Rear axle keeps bending.

Discussion in 'Mountain Bikes' started by RobbieIG, Oct 1, 2004.

  1. RobbieIG

    RobbieIG New Member

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    I have a 2000 Jamis Cross-Country. I've had it since late 2001, and it saw moderate and rare riding. This summer I started usuing it nearly daily as a commuter bike, and just recently I've actually been using it to mountain bike. However, in the past two weeks, it broke in someway every time I tried to use it. First, on the way to the trails, I was accerating from a traffic light, and I did this:

    http://home.comcast.net/~robbieig/crank/bent01.jpg
    http://home.comcast.net/~robbieig/crank/bent02.jpg
    http://home.comcast.net/~robbieig/crank/bent03.jpg

    Replaced, so I replaced it with a Shimano tripple crankset. The next time I was riding to the trails, the rear axle bent. I didn't realize what had happened...I just noticed that I couldn't get the wheel centered. Then, as I was going downhill after a big climb, the axel got so bent that the wheel rubbed on the left chainstay. Getting home was quite the chore.

    I replaced the axle and, in so doing, noticed some scarring on the axle cones, but my LBS didn't have any suitable replacements. So, I had to go with just the new axel. After about an hour of riding on the new axle, it bent again, going uphill, no jumps, not even really any rough terrain. But, once again, the back wheel was rubbing the chainstay. Luckily, it was mostly down hill, and I was closer to home this time. Upon removal, it was clear that the new axle, a supposedly stonger one, was bent.

    I don't know what I am doing wrong. I don't think it's me weight that is causing this, thought I am 310lbs the last time I checked. Afterall, if a 180lb man can take a jump on the same axel, I should be able to ride on the groung without bending one. And I have had no trouble at all on my fixed gear road bike.

    Anyone have any experience with this sort of thing? Should I spring for new bearings, a new wheel, new cassette? Switch to a solid axle and dump the quick release?

    Oh yeah, with the new crank set, I haven't been able to adjust the front deraileur to be able to shift to the shortest chainring. Is everything on this bike just crap?!

    Any help is appreciated.
     
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  2. dabac

    dabac Well-Known Member

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    For what's happening to your crank you need to consider strength as well as weight, but I've never seen a failure like that due to pedalling. If you hadn't said anything I'd assumed you'd hit the chainring on an obstacle to cause something like that.

    A solid axle would be stronger than a QR one but not by that much. IF your bike is a freewheel one you might consider switching to a freehub, which has wider spacing between the bearings that makes it stronger than a freewheel one.
    A fixed can be built with a shorter axle which can make it more durable.


    Your new crank probably haven't settled at quite the same position on the BB as the old one. You might come across BB/crank combos that aren't compatible, but probably yours can be fixed by adjusting the limiter screw on the FD and/or slackening the cable some.

    I just had a look at the Jamis website, and the current specs aren't that hot. It might just be that the bike simply can't take your riding. IMO frames and forks can take a lot of "average" use even from heavy riders, so one way forward could be to get yourself a rear wheel(and crank) built to DH specifications and take it from there.
     
  3. Juba

    Juba New Member

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    The stresses that are applied to a road bike are different then those placed on a mountain bike. Even tame off road trails will have some ruts, roots and rocks, which can cause jarring impacts.

    The bulk of mountain bikes and mountain bike components are designed for riders in the 160-180lbs weight range. Unfortunately, your body weight is stressing the components of your bike past what they were designed to handle, and they are breaking.

    As the previous poster mentioned, the solution is to upgrade any components you break with a stronger model. Freeride and downhill components are built to endure extreme stress, and would provide the longevity you are looking for. Specifically, the components that you might be looking at replacing are: rims, spokes, hubs (or just getting a new wheelset), handlebar, crankset, bottom bracket, fork, seat post and head set.

    One thing to consider is some companies make a line of bikes specific to larger riders. Kona for example has couple models, the Hoss and the Hoss Dee-Lux, which boast a larger, stronger frame and components that are chosen for their strength.

    Cheers,
    Juba
     
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