Re: "Catastrophic" failure of mountain bike fork lowers (Manitou Skareb Comp)

Discussion in 'Cycling Equipment' started by Marvin, Feb 11, 2005.

  1. Marvin

    Marvin Guest

    Phil, Squid-in-Training wrote:
    > The magnesium lowers of my 2003 Manitou Skareb Comp had begun to

    crack last
    > year, about 6 months before I stopped riding it. I've kept it

    stashed away
    > for a while until today, when I was cleaning my room and found the

    lowers.

    If you manage to lose an entire set of fork lowers in your room you're
    very nearly as messy as I am :)

    > My experience:
    > From the first day I bought the bike, the front wheel had always

    rubbed the
    > v-brake pads when turning. I thought this was just because it was a

    light
    > bike (23lb Giant XTC2). But as I continued to ride, my expectations

    turned
    > to frustration, as the larger tire that I had put on was actually

    beginning
    > to rub the arch when braking hard. This wasn't really a problem

    until I
    > began riding more aggressively. It was at that point that noticed

    that the
    > wheel was beginning to get cocked to the side with the mere

    application of
    > weight. I knew this was out of the norm and searched for the

    problem, which
    > I found in the form of a crack in the fork leg that contained the

    coil
    > spring. New updated lowers with a beefed-up arch/leg join were sent,

    and I
    > installed them without a hitch. After another 2 months of use, I

    broke the
    > damping assembly inside the fork. Rather than fix it or pay to have

    it
    > fixed (I wasn't working at an LBS at the time) I left it as it was,
    > spring-only. After another 3 months, I acquired my current bike

    (Giant
    > STP2) and a Fox Vanilla. The Skareb with the updated, uncracked,

    flexy
    > lowers was put aside.


    Just to add my voice, I've had one of these reverse-bridge forks fail
    on a customer's bike. It doesn't seem to be safety-critical since he
    only noticed it when the clunking noise and fork flex really got on his
    nerves and he inspected it a bit more closely. Since the legs can't
    fall off and the skewer is still tight, there's no short-term potential
    for a catastrophic failure. More mileage would probably twist and snap
    the QR skewer, at which point you really would be in trouble, but my
    customer got round the rest of a fairly tough off-road ride with no
    worse problems than his fork legs walking around and crapping up his
    steering (disc brake still worked fine). As soon as we removed the
    wheel the lower legs twisted around quite independently and freely, but
    the axle and skewer seemed to hold them enough for him to get home.

    It definitely looks like a design problem, right on that sharp corner
    where cornering stresses and the asymmetry between spring and damper
    cartridges combine. The fact that it also seems to be quite a flexy
    design in a material that doesn't like being flexed suggests that
    Manitou really weren't thinking all that carefully during the design
    phase.

    Bottom line: yes they're a bit of a suspect design, no failure wouldn't
    necessarily have resulted in a faceplant.
     
    Tags:


  2. Werehatrack

    Werehatrack Guest

    On 11 Feb 2005 02:07:18 -0800, "Marvin" <[email protected]> may
    have said:

    >Bottom line: yes they're a bit of a suspect design, no failure wouldn't
    >necessarily have resulted in a faceplant.


    The tips of the tubes, where the QR clamps, are also mag alloy. I
    suspect that they'd break off before the skewer would fail...but it
    would take a while. The greater danger would be if the arch failed
    during a bumpy downhill run; the asymmetric flex could put the wheel
    into one tube enough to give just the added amount of unwanted braking
    to produce an endo.

    --
    My email address is antispammed; pull WEEDS if replying via e-mail.
    Typoes are not a bug, they're a feature.
    Words processed in a facility that contains nuts.
     
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