PimpMan

I have single wall rim that is bent inward about 3mm on the areas marked with red, is there way to fix it? How i go about it?

P.S. Its cheap bike i don't want to invest more money into new rim, need to be able to tighten spokes.

andrewclaus

This article has some ideas.

Iride01 

If the rim is still useable and spokes and other parts aren't needed, then it might only cost a little bit to have a shop true it up for you. If this is a front wheel, I'd want to know that it is all in good order. I've seen the results of a front wheel bending like a taco shell. You don't want that to happen to you.

FBinNY 

To start, I'm assuming you're speaking of a wheel, with a rim.....

This a classic wheel alignment. Probably not "alignment 101" but certainly part of a more advanced level.

in a nutshell, fixing it involves relaxing the spokes near the low zones, and tightening in the high zones to pull them in and bulge the low spots out. The amount of skill involved depends on the severity of the problem, but if you have decent hand skills, you can probably do OK after reading a few tutorials.

As noted above, eyeball the rim for any cracks or intense local flaws before wasting time on what is likely scrap metal.

PimpMan

Ahhh easier to buy a new rim than take out spokes and do all that after i just changed all spokes int hat rim.

PimpMan

Tried that and it sort of worked however rim is not really an oval so it was not easy to fix. Then it was a rear rim so i had to tune one side 120kgf and other 70kgf and there problem oval reappear again.
Also i was not able to dish rim without having few spokes tension set to 160kgf i guess its bent too much and best to scrap it.

FBinNY 

Please note that rims are usually pretty round when you buy them. If you laced this wheel then odds are that YOU introduced the error when you tensioned the spokes. Keep in mind that the spokes shape the rim, not the other way around.

I say this, because you seem to be headed in a direction where you'll spend more money only to end up with the same or a similar result.

If, as I inferred, you built this wheel, you now have to finish the job by allignining it.

PimpMan

I was fixing someone's bicycle that was in pretty bad shape, i should have checked rim before changing spokes on it.

Iride01 

Not only checked on the rim, but read a book or some articles about building wheels for bicycles and truing them.

Spokes aren't just a remove and replace operation if you want it done correctly.

FBinNY 

What I said still holds true. Unless you're dealing with an extremely rigid rim with a relatively deep profile, or one with a pronounced flattened zone, odds are that it's not the rim, it's you.

Most radial hop is introduced early on by tightening spokes unevenly, and is VERY difficult to resolve once the spokes have significant tension. The key to dealing with hop is not to introduce it in the first place.

Before spending dough try this the following (worst case, you'll waste some time, but learn something in the process.

1- loosen this wheel to fully slacked spokes.
2- decide on a gauge for in initial spoke turns. You can use a screwdriver with a pin that pushes it out at a certain spoke depth, or simply put a thumb nail on the last thread, and bring all the nipples to that.
3- add 2 full turns to all right side spokes, if that doesn't cause meaningful tension (otherwise tighten right, loosen left to establish the 2 turn differential. That's will establish approximate dish early on.
4- working by degrees turning all nipples the same amount. ie. half turns all the way around, and repeating, until the wheel is at roughly 1/2 the desired final tension.
5- do a first rough alignment (don't obsess because it'll change, but get the wobble within reason, say 5mm TIR. (total wobble)
6- using only right spokes align focusing 90% on hop, and get overall roundness to within 1-2mm TIR. This is critical because it's easy to final true for wobble, but not for hop
7- check dish, and dial that in. I usually work either all right or all left based on the tension so far.
8- you should have a reasonably true wheel at mid-high tension. Align it as you would, again close, but not obsessive.
9- add tension, keeping in mind that the left spokes exert more sideways pull than the right, so it's like 1/2 turn on all right spokes, then 1/4 turn on all left. Recheck alignment and dish
10- as you get close (say 80-90% tension goal) tighten tighten ONLY right spokes, so that you end up with a slightly over dished wheel, and true close to final specs (<1mm hop, <2mm wobble)
11- add final tension with left spokes, while bring dish back home. This is a bit of a touch thing. I generally can hit my target tension during this step, and barely have to touch the tighter right spokes again.
12- final true for wobble and hop, keeping in mind that right spokes have greater effect on hop, and left on wobble.

Whether or not this will work with this rim is unknown, but the practice, and understanding how the process works will serve you well on all future builds.

PimpMan

I know its the rim because even with all spokes loose as possible i turn it in the frame and it shows severe radial bending.

Thanks for the guide i try it when i build other rims.

