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  1. #1
    poser/hipster/whatever xthugmurderx's Avatar
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    Fork shudder. Why?

    Any ideas as to why a fork shudders? what part of the fork is to blame? The legs? Are some too thin? Which forks shudder?

    Easton EC90X. Shudder. Big time.
    Alan Cross Fork. Carbon legs/steerer. Alloy crown. No shudder. Why? Is it due to the extra 100g? If so, it's totally worth it.

    I just want to avoid it. Trying to see what I can do.

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    there are many reasons why a fork shudders..the fork, the brakes, the brake pads, the cable...take your pick. someone said that when they switched to v brakes, the shudder was gone. the amount of grab of the pads and the power of the brakes.
    fogriderlooking for sun

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    Don't smoke, Mike. shapelike's Avatar
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    Quote Originally Posted by xthugmurderx View Post
    Any ideas as to why a fork shudders? what part of the fork is to blame? The legs? Are some too thin? Which forks shudder?

    Easton EC90X. Shudder. Big time.
    Alan Cross Fork. Carbon legs/steerer. Alloy crown. No shudder. Why? Is it due to the extra 100g? If so, it's totally worth it.

    I just want to avoid it. Trying to see what I can do.
    Well what's different?

    Same brakes on both bikes? Same brake pads? Same style of housing stop on the steerer tube? Are both the bikes in the same condition (is one on filthy, gummed up wheels/pads while the other has been gone over with emory paper and methyl hydrate on the rims and pads)?

  4. #4
    big ring MIN's Avatar
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    When switched to different rotors on my disc brake equipped bike, shuddering went away. Sometimes the micro-vibrations caused by braking can sync with the natural resonant frequency of the wheel or fork and cause shuddering.

    Solution: toe your brakes more or try different pads.

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    Quote Originally Posted by xthugmurderx View Post
    Any ideas as to why a fork shudders? what part of the fork is to blame? The legs? Are some too thin? Which forks shudder?

    Easton EC90X. Shudder. Big time.
    Alan Cross Fork. Carbon legs/steerer. Alloy crown. No shudder. Why? Is it due to the extra 100g? If so, it's totally worth it.

    I just want to avoid it. Trying to see what I can do.
    There was a really good explanation posited on this a few months back, but I haven't been able to find it for you. I'll try and restate it here, but I could be off a little. To a certain degree, all fork blades flex back and forth when going over uneven terrain - be it road bikes or cross bikes. The theory (that I'm buying into until I hear a better one) on shutter is that on cyclocross forks with cantilever brakes, the flexing back of the fork blades actually increases the distance between the front brake housing stop and the brake cable fixing bolt on the brake, causing the brake to tighten down harder as the fork flexes back. As the brake tightens, the fork returns forward quickly. This is repeated during hard braking and you have your shutter.

    Shutter seems to be more prevalent in the lighterweight cross forks paired with strong cantilever brakes. The stronger the braking force and the less stiff the fork, the greater the shutter. Toeing in your canti pads effectually weakens the initial stopping force of your brakes, and can reduce the shutter. You still will get it when you squeeze down hard on the brakes though. In my experience, brake shutter isn't that big a deal in cross races, but if you use your cross bike for road training, it can be downright scary on fast and twisty road descents.

    So back to the source, this theory has pinpointed the relationship between the upper cable stop and the brake fixing bolt as the problem. If this theory were to hold true, then brakes that have the housing run straight into the brake arm, such as linear pull and disc brakes, would not be subject to the same type of shutter. I haven't personally witnessed any major shutter with these other two brakes, but if other folks have, then it might be back to the drawing board with shutter theory.

