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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 10-04-05, 06:07 AM   #1
Jay H
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How to fix a flat spot on a rim?

Have a rear tire (MTB 26" Bontrager Maverick) on my commuter MTB that appears to have a flat spot. I've tried to true it but I can feel on the rim that the end of it bows out a bit. Of course, the rear brakes catch on it at low speeds. I know it's going to be dangerous come this winter when I'm commuting and my rear tire decides to lock up in the middle of a turn, so I want to fix it.

Any suggestions on how? I'm thinking of removing the tire/tube and using some pliers to try to carefully straighten out the rim, or perhaps using wood and a clamp and then the pliers to try to distribute the force. Anybody have any pointers on fixing this myself? It's not too drastic but it's enough to be annoying and possibly dangerous in icy conditions.

jay
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Old 10-04-05, 06:24 AM   #2
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it would be like trying to fix a giroscope that is out of true and bent, a flat spot can not be fixed and you are correct in it being dangerous.

you will need a new rim for sure
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Old 10-04-05, 08:19 AM   #3
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First loosen the spoke in the area of the bulge. Then use visegrips with care to squeeze the in the bulge in the rim. If one side is still bulgeing use a flat piece of metal under the visegrip jaw to spread the load on the flat side. Retension the spokes and check for radial trueness. See also Sheldon Brown

http://www.sheldonbrown.com/tooltips/truing.html
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Old 10-04-05, 09:47 PM   #4
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If you actually flattened the rim - a small flat section on the round rim should be visable from both sides, NOT just side to side play.
A flat spot on the rim feels like your hitting a bump every time the spot rotates to the ground. - you need a new rim!
If if only hits the brakes each revolution - it can be "trued" by turning the spoke nipples. If the wheels only need truing - http://www.parktool.com/repair/readhowto.asp?id=81
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Old 10-04-05, 09:56 PM   #5
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With a new rim.
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Old 10-04-05, 10:44 PM   #6
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When i took my old wheel into an LBS with a flat spot, they told me it was useless to try to fix it. The guy said that some ghetto shops would try to fix it with a hammer and a couple blocks of wood, but that the rim would be ruined that way anyway..
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Old 10-05-05, 02:49 AM   #7
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There is actually a device that will pull flat spots out of rims if they're not terribly bent. The fact that such a tool exists is sort of a moot point because first you hve to find a shop that has one and talk to a person that knows what it is from all the other relics collecting dust on the wall from before the days of strong alloy rims and cheap pre-built wheels. Then you'll probably wind up paying about the same to fix your old rim as you will to just buy a new one. But the tool DOES exist.
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Old 10-05-05, 06:20 AM   #8
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Thanks guys, if the rim is indeed toast, there is no harm if I carefully try the block of metal and some pliers. I think the spokes are true as I do have a cheapo Minerva truing stand and looked at it there. Just that the rim is slightly bent outwards (one or both sides) that I can try to carefully bend back in.

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Old 10-05-05, 07:55 AM   #9
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I had the problem with a Mavic Ksyrium Elite that had been crashed. I figured I couldn't harm anything by experimenting. Tried all sorts of things; hammered it, stomped on it, hung it from a tree limb... Never did get it in perfect shape, but had a fun time playing around with it and honing my wheel truing skills! Ended up getting a generic 20 hole rim off eBay and rebuilt the wheel.
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Old 10-05-05, 10:17 AM   #10
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As you squeeze the sides of the rim in, that part of the rim will be forced out radially, so finish the job by putting the wheel back in your trueing stand.
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