Bill Kapaun

Something you might want to check out is to see if the rim has been "wallowed out" from hitting a curb.
Take a caliper (a 12" adjustable wrench should work) and set it to the rim width.
Then, slide it all the way around the rim.
Wide spots can really throw you off if you aren't aware of them.

dabac

I've resuscitated several of bent rims and reinstated them for beater duty. My approach is to tape the spokes together at the cross, then remove the rim from the spokes completely. Hold against flat surface to determine where the bends are. If a sturdy work bench is available, I'll clamp the "flat" section of the rim to the table, with the bent overhanging the edge, then lean on it - heavily.
W/o sturdy bench I'll determine the high spots, then lay the rim on the floor with the high spots resting on a broom handle, hockey stick a pair of wooden blocks or whatever, then step on the rim. Sometimes I have to inch my feet towards the blocked up section to get a strong enough bend into the rim to straighten it out. Repeat until good enough or alotted time for the project runs out, relace rim into wheel, tension, true and ride.

This is at disassembly, something like 17 mm out.


This is after 1st round of bending, something like 11 mm remaining. Not good enough yet but a big improvement.


For some reason I didn't follow through on the photo shoot, I think I had to call it quits for that evening or something.
Anyhow, at the next session I got it down to abt 2 mm deflection, at which point it went back into the wheel.
So maybe I wouldn't/haven't taken it on a cost-to-coast tour, but it's so far it's doing fine.

I've never had much luck tackling serious bends with the rim still in the wheel, IME the opposite spokes won't allow for enough of a counter-bend to end up anywhere near to straight. I've had good results pushing out low spots with the rim still attached though.

Either way, it still a good hour's work or so. 20 minutes to secure the spokes and unscrew the nipples, 10 minutes of bending, and 30 minutes of reassembling the wheel. For me, that'd go a long way towards simply replacing the rim or building a new wheel from scratch.
If you have to pay someone for the time, this'll buy you a new budget wheel from the LBS.

cny-bikeman

You don't seem to understand that if the spokes have no tension at all that there is no way for them to hold the rim in a consistent position - it can shift randomly. The suggestion to hold a flat rim against it would tell you definitively or sighting across as FB suggests might help.

Now that being said, if it is really true (and we don't know yet for sure) that the rim has two large areas that are bent, 180 degrees (opposite) from each other the prospects of getting the rim back in shape are not great. One has to be very careful not to bend the rim too much when working on each one to not introduce another bend, and the fact that they are large and gradual will make that task difficult.

You should not need a link to videos - just Google straighten bent bicycle wheel, study several video and text explanations of the entire process and then pick one or a combo that feels right to you. If you think it's straight but find wide variations in spoke tension among the spokes on one side you still wil not have a very strong or stable wheel. It may be better than before, may not.

The moral of the story is to either not lend out your bike or have friends responsible enough to compensate you when they damage your possessions.

dsaul

As several others have mentioned, you really need to use a straight rim next to the bent one to see the bends if you don't want to disassemble the wheel. However, if you had a straight rim you should just use that instead of the bent one. To easily disassemble the wheel, use a bit of masking tape on each spoke crossing before removing the nipples. This will keep the spokes in the proper place and save you from having to learn how to re-lace the wheel after you straighten the rim. It will also make it easy to lace the new rim on after you discover that the old one is beyond repair. Seriously, a new rim is not that expensive and it will save you a lot of trouble.

FMB42

I agree.

The time spent attempting to true a damaged rim by hammer and/or blunt force will almost always exceed the cost of a new rim. The fact is that you might not ever be able to fully trust the so-called "fixed" rim again. This is not to mention the possibility that you'll end up stretching certain spokes beyond use (if you haven't done so already). There is a point where being cheap just doesn't pay off in the end....

The bottom line here is that your friend, at the very least, owes you a new rim.

If your friend isn't willing to pay the price for the damage he/she has done then I'd get both a new rim and a new friend.

ultraman6970

You need 3 pieces of wood and a hammer to fix that rim wheel.

wphamilton

Couldn't you cut a rim-sized hole (minus a couple inches) in a large sheet of stiff cardboard or corrugated plastic and lay that against the rim to find the bent spots?