  6. #6
    shoot up or shut up. isotopesope's Avatar
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    a fork mounted cable hanger could fix the theory dragonmg explained... if your fork is drilled for one that is. v brakes can still shudder as well, if not set up properly. especially those dumb shimano parallel push ones, using cartridge pads.

    it's probably your brake setup though. it seems a light weight fork just exacerbates any brake setup issues. on my old cross frame with a kinesis aluminum fork, i had shuddering really bad until i got my dumb old avid 6's set just right... i had to toe them in rather extremely... like 3 mm. i then installed a wcs fork, which shuddered like crazy too. non cartridge black koolstops sort of helped, but no matter what setup black magic i used, my brakes either shuddered hard initially, or somewhat during hard braking, or had no power, or squealed. sanding the pads and rims helped as well. i had to pick two problems ultimately. i settled on slight shuddering under hard braking and low overall power. i could not completely get rid it of with that fork... until i switched to xt canti's, which magically removed all shuddering and increased overall brake performance significantly.

    now that the xt's are on my crosswind with a zornyc fork, they still work great. that fork is beefcake! i've known a few people to get their avid's to work fine. i had my wife's old soma braking fine with avid 4's... but i also know folks that got rid of all of their brake issues when they got rid of their avid's.

  7. #7
    poser/hipster/whatever xthugmurderx's Avatar
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    interesting. the only difference was the fork. same brakes, and same pads. actually, both forks also had the cane creek brakes on them, which didn't shudder so bad, but the didn't stop. kool stop pads and some red extreme condition pads (forget brand. not koolstop). Using the shimano R550's currently.

    I dunno. It isn't an issue in racing, but on the road. i commute on my cross bike, and intersections aren't much fun. Not a HUGE deal, but i just thought I'd see if anyone knew anything.

    the question was more in regards to a project i'm working on. I'm importing my own frames and forks, and when it came time to make up a cross fork, I just wanted to make it as shudder free as possible. It seems to me that a grabby brake/pad combined with a lightweight fork blade would make shudder happen. just the act of the brake grabbing the rim, and the fork blades flexing with the force. That was my theory. Dunno if it's legit.

  8. #8
    Just ride it. MrPolak's Avatar
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    I thought shudder applied only to Cantis since the brakes' effective force is dependent on the tension of a very long cable. The tension of this cable is temporarily lessened when the fork flexes which allows the fork to snap back, which increases the tension and so on. An oscillation sets in and if the frequency of this oscillation is low enough it will be perceived as shudder. This can be exacerbated as the pads move over an uneven or dirty braking surface.

    Mine shuddered until I cleaned the pads and wheels - I have a carbon fork with Shimano Canti brakes.

    It seems that if excessive fork flexing is the culprit then one of these should fix it:


    Last edited by MrPolak; 02-26-08 at 11:15 AM.

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    Quote Originally Posted by isotopesope View Post
    my dumb old avid 6's set just right...
    Apologies for going OT, but does anybody else think it's about time Avid went and revamped the Shorty brakes already after like eight years using the same dumb design? I mean they function okay and all, but is there a worse straddle cable quick release in the entire bike industry?

  10. #10
    crosser
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    mini-v brakes do never shutter

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    Just ride it. MrPolak's Avatar
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    Quote Originally Posted by Elmar Schrauth View Post
    mini-v brakes do never shutter
    And I'm planning to upgrade to mini-v brakes! Actually I'd like to go with disc brakes bu there's a small issue of finding 700c disc wheel that are Campagnolo-compatible.

  12. #12
    Don't smoke, Mike. shapelike's Avatar
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    Quote Originally Posted by MrPolak View Post
    And I'm planning to upgrade to mini-v brakes! Actually I'd like to go with disc brakes bu there's a small issue of finding 700c disc wheel that are Campagnolo-compatible.
    Jtek shiftmate, American Classic cassette are two options that come to mind as a possible solution.

    How's the braking power with mini-v brakes though?

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    I tried a mini V on my Surly forked Gunnar, and they stopped OK without shudder (unlike my Avid Shorties). However, I was using normal Shimano brake levers, and I had to set the mini Vs approximately a nanometer from the rim in order to get reasonable lever travel. That close, they wouldn't open enough to remove my 28mm tire. I'm going to try something else, either a new cantilever or a fork mounted cable stop.

