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Old 12-06-11, 04:45 PM   #1
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Bump Bump Bump One Very Loose Spoke on Rear Wheel

I could feel a subtle but periodic thump coming from my rear wheel, transmitted up my seat stays to my saddle. I sensed this around the time I installed new tires. Thinking it was related to the tires, I switched back to my old ones. The thump was still there.

I observed the wheel while riding and noticed one spoke on the left side that bowed outward more the the rest. Sure enough, it was incredibly loose; however, the wheel ran true. I have not yet adjusted spoke tension and re-trued the wheel, but...

Would having a wheel that basically runs true but has one spoke (effectively) missing produce the phenomenon that I am experiencing? [This may be a good question for Jobst Brandt!] Has anyone experienced something similar? Thanks!
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Old 12-06-11, 06:06 PM   #2
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having one spoke loose or missing can cause this, especially with low spoke count wheels. just replace, true and it should be fine.
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Old 12-06-11, 07:44 PM   #3
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I would guess a bent rim (flat spot) causing the loose spoke and the bump.
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Old 12-06-11, 07:55 PM   #4
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32 spoke Dura Ace Hub with Mavic Open Pro wheel, double butted spoke.
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Old 12-06-11, 08:04 PM   #5
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runs true laterally but not radially? gradual or sharp bend?
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Old 12-06-11, 08:42 PM   #6
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This wheel was not properly equilibrated so that all spokes on a given side share the load equally, so absent any kind of spoke retention compound on the spoke or in the nipple, the unloaded spoke unscrewed itself.

The fix is simple: assuming the rim is not bent, using some form of tension measurement, balance the tensions, then using very small turns, bring the wheel back true and round.
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Old 12-07-11, 02:06 AM   #7
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If it runs true, but creates a bump, and it isn't the tire, then it pretty much has to be a flat spot. Bringing the spoke back to tension will in all likelihood promote the overall life of the wheel, but will not get rid of the flat spot. Some have reported being able to bend back flat spots, but I've never had any luck with that.

In theory, it could be a high spot as well. But you won't get a high spot from only one spoke dropping out. Maybe it's been there all the time and you've just recently picked up on it. Basically not associated with the loose spoke.
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Old 12-07-11, 10:23 AM   #8
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If it runs true, but creates a bump, and it isn't the tire, then it pretty much has to be a flat spot. Bringing the spoke back to tension will in all likelihood promote the overall life of the wheel, but will not get rid of the flat spot. Some have reported being able to bend back flat spots, but I've never had any luck with that.
I ht a pothole once that dented my rim (Open Pro- Ultegra). It was a little worse than the OP's and caused 3 loose spokes. I made a jig and bent the rim back round. This worked pretty well and made a nice laterally and radially true wheel.

But, after about 500 miles, the rim started to fail at the former flat spot and I replaced it.

With the OP's rim with less of a flat spot, he might get away with straightening the rim, but I would just replace it.
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Old 12-07-11, 10:31 AM   #9
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Correct me if I'm wrong but I think the thump the OP is describing isn't the rim but rather the spoke flopping around every revolution. I had a 36x3 wheel that did this, but that was before I knew anything about mechanics so it was never fixed. Wheel was straight and true at the time.

OP: just get the wheel re-tensioned and trued, should be a simple repair.
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Old 12-07-11, 11:01 AM   #10
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Funny... I have had wheels with multiple broken or missing spokes and felt nothing, but a slightly out-of-true, or slightly improperly seated tire can almost always be felt through the saddle.
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Old 12-07-11, 02:07 PM   #11
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Correct me if I'm wrong but I think the thump the OP is describing isn't the rim but rather the spoke flopping around every revolution.
Now that's the kind of stuff I was looking for! The subtle thump that I was experiencing MAY have actually been from the spoke buckling with each revolution due to inadequate tension. It was only really perceptible on really smooth pavement. That particular spoke happened to be adjacent to section of the rim where it is joined and I was concerned that it might have something to do with the joint failing.
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Old 12-07-11, 02:30 PM   #12
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Wheel maintenance was skipped for too long. that includes tensioning and truing.

If the rim has a seam rather than welded, there is a set of pins across that gap
and the aluminum extrusions are rolled in compression, they don't 'come apart'

Further, the spokes pull together increasing the compression across the seam.

Last edited by fietsbob; 12-07-11 at 02:35 PM.
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Old 12-08-11, 06:56 AM   #13
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.. The subtle thump that I was experiencing MAY have actually been from the spoke buckling with each revolution due to inadequate tension.
Unlikely. With double-walled rims (which yours are), the spoke would be free to move quite a bit down/out before encountering any resistance. Perhaps if the nipple has seized to the rim, which in itself also is unlikely.
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Old 12-08-11, 07:19 AM   #14
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True.
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Old 12-11-11, 07:01 AM   #15
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My bad — On close inspection (in the truing stand) I have found a very localized "flat" spot on the rim, right at the point where it was joined. Also, there is some evidence of damage (perhaps from a pothole) as there is a slight notch in one side of the rim in this location.
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