Burton

Building a wheel up with a new rim is about a 45 minute job. I'm guessing a lot more than that has been spent fooling around so far. The best advice I've seen so far is to strip the rim - maybe cause thats what I do myself.

In any case - an independent rim can be checked against any relatively flat surface - including a wall, and straightened a lot easier too. Not that its 'easy' to straighten a rim - it'll take more force than you think. Perspnally I wouldn't consider using a hammer for anything except impact damage on a steel rim. On an aluminum rim you risk deforming the width and compounding the problem.

Marking off the out of round areas, supporting the low spots with multiple 2x4's, carefully balancing your weight on the opposite high spots (yeah - stand on it) and bounce a little. Do it gradually and don't expect instant results. Rims are surprisingly tough. With a little work you can bring most rims back to 99% both horizontally and vertically.

A new rim is usually a more cost effective solution unless its an expensive rim, but you've already said that's not an option.

cny-bikeman

It's the rider not the bike, it's the mechanic not the tools.

ksisler

[partial QUOTE=TwoFourOne;15270377]Alex ID19 rims, 32-spokes (F & R), Formula quick-release hubs;
Long story short, my friend crashed my bike and untrued my rear wheel. I fixed it up as much as I could and let it be. It kept getting more and more out of true over time, and I realized that the rim is probably bent. The spoke tensions became very unequal and it got to the point where some driveside spokes were REALLY tight and some NDS spokes were REALLY loose, but the rim was still pulled towards the NDS. Also, (obviously), the overall spoke tensions became very unequal.

After reading for a while, I figured I'd completely de-tension the wheel to 1) see if the rim is bent, and 2) re-tension the spokes correctly (or, at least more correct than they were before). So, I un-tensioned every spoke. I loosened them all the same amount, so the thread on the spoke is JUST covered up by the nipple (as recommended by Sheldon Brown). Now, how do I determine if the rim is actually bent? I'm not sure. [/QUOTE]

OP; As others have pointed out; unless you take the rim off the wheel you are basically hosed. Most consider that the correct way to tell if a rim is bent is to put a new straight one overtop of it and look for gaps... As one way to avoid the hosing; Walk around with "detensioned wheel" and look for a big trash can or a barrel that is the right size to set the wheel on. Of course a truing stand might be a good thing to have access to for this purpose...just say'in

OP: Back to your Q on how to fix; If the crash was bad enough to wank up the wheel, then the rim is clearly bent. It comes down to the value of your time verses the cost of a new rim.
-- When considering the cost of your time, be sure to add more hours for the first pass at frutzing around with it, plus add time for the next 4 or 5 times you have to miss a ride because you have the wheel back under repair yet again to get it good enough to almost be right. Add a bit more for retruing on the side of the road at mid-ride when you start to hear the rim slapping on your brake pad (or your chainstay).
-- Another benefit of replacing your rim is the opportunity to closely examine all the spokes and nipples. I have found a goodly number of bend wheels also showing partially stripped nipples and spoke threads leading to a long session on the truing stand with a wheel that just won't come back to true and won't tension up correctly. An hour wasted on the stand pretty much pays for a new rim.

Not wanting to seem to be picking on you, but hope this helps.

/K

FBinNY 

If the OP is still sweating hot to tell if a wheel is flat while it's laced loosely here's a quick and easy way using stuff he has at home.

You'll need a flat table bigger than the wheel. It doesn't have to be precisely flat, any dining table will be fine, though a folding card table probably wouldn't be. Then you'll need four objects of identical height. Drinking glasses would be OK, but if you don't have a matched set, 4 cans of soup would be perfect and probably match closer than you tell with the naked eye.

Now arrange 3 cans on the table to support the rim at 3 roughly equidistant points. The 4th can is your gauge, and you can move it around under the rim. If the rim is flat, it'll be the same height over the table all the way around, and the gauge can will be a kiss fit below. OTOH a warped rim will rise and fall so the warps will be easy to find with the gauge.

Al1943

Before spending a lot of time trying to straighten the rim, check very closely for small cracks near the spoke holes and for any signs that the spoke nipples are trying to pull through the rim. Cracks are fatal to a rim.

davidad

Tie the pair of spokes together where they cross and dissamble the wheel. Now you can figure out exactly where the rim is out and start to bend it back. I would put the high spots between two blocks of wood and stand on it until it bends back. You need to do a little at a time to keep from going the other way. Good luck with it.