    Eric

  14. #14
    shoot up or shut up. isotopesope's Avatar
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    Quote Originally Posted by seat_boy View Post
    I tried a mini V on my Surly forked Gunnar, and they stopped OK without shudder (unlike my Avid Shorties). However, I was using normal Shimano brake levers, and I had to set the mini Vs approximately a nanometer from the rim in order to get reasonable lever travel. That close, they wouldn't open enough to remove my 28mm tire. I'm going to try something else, either a new cantilever or a fork mounted cable stop.

    Eric
    what length arms were your mini v's? 80 or 85 mm?

  15. #15
    Soma Lover
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    Quote Originally Posted by xthugmurderx View Post
    the question was more in regards to a project i'm working on. I'm importing my own frames and forks, and when it came time to make up a cross fork, I just wanted to make it as shudder free as possible. It seems to me that a grabby brake/pad combined with a lightweight fork blade would make shudder happen. just the act of the brake grabbing the rim, and the fork blades flexing with the force. That was my theory. Dunno if it's legit.
    I actually had to go to a grabbier brake pad to get my Soma Double Cross to behave itself. The brakes woke the dead with their squealing and as I went to softer and softer pads (now using Aztecs) the squeal moderated itself into a slight shudder at a lower resonant frequency. Lengthening the straddle cable about 6-8mm lessened the shudder to a point which is admittedly less than perfect but less than obnoxious as well. With a short, almost straight across straddle cable the magnification of the braking force by the fork flex is magnified greatly.

    I've also had a terrible time with the headset (a cheapie Aheadset the LBS just happened to have in stock) coming loose. When it's a bit loose, the fork flexes a bit more and the shudder gets noticeably worse. The last time I tightened it was the last time I'm going to tighten it. I'm planning on replacing the headset and Soma fork with a Chris King and straight blade IRD. We'll see how it goes. I'd prefer to go back to a slightly harder compound as this also serves as a 2000+ mile/year commuter and resetting the toe-in every month is a PITA.

    BTW, I didn't do it to fix brake squeal but when I went to Thinline Pads to fit beefier tires on my Jamis Aurora it also got rid of the relatively mild brake squeal it had. I guess a millimeter less arm trying to "twist" the brake was enough.

  16. #16
    crosser
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    best length is 85 mm

  17. #17
    Al noisebeam's Avatar
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    Quote Originally Posted by dragonmg View Post
    TIn my experience, brake shutter isn't that big a deal in cross races, but if you use your cross bike for road training, it can be downright scary on fast and twisty road descents.
    Yep. I don't race CX, but do ride on trails with it and there I don't even notice the shudder.

    On the road however it feels unsafe to the point that I am uncomfortable on such roads you describe.

    The bike I have problem with is a Lemond Poprad w/canti brakes. I started with the aluminum fork and went thru many fine tunings with LBS, all the tricks of pad angle adjustment, pad material, etc. tried, but with no good results. Lemond, in response to my complaint that the shudder was a safety issue, sent me a new carbon fork. That helped a bit, but the shudder is still there and still too dangerous for fast decents. It is quite easy to get the front wheel to start skipping on pavement on decents due to shudder. That is quite disconcerting.

    It is unfortunate. I love this bike and while I can still use it on trails, no longer use it on the road. My other bike is a fixed gear and I ride it 99% of the time now - I want to use the Lemond for routes that are not good for the fixed (i.e. hilly routes with steep descents) but that is unsafe on the Poprad.

    So I either need to convert to a road fork and different brakes or buy a road bike.

    Al

  18. #18
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    noisebeam--try subbing in the tektro cr720 as a front brake.

    I had some nasty squeal and shudder with my Avid Shorty 4s and koolstop pads. No longer, and I'm running the stock tektro pads as well.

    they are fairly cheap as an experiment to do.

  19. #19
    Al noisebeam's Avatar
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    Quote Originally Posted by comradehoser View Post
    noisebeam--try subbing in the tektro cr720 as a front brake.

