Rigid fork stutter- Mtbr.com
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  1. #1
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    Rigid fork stutter

    Hi,

    I went for a ride today and just discovered that my rigid fork stutters when applying the front brakes. I checked the qr, the rotor and caliper bolts, none were loose.

    The set-up is a steel frame with an on-one 29er steel rigid fork. I have been using this bike for close to a year now but recently changed to a hope x2 tech brakes from avid bb7. The bb7s worked fine however they were not as powerful as the x2s. The x2s took a while to break in and when it did, it had lotsa power and i'm guessing it make my fork stutter.

    The stutter is only noticeable going downhill on paved roads while applying the front brakes only. On the trails else is ok.

    I'm guessing that it could be the longish steel fork i'm using, plus its a 9mm qr. Not too sure if a thru-axle rigid fork, or a carbon fork, would reduce the possibility of such stutters thou.

    Hoping to see if anyone also encountered the same problems could provide some solutions... TQ!

  2. #2
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    Sounds like the fork flexing fore/aft as the brake is applied. I had the same on two separate set ups: Pace carbon MTB forks and Hope M4/185 and on my 29er with steel lugged forks and Avid SD7/Paul Lever.

    Neither failed or affected the ride at all.

    SSP
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    Otis Guy talking about klunkers c1976

  3. #3
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    Did you ch-ch-ch-check the headset to see if it's worn?

  4. #4
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    I agree with SeaBass_. The headset is just a wee bit loose. It probably could use a repacking, but a slight tightening of the top cap bolt (after first loosening the stem binder bolt/s, of course) should do the trick.

  5. #5
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    Oh, and King headsets make it worse...not having (up till now) the conical collar the O-ring could squish and make it judder.

    Cane Creek or WTB for me now

    SSP
    "Put any one on one of these singlespeed bikes and they could not help but have fun"
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    Otis Guy talking about klunkers c1976

  6. #6
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    It's the Hope's.

    Last month I switched out my Hayes for Hope and the stutter shows itself in exactly the same situations as you described. Rotor is the free-floating ragged looking ones, fork is a Salsa cro-mo.

  7. #7
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    If all fails, take a look at the rotor is it mounted the right way (gyro fwd), and is the wheel laced accordingly (spokes on the rotor side girando fwd).

  8. #8
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    Are your front rotors warped?

  9. #9
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    I had that years ago with a very expensive bontrager composite fork and it drove me nuts.I actually wrote to Keith Bontrager and he recommended toeing my brake pads a bit more than usual.I think in the end i got pissed off with it and sold the fork.If you have a powerfull disc brake on a steel fork that probably is thin walled with a average weight wheeland tyre on it then i am not really suprised.Size of the rotor and the power of the brake is the number one culprit.The bb7 didnt do it (!)says it all.

  10. #10
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    How heavy are you, most likely the stutter is in the fork legs. Very light steel forks or even worse Ti legs have been known to stutter. I used to ride IRD Expedition forks and the Ti had a terrible stutter unless the brakes were severly toed in. The Aluminum was better but not by much. I also had an old Litespeed Ti fork that wasn't much better. You may be better off trying a different fork.

  11. #11
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    I have an On One carbon fork. I use BB7 brakes with Alligator Windcutter rotors. I also have brake stutter. But just like you said, its only on the road going down a steep hill when I am trying to go slow. I don't notice it anywhere else I ride. So I don't think affects anything, and I just keep riding.

  12. #12
    Retro Grouch
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    Quote Originally Posted by cactus
    Hi,

    I went for a ride today and just discovered that my rigid fork stutters when applying the front brakes. I checked the qr, the rotor and caliper bolts, none were loose.

    The set-up is a steel frame with an on-one 29er steel rigid fork. I have been using this bike for close to a year now but recently changed to a hope x2 tech brakes from avid bb7. The bb7s worked fine however they were not as powerful as the x2s. The x2s took a while to break in and when it did, it had lotsa power and i'm guessing it make my fork stutter.

    The stutter is only noticeable going downhill on paved roads while applying the front brakes only. On the trails else is ok.

    I'm guessing that it could be the longish steel fork i'm using, plus its a 9mm qr. Not too sure if a thru-axle rigid fork, or a carbon fork, would reduce the possibility of such stutters thou.

    Hoping to see if anyone also encountered the same problems could provide some solutions... TQ!
    Just brain storming. #1 make sure you are using an internal QR such as a Shimano and that the lever side is opposite the disc (the nut side of a Shimano QR has steel teeth that grip better); I have had a disc brake pull a QR half way out of a front dropout with a weak external cam QR. Also, since the shutter only shows up on paved roads it could very well be your tires. I have 4 mountain bikes with rigid forks and I noticed a distinct shutter with some tires.
    Just one more rep and I get the toaster!

  13. #13
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    Maybe the disc pads are a tad bit high hitting the rotor?

    Haven't had any stuttering issues going with BB7s on Redline, Surly or KHS rigid forks.

  14. #14
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    WD-40 the pads.

  15. #15
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    I have the same problem with my 29er Monkey and BB7's. Set your front inboard (static) pad as close to the disc as possible so your rotor has less deflection when the front brake is applied. This helped to lessen the fork stutter but did not eliminate it. I run Avid SD7 levers, and I set the front for Max. modulation and just go easy on the front brake on steep
    paved descents. It's like adjusting your brake balance.

  16. #16
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    thanks for all the help and suggestions guys...

    just to add, my headset is not loose and i'm using a2z teppan yaki sp4 180 rotors mounted correctly on a proper 180 adapter and they are not warped. tires are 2.1 smallblock8s and the bike is a 69er set up and i'm 176lbs but i don't think those matters much.

    the problem didn't exist before and i have changed nothing except the brakes from a bb7 to hope x2s.

    i'm really thinking its the brakes being too powerful for the set up. long steel fork legs plus QRs probably make them parts rather springy.

    i'm gonna change to a full 26er set up with on-one carbon fork and maybe add bolt-on skewers, maybe that may help. wouldn't mind a thru-axle carbon rigid fork either but i know not of any.

    else i think i might have to live with it and use my rear brakes more... it only happens on paved roads anyway and it's not noticeable in the trails. don't really feel like going back to bb7s just because of this...

  17. #17
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    Quote Originally Posted by cactus
    it only happens on paved roads anyway and it's not noticeable in the trails. don't really feel like going back to bb7s just because of this...
    Rubber gets more traction on the pavement. Use a little more rear brake on the tarmac and you'll be good
    Happiness depends more on the inward disposition of mind than on outward circumstances. Benjamin Franklin

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