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  1. #1
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    Insane vibration ONLY when locking rear wheel.

    Hey! i'm not one for asking for help but this has got me stumped and I'd appreciate and help or advice on a nagging vibration/ juddering coming from the rear wheel when I lock it up.

    The bike is a 2013 Rose Granite chief 6.
    Rear wheel- DT Swiss Tricon M1700
    Brake- Formula T1 180mm rotor
    Tyre- Hans Dampf Trail star
    The suspension on the rear is of the Horst Link variety(4 bar linkage)

    The bike runs sweet but everytime I skid the rear wheel the rear end vibrates like a jack hammer!!

    I don't believe it's a brake issue as they perform perfectly until I lock the disc completely and then the wheel appears to judder back and forth in the direction of wheel travel.

    These tricon wheels have fewer spokes than a normal wheel and i'm starting to think it has something to do with this although I would imagine there's thousands of these wheels running disc brakes without issues!

    I've purchased a splined spoke tool and tried tightening each spoke a half turn- No joy and then a further half turn- still no joy but this felt too tight anyway so I backed them off to the original tension.

    I've sent Rose an e-mail but thought I'd try and get some feed back on here too while I'm on.

    Many thanks G.

  2. #2
    El CicloPath!!!!!!!
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    Is your quick release tight enough? Are you a heavy rider? Are there any loose pivots? Are the caliper centered over the disc? Is there any play in the bearing of your hub?

  3. #3
    El CicloPath!!!!!!!
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    And btw, if you are riding public trails,myou probably want to avoid skidding anyways. It contributes to ruining the trails.

  4. #4
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    Ok .........now that you got told to stop skidding, my guestion is rear suspension. maybe the trouble is there. Maybe try messing around with dampening or the psi . Is the shock worn out ?

  5. #5
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    Quote Originally Posted by Fachiro1 View Post
    Is your quick release tight enough? Are you a heavy rider? Are there any loose pivots? Are the caliper centered over the disc? Is there any play in the bearing of your hub?

    Yes all the above are fine. I'm 14 stone which I'm fairly confident isn't excessively heavy for the bike. The bike's only a month old and it's done this from new, which is a shame as it's a fantastic bike!

  6. #6
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    Quote Originally Posted by Vader1 View Post
    Ok .........now that you got told to stop skidding, my guestion is rear suspension. maybe the trouble is there. Maybe try messing around with dampening or the psi . Is the shock worn out ?
    Ordinarily I would think the same but the bike is brand new and I've tried grabbing the rear triangle when it vibrating and it makes no difference.

  7. #7
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    I'll take a shot at this. If you lock the back wheel on a hard tail, it tends to bounce around quite a lot. I'd imagine that you're experiencing something to do with resonance. Try changing the PSI in the tire a little one way or the other, because I suspect it's nothing to do with the brakes, and everything to do with some magical alignment of the tire resonating, the wheel resonating, and the suspension/bike resonating. Changing one thing in the setup may completely eliminate or greatly reduce your problem, and tire pressure is an easy thing to start with.

  8. #8
    Rub it............
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    Your getting rear wheel bounce. Once the rear wheel starts bouncing, it transmits it directly into the suspension, causing an endless up/down motion in the rear suspension until you release the brake.

    It's resonance. Try modulating the rear brake better to avoid rear wheel lockup.

  9. #9
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    Skidding hmm.. I really can't recall the last time I fully locked a rear wheel riding XC-DH, especially @ speed. As suggested try modulating your brakes. Locking brakes only increases your stopping distance. Either your brakes have a massive amount of "grab" or your hand does.

  10. #10
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    Quote Originally Posted by xcr2000gt View Post
    Ordinarily I would think the same but the bike is brand new and I've tried grabbing the rear triangle when it vibrating and it makes no difference.
    how are you able to grab the rear triangle when youre locking up the brakes while riding?
    Put a mountain biker in a room with 2 bowling balls and we'll break one and lose the other - GelatiCruiser

  11. #11
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    Quote Originally Posted by keen View Post
    Skidding hmm.. I really can't recall the last time I fully locked a rear wheel riding XC-DH, especially @ speed. As suggested try modulating your brakes. Locking brakes only increases your stopping distance. Either your brakes have a massive amount of "grab" or your hand does.
    Regardless of braking efficiency, there are occasions when sliding the rear end is desirable and/or happens unintentionally and having the rear wheel shake itself to death is not an ideal outcome.

  12. #12
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    Quote Originally Posted by SandSpur View Post
    how are you able to grab the rear triangle when youre locking up the brakes while riding?
    With great skill and dexterity

  13. #13
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    Almost never desireable to skid for real riding (maybe in a panic to make a hairpin turn instead of going off a ledge). Unintentional, yeah, it happens.
    Looking at the website for your model, it looks like the shock has a lockout (or at least position selector, I didn't read for details). Try a different lockout setting. Also try shifting your weight back in conditions where this is likely to happen to load the rear wheel and suspension better.
    As mentioned, the wheel is trying to pull "backwards" compared to the bike motion, and since it's attached, it can't, and kicks UP instead. On your bike's design, that "upwards" wheel motion translates almost directly straight into the line of the shock. If the shock is locked out (or overpressure for the rider weight), it has minimal allowed forward motion. This causes it to jackhammer right back into the seatstay bars, back at the wheel, slamming it back down (a Specialized FSR has an "s" curve axle path where it actually travels back a little, then up and slightly forward, then back again near the end, this virtually kills any "judder" caused by bracking (and brake-jack). Without technical diagrams it's hard to tell, but just eye-balling your model, it appears it's a more linear "wheel straight up, seatstay straight forward" path. Probably slightly more plush than the Specialized path over knobby terrain, but the tradeoff is brake jack, which you are seeing. Not much you can do, but if the shock isn't normally ridden wide open, try it open and see what happens, that should allow the suspension to kick forward (and stay somewhat compressed while braking) without the violent rebound effect, at least reducing the brake jack. Shifting weight back will assist in that.
    If you shift weight forward when hard braking, AND have a locked out shock, your bike is going to do that, nothing else you can really do about it.

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