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Total Wheel Breakdown

Old 07-06-06, 08:08 AM
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thomson
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Total Wheel Breakdown

My son was riding an MTB last night with a Mavic X517 rear rim. All of a sudden the bike feels quite wobbly. Every spoke was loose, real loose. There were no broken spokes and the rim was straight. I trued it up and there were no issues there (so far anyway).

My questions, what causes this? Is it likely to happen again?

Thanks in advance
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Old 07-06-06, 09:57 AM
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Boy I would check the hub flange and make sure it is not bending or separating from the hub.

The only other reason would be a failure of the outer wall of the rim (the wall that is adjacent to the inner tube, not the wall that you see the spokes coming out of). It may be that the spoke nipples rest on this wall and pulled through if the rim is a hollow box construction.

I would remove the tire and inner tube to examine to make sure a catastrophic failure is not in the making.
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Old 07-06-06, 10:20 AM
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Originally Posted by antiquebiker
Boy I would check the hub flange and make sure it is not bending or separating from the hub.

The only other reason would be a failure of the outer wall of the rim (the wall that is adjacent to the inner tube, not the wall that you see the spokes coming out of). It may be that the spoke nipples rest on this wall and pulled through if the rim is a hollow box construction.

I would remove the tire and inner tube to examine to make sure a catastrophic failure is not in the making.

Thanks for the tips.

I checked the hub (XT btw) and it looks intact. I removed the tire/tube and there are no signs of cracks inside of out.

Still stumped....
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Old 07-06-06, 11:40 AM
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Originally Posted by thomson
Thanks for the tips.

I checked the hub (XT btw) and it looks intact. I removed the tire/tube and there are no signs of cracks inside of out.

Still stumped....
Maybe the rim was undertensioned from initial buildup, and recent humidity/weather conditions lowered the nipple thread friction. Then, under the stress of going over a bunch of bumps, nipples started vibrating off when they were at the bottom of the wheel (where the bump and rider weight further lower spoke tension).

This happened to the first MTB wheel I ever built. I got it built up, and the first ride was Porcupine Rim in Moab. Loosened the spokes right up. That's what I get for diving into a wheelbuild without reading ANY literature on the art beforehand. I did retension it, and that wheel lasted me about 3 years of very hard MTBing. It finally got a couple flat spots from my lack of finesse on the descents. That was 15 years ago...
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Old 07-06-06, 11:49 AM
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Originally Posted by waterrockets
Maybe the rim was undertensioned from initial buildup, and recent humidity/weather conditions lowered the nipple thread friction. Then, under the stress of going over a bunch of bumps, nipples started vibrating off when they were at the bottom of the wheel (where the bump and rider weight further lower spoke tension).

This happened to the first MTB wheel I ever built. I got it built up, and the first ride was Porcupine Rim in Moab. Loosened the spokes right up. That's what I get for diving into a wheelbuild without reading ANY literature on the art beforehand. I did retension it, and that wheel lasted me about 3 years of very hard MTBing. It finally got a couple flat spots from my lack of finesse on the descents. That was 15 years ago...
This seems likely given the circumstances (I have no information on the origin of the wheel, but it has been performing OK). But is it possible to go from somewhat loose to all of them very loose all of a sudden?
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Old 07-07-06, 11:13 AM
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I have had that happen too.

I think that it was alot less sudden than you think that it was. Much like feeling a ridge on a surface, your finger can tell you if it is smooth or there is a ridge, but there is only a few hundred thousanths of an inch as far as you are concerned between a smooth and ridged surface. If you would have put the wheel to some sort of measurement last week you probably could have easily have seen the wheel was sloppy, but with no measuring device, it had to be great enough to feel the one pound difference between tight and loose.

Grab a handful of spokes once in a while and squeeze, even the untrained hand can tell the difference between tight and loose spokes long before you will sense the gentle fishtail through standing up on the petals.
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Old 07-07-06, 03:57 PM
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Originally Posted by Section 8
I have had that happen too.

I think that it was alot less sudden than you think that it was. Much like feeling a ridge on a surface, your finger can tell you if it is smooth or there is a ridge, but there is only a few hundred thousanths of an inch as far as you are concerned between a smooth and ridged surface. If you would have put the wheel to some sort of measurement last week you probably could have easily have seen the wheel was sloppy, but with no measuring device, it had to be great enough to feel the one pound difference between tight and loose.

Grab a handful of spokes once in a while and squeeze, even the untrained hand can tell the difference between tight and loose spokes long before you will sense the gentle fishtail through standing up on the petals.
You might be right. The person riding it is new to cycling and may not have recognized things were squirelly underneath him. In any case, I trued it up to proper tensioin, dished it, and there is no hop. He is on his first ride with it since (offroad to the beach) I told him to grab a hunk of spokes before he leaves so he knows what it should feel like and to grab a hunk when he is at the beach.

I am hoping that the spokes were somewhat undertensioned and loosening slowly until it reached some critical point and then they all collapsed. It is altogether possible that he rode it with quite a bit of wobble before he thought there was a problem. In any case, he knows what to watch now.

Thanks for all your suggestions, comments, etc
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