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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 06-05-07, 08:58 PM   #1
Kommisar89
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Fixing a flat spot on a rim

I'm a mechanical neophyte with bicycles so pardon if this is an obvious question but is it possible to fix a flat spot on a rim. I've had wheels that were slightly out of round because some spokes were too tight and I could fix that by retensioning but I have two wheels right now that seem to have a very slight flat spots, just enough to be noticeable and annoying while riding. It's hard to notice with the naked eye but on a truing stand you can see that there is a flat spot that is a few millimeters low. The problem is that the spokes in that area are as loose as I can reasonably make them. It would seem that the rim itself is slightly bent. Is there a way to repair that short of replacing the rim? I took it to one LBS but they had no solutions. Thanks for your suggestions.

-Derrick
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Old 06-05-07, 10:34 PM   #2
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need to find an lbs who has a tool for removing the flat spot. The only shop In Denver that I know has the tool is Cycle Analyst.
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Old 06-05-07, 11:35 PM   #3
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You could buy the tool yourself, but even their tool tip says the only real fix is replacement. A replacement rim is probably cheaper than the tool...though you'd have to swap it out yourself or pay labor.
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Old 06-06-07, 08:42 AM   #4
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You could buy the tool yourself, but even their tool tip says the only real fix is replacement. A replacement rim is probably cheaper than the tool...though you'd have to swap it out yourself or pay labor.
That's interesting - I actually envisioned something like that like a couple blocks of wood and a hydralic jack (hey I've watched a few episodes of the Red Green show ). They don't seem to have much confidence in their tool though. Might be worth a shot bringing to a shop that has one. My wheel isn't tacoed, it's only 3-4mm out of round.
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Old 07-21-07, 06:06 AM   #5
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I have an old repair book which shows a similar method - you loosen/detach the spokes in the affected area, place that area at "6:00" on the ground, run a wooden board across the top of the 6:00 rim surface, stand on either side of the wood board, grab the top of the wheel (at 12:00) and pull up hard (use your knees, not your back!).

That jack tool is pretty nifty, tho.

I am having a similar vertical dip issue, but am leaning towards replacing the rim....
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Old 07-21-07, 06:21 AM   #6
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I've read of using a large wood dowel or hammer handle to literally beat the dent out of the rim. You loosen the spokes, hit the low spot with the handle or dowel until it is out to the right contour and retension the spokes. Does it work? Dunno but it sounds interesting if crude.
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Old 07-21-07, 08:46 AM   #7
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The book mentions that one too (This is Bicycling's book from the late 80s). They say both techniques are crude but worth a shot, especially with an expensive rim. After all, if it doesn't work, you'd be no worse off than just buying a new rim in the first place........
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Old 07-21-07, 09:11 AM   #8
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As stated before, any repair to a flat spot is crude, but my favorite has always been to use a dead-blow hammer. They're available at most hardware stores, have a plastic covering and lead shot inside the head. It's also a great universal tool, but use with care, as it can move things very easily. I would think it would take forever to move the rim with a hammer handle or dowel, unless you're talking about hitting them in turn with a hammer. the dead blow is a much better choce. I like the 20-24 oz size best.
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Old 07-21-07, 09:12 AM   #9
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They say both techniques are crude but worth a shot, especially with an expensive rim. After all, if it doesn't work, you'd be no worse off than just buying a new rim in the first place........
So how good of a wheel are you looking for? When do you stop on the rebending process?

If your standard for roundness is 1mm or 2mm, that's a pretty hard target to hit using such crude methods. When you finish messing with the rim there's still the even spoke tension issue to consider.

Bite the bullet. Replace the rim. Fix your bike right so that you can ride free from worries.

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Old 07-21-07, 11:41 AM   #10
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Is it hazardous to ride on a rim with a slight flat spot? My rear wheel(an Ambrosio 19 Elite, 27") has one. LBS mechanic said I could lose my rear tire! I don't plan on riding on it, just curious.
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Old 07-21-07, 01:28 PM   #11
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Is it hazardous to ride on a rim with a slight flat spot? My rear wheel(an Ambrosio 19 Elite, 27") has one. LBS mechanic said I could lose my rear tire! I don't plan on riding on it, just curious.
The mechanic is going on the theory that the tire won't seat in that area. I've worked on a lot of tires with flat spots and have not seen blowouts to be a common issue at all. The main risk is that the wheel is generally much weaker.
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Old 07-21-07, 02:31 PM   #12
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Yeah, I just had the rim replaced. I'm a cheap SOB but sometimes you just gotta do it. I doubt safety was ever an issue. You could barely see it with the naked eye so it wasn't much of a dent but it was definately something you could feel while riding. Very annoying. Guess I just need to learn how to build wheels so I can do it myself next time.
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Old 07-23-07, 09:04 AM   #13
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Bite the bullet. Replace the rim. Fix your bike right so that you can ride free from worries.

Yeah, I am definitely doing so, I just wanted to mention those methods seen in the book. And again, no harm in trying (assuming you don't strain your back when pulling up on the wheel!)


Just for the record, I am having trouble reusing the (new) folding tire that was on the flattened rim....maybe the rim deformed the tire bead?
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Old 07-23-07, 09:06 AM   #14
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Yeah, I just had the rim replaced. I'm a cheap SOB but sometimes you just gotta do it. I doubt safety was ever an issue. You could barely see it with the naked eye so it wasn't much of a dent but it was definately something you could feel while riding. Very annoying. Guess I just need to learn how to build wheels so I can do it myself next time.
we are cut from the same cloth, friend.

I really want to learn to build me own wheels. I sold my truing jig a few years back (twas an old crude one anyway, I do just as well for lateral truing tweaks on the bike, using the brake shoes) but wanna get the new Park shop-quality stuff......
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