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bented rim, truing wont fix...

Old 03-08-16, 08:43 AM
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bented rim, truing wont fix...

the bike fell off my car when I go thru a bump that I wasn't paying attention to. the rim is bented only on a concentrated area. I tried to adjust the tension of the spoke but it didn't work. I also tried to put my body weight (85kg) on the rim to force bend it back, it work a little bit but still its out of true. This is a 20 year old bianchi, it wont worth too much now so I don't want to buy some fancy rim but I don't want to buy some cheap rim either.... so I wonder if there is other way to fix the rim....
thanks
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Old 03-08-16, 08:52 AM
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There are three different ways a rim can go out of true: The spoke tension can become uneven, the rim can be dented, and the rim can be bent. Only the first can usually be fixed by adjusting spoke tension. Dents can sometimes be repaired to satisfaction but will likely never be perfect. Bent rims can sometimes be repaird to make them ridable again, but the rim will likely never be perfect. At best the rim will be straight but spoke tension will be wildly uneven. A new rear wheel will cost starting between $70 and $100 (and up to thousands of dollars if you want something fancy, a bit less if you need a front wheel), but used wheels are also often available. Is yours a front or rear wheel, and if it is rear, what sort of gears are on it?
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Old 03-08-16, 10:56 AM
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There may Be, but you may not want to watch some one doing it.
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Old 03-08-16, 11:58 AM
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I'd say buy a used wheel to replace the damaged one. Doesnt have to be 'fancy' but you should be able to get something equal to what was on the bike for not too much money. It's the best way to go imo if the original rim is badly damaged.
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Old 03-08-16, 03:15 PM
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If you have the time to spare, I've frequently been successful in unlacing rims, bending them flat, then relacing.
Takes some time, but if you'd only have spent it watching tv otherwise, no big deal.
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Old 03-08-16, 05:36 PM
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"bented rim"? Front or back? What size wheel? What exact model? How many speeds if it is a back wheel? Bianchi has made some great bikes that are well work repairing. Without knowing more any answers you get are just guesses
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Old 03-08-16, 05:37 PM
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As long as the rim's section isn't buckled or otherwise damage, the rim can be straightened. This is straight out brute force, hand/eye skill work, but a someon with decent hands can get the rim very close to perfect, with spoke work later making it into a true wheel.

Basically, you need to slacken the spokes so you see the true nature of the rim, and to give you the ability to work the rim without fighting the spokes. Then "read" the bend to see where it's actually bent, and find a way to bend it back. Here's where Archimedes had it right. You'll need to put a fulcrum in the critical area and lever it back into flat.

Depending on the bend and options at hand, I've bent rims against my knee, placed something on the floor and stood on them, trapped them in a grating and bent, used broom sticks levered against the hub and/or each other, and other similar methods. It's not as much about how you lever the rim back home, as placing the fulcrum in the right place, and applying correct force.

Unless you have a good eye, you'll want some reference to check the rim. Unfortunately, the hub will prevent the obvious method of laying it on the floor. So her again some thinking is called for. The easiest way is to use a new and known to be flat rim for comparison. Or you can make a circle of a bunch or identical soup cans and use the tops as your reference. If you own a dishing gauge, that can also be used but takes some added skill in this application.

My point is, that you are now ready to toss the rim, so this is a "nothing to lose" learning opportunity. (unless you're on a tour far from an available replacement).
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Old 03-08-16, 05:55 PM
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Originally Posted by fietsbob
There may Be, but you may not want to watch some one doing it.
Yup! THe way to "fix" that rim is to loosen the spokes on the side of the bend for the extent of the bend, then slam the wheel down, tire on and inflated, on a concrete step. With the appropriate slam, that area of the rim will now be a little off to the other side. Tighten those loosened spokes and you are god to go.

Do this only with low grade, low alloy (steel or aluminum) wheels. DO NOT do this with high quality rims of strong metals. The cheap stuff will bend. The good stuff will crack and break, now or when you are riding it later.

I worked with a mechanic who really had the touch for bending metals. (Both"truing" wheels and straightening frames.) We would send the customer off and tell him to come back in four hours. 5 minutes later, the slam was done and the mechanic was tweaking the last few spokes. Hours later, the customer would come back, be amazed at how his wheel turned out, pay us and go away happy.