TwoFourOne

I appreciate the discussion going on here. Thanks for everyone's replies.

I'll disassemble the wheel (using tape to keep groups of spokes together, to make it easier to reassemble), and then go from there. I'll update everyone when I get to that point.

For the record, I'd much rather problem solve and do labor on my own bike for 5 hours than pay for a new rim. I enjoy the challenge And I also have two bikes, so no ride time is lost.

TwoFourOne

Alright, I unlaced the rim. I now have the hubs+spokes (and the nipples), and a completely bare rim. I laid it on the flattest surface I could readily find, and tried to make notice of the bends.

In this picture, the red spots are coming toward you a lot, and the pink spots are coming toward you a little bit. I'm not sure how high the bend is (didn't have a ruler on me), but I'd guess it's about ~10mm.



Thanks for this! But can I ask if this will still work in my case? Cny-bikeman gives off the impression that it's hard to fix. Wouldn't I just put the rim on wooden blocks, so that the high spots (red in my picture) are on the blocks, and then put a lot of pressure on the unbent (white in my picture) parts of my rim? Both sides at once (ie, standing on both unbent sides)?

pierce

or block the straight parts then push down on the high spots. your call.

that rim sounds pretty wasted to me.

dabac

There's a reasonably good chance, but no promises.
Sometimes the bends are just too local, too sharp to come out well.
If the rim is just pinned at the seam, it may come apart as you try to straighten it.
Now, the seam coming apart isn't critical as such (it'll pull together once you start tensioning the spokes again), but it may prevent you from getting enough leverage to straighten the bend.

Difficult is a null word in these circumstances. Making it better - easy. Making it serviceable - readily manageable. Getting it really, really good - tedious and difficult. And its hugely dependent on the characteristics of the rim, the nature of the bend, and your sense of judgement/skill.

That's how I'd do it, but there are undobtedly variations on the theme that'll do just as well. Keep a few different blocks, or paperback books or basically anything sturdy with a non-marring surface available and start low, something like the 2" range. Safer to work up to avoid overshooting.

That'll ultimately be decided between the characteristics of the rim and the nature of the bend.
I start like that, but I often end up having to move my feet closer to the bend to get the desired result.
Like this:
-let's say you have high spots at the 6 and 12 o'clock positions, and those are resting(hump side down) on blocks
-first step on to the rim at the 3 and 9 o'clock position, bounce a little.
-inspect
-put rim back, step on to the 10 and 2 o'clock position, bounce a little.
-step onto the 4 and 8 o'clock position, bounce a little
-inspect
-If required repeat the above with higher blocks, or feet closer to the high spots.

TwoFourOne

Thank you so much for that post, dabac! That's exactly the kind of explanation I needed My wheel is all fixed now, your advice worked perfectly.

I used some school textbooks to put the wheel on, and then I stood on it. I was too light to make any big changes so I had to get my friend who's about 20 lbs heavier than me to help me out. He stood on it and pressed down pretty hard, and the wheel gave and bent back. It was almost perfect after that - not *completely* perfect, but good enough (and infinitely better than how it was before).

Then I laced the wheel back up, and worked on truing it. I followed Sheldon's guide (and a few others), and in an hour or two I think I did a pretty good job at putting the wheel back together. I trued it laterally, then I dished it, trued it laterally some more, worked on equal spoke tensions, stress relieved, lateral truing, etc, etc. I made sure to do a really thorough job on stress relieving the spokes. When I took it for the first ride, there was no pinging or anything at all, so I think I did a good job on that.

Overall, the wheel is as equal in spoke tension as I can get it without a tension meter, and it is pretty true laterally and radially (I had to sacrifice some true-ness for equal spoke tension). The rim is almost as good as it was brand new. Perhaps even better because I took care in building it back up really strongly.

Thanks everyone for your help! If the rim explodes or whatever, I'll be sure to update this thread. But for now, it seems to have worked perfectly

bobotech

See, much easier to straighten the rim after you disassembled it! Good job! I wish you had taken some pictures of the rim before and after working the bend out, would have been interesting to see.

TwoFourOne

Yeah, it was. I did have pictures of the rim before, but I deleted them already. Didn't take any of the rim after. I should have.