Way i tighten the spokes is usually like this.
1. i build the wheels
2. turn all spokes so only little bit of thread is visible at the hub side of the spoke nipple
3. turn all spokes 3 full turns
4. turn all spokes 1 full-turn or half-turn at a time before i feel tension by hand.
remove spoke tension
5. check pressures with spoke gauge and adjust to remove any lateral bending
remove spoke tension
6. deal with radial bend if any, usually there is none.

FBinNY 

It's your dime, and your choice ---- But

I'd be remiss if I didn't make a last effort to convince you that rims like this have near zero rigidity compared to the loads imparted by the spokes. Your sketch indicates a rim that any halfway decent mechanic could bring into true, probably to within 1mm radial TIR. (discounting the weld or joint)

79pmooney

This sounds like a bent rim. If so, no amount of truing will make it a good wheel. It needs to be bent back to close to true, the trued as usual to the best that can be achieved.

Bike shops used to have 'dent pullers" (that also wore several other names) designed to pull out inward bends. They looked a little like a dishing tool only narrower and far stronger with a solid hook that laid flat against the inside of the rim. You loosen the spokes over the indent, place the tool against the outside of the tire (left inflated on the rim to protect it), tighten the screw to bring the hook against the rim then tighten further to pull the rim out to just past the surrounding area. Tool off, spokes tightened and if done right, rim is quite ride-able. (The metal will work harden and not "unbend" perfectly so the end result will not be perfect or beautiful.)

This fell out of favor with the new, much stronger aluminums that are nowhere near as malleable as those of the '70s. And with today's lawsuit crazy environment, those tools are now a big liability to shops. I think they are now all stored in a facility resembling Fort Knox. I want one. I'm now building wheels to ride using old tubular rims but things have happened to them both on-bike and accidents in storage, etc. So if any of you reading this has one that should be sent to that fort, you can send it to me and trust that the only rims it ever touches will be mine.

And funny story - re: wheels with side-to-side bends. Here, that tool is no help. But like the inward dents, only bending back to straight will make good good repair. At the shop I worked in, those wheels went to our master mechanic. He'd tell the customer it would take hours and to come back later. Customer out the door, he'd loosen the appropriate spokes, grab the wheel (again, tire on and inflated) and slam the sidewall on a concrete step. Tighten nipples and be done. 10 minutes. (Customer sent away simply so he never saw that!)

Until modern aluminum, these were standard practices.

FBinNY 

With respect to someone who's proven that he's knowledgeable here on BF-----

REALLY?

The OP (first post) describes a single wall rim, built wheel with a radial of drop 3mm over the span of 90 degrees (in two places).

Keeping in mind that single wall rims aren't very rigid in the first place, and that this is a comparatively gentle distortion (more ovalized than dented), combined with other clues, I reiterate that seems like much more of a wheel truing issue than a problem rim.

FWIW - It's his dough so I'm not invested in what this OP does. But I want others who might come across this thread to know that this is usually a wheel alignment issue, and not about a problem rim. Were we talking about a 1" deep double wall, semi-aero rim, my answer would be closer to yours.

urbanknight

If the wheel can be brought to decent true without going outside of proper spoke tension, fine. Otherwise, scrap the rim.

79pmooney

See my hightlights of OPs first post and my opening line. I simply addressed the OPs stated issues. If his rim is indeed bent, just truing won't make it right. I cannot see it so you may be right and the OP wrong. I'm making no assumptions, just answering a question and stating what we used to do in the '70s to rims like his.

FBinNY 

I think it boils down to opinions about what is correctable. IMO, a 3mm deflection over a span of 90 degrees with a comparatively flexible single wall rim is very correctable.

Of course, we never know all the details, like whether the error was originally much greater and this the best that could be achieved. And of course what's fixable, and how well depends on the skills of the mechanic. Something I, you or someone else can fix may be impossible to someone else. This is especially true with wheel building and alignment, which some degree of "touch" is as important as general skill and knowledge.

FWIW - I post here to help solve problems practically and economically. It's very easy to say "it's a bad part, replace it", but that often entails spending money unnecessarily, and the sin is compounded in things like wheelbuilding where there's a decent likelihood of ending up back in the same place. This is why, I offered a detailed outline of good practices, and suggested the OP loosen all spokes and start anew with this rim. If he takes that advice, the best case is that he saves the cost of new stuff, and maybe learns something. The worst case is that he "wastes" some time refining his skills and improves the odds of doing better next time. IMO- that beats using new parts in practice sessions.

Also note that the OP originally said it's a low end bike and he didn't want to spend much. Wouldn't that argue for making a serious, good faith effort to work with what he has?