Ben
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Old 03-08-16, 07:59 PM
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If it can't be fixed, you may be able to find a replacement rim with the same ERD (effective rim diameter) so that you can use the existing spokes.

The "best" solution depends on how bad it's damaged, budget, condition of spokes, rim availability etc...
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Old 03-09-16, 09:36 AM
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Thanks all for your input. Its a 700c rear wheel. Its a mavic 2xx I forgot rim.... 7 speed cassette with probably the first gen. sti dura ace. That's why I don't want to just throw the rim away and get a replacement... Things are old but are very nice parts back then. Its like 6cm length along the rim is bent. And its about 3mm out of center. I tried to put two block at the a few cm away from each end of the bented area and then jump on the bented area. It helped to get to the current 3mm out of center but wont go further. And adjusting the spoke wont fix it either. This is good enough the brake wont touch the rim when I ride but when I brake, I can feel a bump once the brake hit the bented area.... I guess most of you suggest just try use force to bend it back. do you guess have any suggestion what tool i can use to put more force on it? apparently my weight is not enough
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Old 03-09-16, 10:08 PM
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Originally Posted by hj630
Thanks all for your input. Its a 700c rear wheel. Its a mavic 2xx I forgot rim.... 7 speed cassette with probably the first gen. sti dura ace. That's why I don't want to just throw the rim away and get a replacement... Things are old but are very nice parts back then. Its like 6cm length along the rim is bent. And its about 3mm out of center. I tried to put two block at the a few cm away from each end of the bented area and then jump on the bented area. It helped to get to the current 3mm out of center but wont go further. And adjusting the spoke wont fix it either. This is good enough the brake wont touch the rim when I ride but when I brake, I can feel a bump once the brake hit the bented area.... I guess most of you suggest just try use force to bend it back. do you guess have any suggestion what tool i can use to put more force on it? apparently my weight is not enough
The spokes need to be loose so that the rim has room to unbend. It needs to go beyond the final point, then spring back.

You may also have a small bulge in the rim causing brake grab. You might be able to use Channel-Lock pliers to carefully squeeze in the bulges. If the bulge is only on oe side, use a block of wood to spread the force out on the good side.

Sounds like you will have to settle for "good enough" or consider replacing the rim.
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Old 03-10-16, 01:06 AM
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Are you talking about a sidewall flare, or the whole rim being bent?
Such a local damage, 60 x 3 mm, sounds more like a flared sidewall than a bent rim.

And apart from requiring re-bending of metal to straighten, they're completely different animals.
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Old 03-10-16, 01:21 AM
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Originally Posted by hj630
Thanks all for your input. Its a 700c rear wheel. Its a mavic 2xx I forgot rim.... 7 speed cassette with probably the first gen. sti dura ace. That's why I don't want to just throw the rim away and get a replacement... Things are old but are very nice parts back then. Its like 6cm length along the rim is bent. And its about 3mm out of center. I tried to put two block at the a few cm away from each end of the bented area and then jump on the bented area. It helped to get to the current 3mm out of center but wont go further. And adjusting the spoke wont fix it either. This is good enough the brake wont touch the rim when I ride but when I brake, I can feel a bump once the brake hit the bented area.... I guess most of you suggest just try use force to bend it back. do you guess have any suggestion what tool i can use to put more force on it? apparently my weight is not enough
Typically the area work hardens and the edges of the bend will be funky. If you can get the center part on center and the edges are manageable, that may well be as good as you can do. If you have a calipers gauge, you might see how much sidewall you have. If there is still plenty left, you could dress the bumps with a file and improve the braking. Barring that, perhaps some creative squeezing with vise grips and small wooden blocks might help. I can't see your rim, so I am just throwing out ideas.

Ben
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Old 03-10-16, 02:32 AM
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It may be worthwhile to have a new rim "laced up" with your present hub, especially if it is Italian made vs Japanese/Taiwanese/Chinese. Have shop look at it

If it has a flat spot without much sideways wobble, some shops have tool that can pull the flat spot out.
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