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  1. #1
    mtbr member
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    Mar 2010
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    379

    203 mm front brake rotor and a qr fork

    I've seen this being a not advisable set up in a couple of threads. Is it true that 203 mm front rotors and a qr 9 mm axle are not a good mix? Or is that just under certain circumstances? I have a Marz AM fork, and have had 203 mm rotor on the front (along with Avid BB7 brakes) for a couple of years. I've even DH'd with it without any trouble. Mind you, I haven't done any huge jumps, or double black runs.

    What's the word? Should I downsize to 185 up front?

  2. #2
    mtbr member
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    Jul 2003
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    6,674

    If the fork in question...

    was originally rated for a 203mm or larger rotor then it should be fine. The problem initially croped up with older design forks that had completely vertical drop outs. The front disc brake when applied vectors the force of decleration in a downward and back direction. Under the right circumstances this could force the qr out of the drop out. There were also instances of cracked dropouts on lighter duty forks. However in recent years most fork manufacturers have gone to an angled dropout that is canted forward and gives support to the axle that counters the downward pull when the brake is applied. Some, like Fox have gone with the angled drop outs on all their QR forks. Others like Rock Shox have only gone to the angled drop out on forks that are intended to use the larger rotors. Of course this isn't an issue with thru axel forks.

    I would check with Marzocchi and see what your current fork is rated for. And reduce the rotor size if necessary. With all that said, there is no clear set in stone pattern that indicated any specific fork manufacturer or model was more prone to this happening. So there were or are obviously variables involved. I think riding style had the biggest influence on the problem. So I would find the max recommended rotor size for your fork and go with that. Oh and at the time the problem first surfaced it wan't happening to just new forks, used forks were involved as well. So just because you've been running 203s for a couple of years doesn't mean it couldn't happen.

    Just check it out and be safe.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

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