube forward, not backwards.
    There's a long list of components involved in braking that flex way before the steer tube could ever get involved. The brake levers, housing, housing stops, brake arms, pads, cantilever posts, fork legs, and finally the rim wall itself.
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    Quote Originally Posted by Iowegian View Post
    Wouldn't the braking action reduce the tension on the cable? It seems to me that the head tube would be pushing against the steer tube in a way to bend the steer tube forward, not backwards.
    Yes. According to the theory, that is the problem. As you apply the brakes slightly, the flex increases the braking pressure until it hits reaches a critical point, or a zone of less friction on the rim, whereupon the brake slips and the system springs back ready to start the cycle anew. This creates a harmonic effect you feel as pulsed braking or shuddering. If fork flex reduced braking force there wouldn't be a problem, you'd simply squeeze the lever harder.

    I'm not 100% sold on the theory, but know of many who have solved or reduced shuddering by moving the fulcrum (cable hanger) down.

    I think the main cause of shuddering is more like a chalk on the blackboard effect, whereby the forward motion of the rim pushes the shoes forward twisting them to dig the heels in. This increases braking force until it slips back and repeats the cycle. This happens on all rim brakes, and causes the characteristic squeal, or shuddering. Greater braking pressure counteracts the twist by forcing the rims flat, so you only get the effect in mid-range braking. The cure has traditionally been to toe the shoes in so that the twisting actually helps align them, rather than digging the back in.

    I suspect that front cantis are very vulnerable to this because the forks aren't rigid enough to keep the bosses parallel under braking loads so the twisting begins to occur even without the forward motion of the rim. I've solved the problem using a combianation of a brake booster, and filing a bit of a ski tip into the heels of the shoes so there's no corner to dig in. Cleaning the rims also helps.

    All in all shuddering is a harmonic effect caused by a combination of issues. Often solving one is enough, other times you have to go after all of them. Whichever theory you subscribe to, address those issues first, and if that doesn't solve it, move on to the next.
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