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  1. #1
    Join Date
    Sep 2006
    Location
    Oslo, Norway
    Posts
    3,934

    thumping rim brakes... haaalp

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    Ok so my commuter bike is an mtb with rim brakes. The rear brakes are crappy (don't spring back properly and need replacing), but the front brake isn't a joy to use either. Loud thumping and shaking ensues.

    So I assume there's a wobble in the wheel that I can true out. But I have the wheel out now in the stand, and it is pretty true. There's one spot that I think is causing the thumping, not a big wobble, but an abrupt one. The adjustable measuring thingys on the wheel stand "catch" very clearly on this point. But it's not a skew to one side, the rim flares out to both sides! So how do I fix that? There's no way of tightening spokes to make the whole rim narrower at one point, is there?

    I'm thinking of just grabbing the entire rim with a large pair of pliers and squeezing it together, but there seems to be a pretty big chance of just creating worse bumps. Gentle hammering?
    Winter riding is much less about badassery and much more about bundle-uppery. - malkin

    1995 Kona Cinder Cone commuterFrankenbike/SI SLR Lady Gel Flow
    2008 white Nakamura Summit Custom mtb/Falcon X
    2000 Schwinn Fastback Comp road bike/Jett

  2. #2
    Join Date
    Jul 2010
    Location
    Austria
    Posts
    374
    Maybe sanding paper would work? Maybe you could attach it somehow to the brakes or the measuring thingy and just turn the wheel until the bump is at least less noticeable?

  3. #3
    Join Date
    Apr 2006
    Location
    Maine
    Posts
    950
    Unfortunately that is what is known as a "flatspot'. If you're careful, you could take pliers or something to try and pull it back, but also remember that there's a potential to have the entire rim move slightly. And, you're likely to have a concave spot where you just moved the rim.

    At any rate, good luck with your project!

    http://chasecyclery.blogspot.com

  4. #4
    Join Date
    Sep 2006
    Location
    Oslo, Norway
    Posts
    3,934
    Thanks The wheel is otherwise good, so I want to keep it. I took a humongous pair of pliers and squeezed the rim together as hard as I dared along the inch or two that was flared. It seemed to be a little less abrupt afterwards. A gradual flare doesn't seem to be a problem for braking, just this sudden bump. Sanded it a little afterwards to remove the burrs from the pliers, and adjusted the brake pads to catch a little lower down on the rim, since I assume the flat spot (nice term!) is most noticeable near the edge, and least pronounced towards the centre of the wheel.

    I won't get to test it until I brake hard at speed, but I think I've done what I could

    And I'm going to the lbs to pick up some new brakes for the rear tomorrow. I've put it off for ages, but they're not getting any better and are not reparable.
    Winter riding is much less about badassery and much more about bundle-uppery. - malkin

    1995 Kona Cinder Cone commuterFrankenbike/SI SLR Lady Gel Flow
    2008 white Nakamura Summit Custom mtb/Falcon X
    2000 Schwinn Fastback Comp road bike/Jett

  5. #5
    Join Date
    Sep 2006
    Location
    Oslo, Norway
    Posts
    3,934
    Darn. It didn't work. The thumping is maybe a little bit less pronounced, but very much still there. Next step I think is a vice, maybe after some careful heating.

    Good point is - these rims seem to be a lot more solid than I thought!
    Winter riding is much less about badassery and much more about bundle-uppery. - malkin

    1995 Kona Cinder Cone commuterFrankenbike/SI SLR Lady Gel Flow
    2008 white Nakamura Summit Custom mtb/Falcon X
    2000 Schwinn Fastback Comp road bike/Jett

  6. #6
    Join Date
    Apr 2006
    Location
    Maine
    Posts
    950
    I love your adventuresome spirit LPH

    FYI: a flat spot is generally created when we hit some sort of pothole, crack, etc...

    Hope the wheel doesn't give you any more trouble

    http://chasecyclery.blogspot.com

  7. #7
    Join Date
    Sep 2006
    Location
    Oslo, Norway
    Posts
    3,934
    Thanks

    I'm suprised that this wheel has this spot (out!, out, damned spot!), because it's on a bike that I very rarely flat with. I'm usually riding pretty fat mtb tires, and at worst hopping up and down curbs.
    Winter riding is much less about badassery and much more about bundle-uppery. - malkin

    1995 Kona Cinder Cone commuterFrankenbike/SI SLR Lady Gel Flow
    2008 white Nakamura Summit Custom mtb/Falcon X
    2000 Schwinn Fastback Comp road bike/Jett

 

 

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