    I had some nasty squeal and shudder with my Avid Shorty 4s and koolstop pads. No longer, and I'm running the stock tektro pads as well.

    they are fairly cheap as an experiment to do.
    Thanks. Yeah, I still have the Avid Short 4s with salmon koolstop pads.

    Al

  20. #20
    Senior Member sfcrossrider's Avatar
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    Fork shutter can lead to fork breaking. Be careful.

  21. #21
    crosser
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    Quote Originally Posted by sfcrossrider View Post
    Fork shutter can lead to fork breaking. Be careful.
    yes ,thats my opinion ,too.

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    I ride a Ridley Super Cross with the 4ZA Python fork, one of the lightest forks, and 4ZA Canit brakes, and I have no issues with shuddering. The LBS owner filed the bosses so the brakes fit perfectly, and told me that would prevent any shuddering. Does the brake fit to the fork make the difference? It would explain why the same brake on a different fork might not cause shuddering.

  23. #23
    Get the stick. darkmother's Avatar
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    I had the the same problem with my CX bike a couple years ago. Try a fork mounted cable stop for canti brakes. It's cheap, and it works. Mini V's, or full sized V brakes with a travel agent also work. Sometimes oldschool MTB cantilevers with the big fat "brake pad on a stick" design also help (as opposed to the newer ball and socket thin V-brake style pads.

    Good luck,
    Jeremy

  24. #24
    M_S
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    I've gotten the shorty 4s on my cross bike to stop shuddering almost entirely by toeingthe brake pads. When they wear out (they're close) I'll get some Kool Stops and hopefuly that'll do away with shuder completely.

    Yeah, shudder is worse on the road, but honestly I'm used to it. Maybe it's that it's been a couple years since owning a bike with calipers? Cantis require a somewhat different technique, but I do lots of long mountain descents without issue.

    For what it's worth my cross bike has the stock K2 carbon fork which seems pretty beefy but it hardly the most overbuilt thing out there either.

    I also have to strongly second the comment about headset loosness. I flipped my stem once and didn't tighten things down enough. The first time I braked after going out it felt like the fork was going to shake right off the bike. I don't mean to suggest that all the people having shudder isues don't know how to tighten a headset (most of you have probably been working on bikes longer than I've been alive) but I do wonder if it might be exacerbating the problem for lots of folks.

  25. #25
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    Switch from mini V's to Cantis = SHUDDER!

    To validate DrangonMG, (who explains the length of cable from the housing to the brake itself on canit's causes forks to shudder)... it's must be true! I had NO shudder whatsoever on a Specialized Tricross w/full carbon fork and stock Tektro mini V's, when I decided to install new cantis because the mini V's had such minimal clearance to the rim, I couldn't remove the wheels w/o deflating tires, or loosening cable anchor bolts. Any minor WoW in the rim resulted in brake scrub when pedaling hard, so I decided to switch 'em out this year. The moment I installed Cane Creek SX5 Canti's., VIOLENT brake shudder erupted! WTF, I asked myself?! I got brand new brakes w/Koolstop pads (grey), toed in excessively , clean and true rims. I was perplexed, as I thought it was my STIFF looking fork legs that defeated fork shudder so commonly found on cyclocross bikes. NOT SO! DragonMG's explanation makes sense. The excess of cable between the housing and the brake itself is the issue.

    I resisted trying Travel Agent's as one cable fraying and breaking is too much for me (besides the look goofy and seem like they'd add friction). I will try the fork mounted cable housing stop if I can get away with it (2cm minimum req between straddle cable and cable stops), or cave and go back to the mini-V's with an adapter like the Travel Agent.

    My advice as a mechanic, salesperson and racer to any of you experiencing fork shudder: DON'T PUT UP WITH IT. It is NOT SAFE and NOT ACCEPTABLE no matter what some of these fools think. Sooner or later, you'll eat SH$T because your stupid set-up failed you, causing you to loose traction. Manufacturers MUST here from riders that the designs are NOT WORKING to evoke change.

    (and no rim-to-brake clearance OR cable adjustment barrels, unfortunately)

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