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Fork judder

thecremeeggthecremeegg Posts: 284
edited July 2010 in MTB workshop & tech
Since I put a 203mm rotor on my Rebas, when I brake the fork flexes noticeably. Is this normal? As far as I know the fork is rated up to 210mm of disk

Posts

  • Chunkers1980Chunkers1980 Posts: 8,035
    How do you mean flexing - in what ways?

    That's a big rotor - generally the bigger things are the more they flex...

    Take it you have a QR version?

    The 20mm Reba has noticably less flex than a QR one all things remaining constant.
  • thecremeeggthecremeegg Posts: 284
    Yea its a QR one. The fork seems to flex from the stantions, I didnt notice it before but now it is quite noticeable
  • Chunkers1980Chunkers1980 Posts: 8,035
    How much flex is there if when not on the bike you hold the bars and just the front brake and rock it forwards and back? Do they flex then?

    Is your headset tensioned correctly?
  • Chunkers1980Chunkers1980 Posts: 8,035
    Also are they post mount or IS brackets- might not matter but with a rotor that size you'll have to have a lot of hardware.
  • thecremeeggthecremeegg Posts: 284
    How much flex is there if when not on the bike you hold the bars and just the front brake and rock it forwards and back? Do they flex then?

    Is your headset tensioned correctly?

    They dont flex much when I do that, and the flex doesnt seem to be coming through the bars, its literally the lower stantions that move.

    And the brackets are post mount
  • rubins4rubins4 Posts: 563
    I got a 203 front disc with a set of toras, and they flex. I think there is just too much stopping power for the rigidity of the fork to deal with. Just come back from cornwall where there are some serious hills which can really test the power of the brakes, especially on roads where there is plenty of grip for the brake to work against.

    As it goes, I'm actually down sizing to a 160 disc, but the flex isnt the reason why, think you just need to be more progressive with the lever maybe? It never worried me too much, but I know it was certainly there
    http://www.bikeradar.com/forums/viewtop ... t=12613038
    Anyway, fk dis, I iz off 4 a ride innit. l8rz peepz
  • supersonicsupersonic Posts: 82,708 Lives Here
    Most fore aft flex comes form the stanchions, crown and steerer, a bolt thru will not cure this.

    Theoretically the flex will be the same with a smaller rotor as the maximum braking is governed by tyre grip, not the rotor. So if you can lock up with both, then I think it should be the same. Though you will notice more for less lever pull of course.
  • joshtpjoshtp Posts: 3,966
    dont worry about it, most forks judder and twang a little under heavy braking, and a bigger disk will make the stoping force greater, and the twang more noticable.... even my ultra stiff AM140 magura thor's, well renound for being very stiff judder a little.

    its notmal.[/img]
    I like bikes and stuff
  • thecremeeggthecremeegg Posts: 284
    Cheers guys, I'll leave them be and if they break and I die then I'll come haunt you all ;)
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