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Bent rim front or rear?

Old 01-09-22, 01:58 PM
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densolo
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Bent rim front or rear?

Hi all,

I picked up a vintage Motobecane a few months back with a bent rim in the rear wheel. The rear wheel was disassembled and I'm waiting for parts to rebuild it. In the meantime I've disassembled the front wheel to give it a good clean. Now that I have both wheels disassembled I was thinking, where should I place the good rim (on the front or in the rear)?

My first thought was that the rear wheel carried much of the load and therefore the better rim would work best in the rear. However, on second thought, when riding downhill for instance, I figure having a good/true wheel on the front is paramount (a slight wobble in the rear is better than having it in the front, especially going downhill).

What do think?
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Old 01-09-22, 02:09 PM
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I think that while the wheels are disassembled you should try and fix the deformity then it won't matter. A lot of rim damage can be mitigated with simple tools. You can gauge your progress by comparing to the good rim side by side.
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Old 01-09-22, 02:14 PM
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A wobble on either wheel can be problematic for different reasons, depending on how bad. Rims are consumable items you would have replace after enough use anyway, so it’s not as though they are permanent.

The thing is — if you can build wheels, then taking care of a wobble should be a piece of cake, and there is no reason you can’t have a wobble-free wheel on both front and back.
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Old 01-09-22, 02:15 PM
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Rear.
What hub and spokes are you using? Probably better off finding another used wheelset on Kiji or whatever. If your fixing the nomade, upgrade to alloy rims and shimano hubs.
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Old 01-09-22, 02:23 PM
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Truer rim should be in front for the same reason a tire with less tread wear should be in front. More stability.
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Old 01-09-22, 03:19 PM
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The front rim brake does most of the work, so the front rim should be perfectly true.

I've built wheels before with less than perfect rims, and I learned my lesson. It's just not worth it. Sun m13ii rims are inexpensive.
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Old 01-09-22, 03:54 PM
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If you are going to build your rim(s), check for flatness by placing on a flat surface, coffee table, kitchen island, something you know is going to be flat. If it is only slightly bowed, you can bend it back with some practice. Before you do that you should check for roundness before you unlace.
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Old 01-09-22, 04:46 PM
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I'd get a replacement rim.
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Old 01-09-22, 04:53 PM
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Thanks for all your replies!

I'm actually new to bicycle repair. So I've rebuilt the rear wheel once (with some transplanted spokes) but the spokes were 2.0mm vs 1.8mm (original). So I disassembled again, and ordered some 1.8mm spokes.
What I learned (from the rebuild) is that lateral truing is off by 1~2mm on both sides (it wobbles slightly). But also, I think there's one section that needs radial truing.

I actually picked up an extra set of wheels recently (visit to Montreal). Rigida 27x1-1/4. But they are 4-cross laced (spokes are 307mm length), high-flange hubs (noname). The rear wheel has english threading (and I need french).
But also, the front hub is 100mm o.l.d which I learned takes a 3/8 inch axle. My Motobecane front dropouts takes a 5/16 inch axle.

I intended to use the extra rims to build new wheels. But I actually want to save the originals and rebuild them (and also buy new hubs for the extra rims). For the learning experience (as well as a set of backup wheels).

So going back to your replies @Classtime says put the good rim on the rear, while @nlerner says put the good rim on the front. I suppose it doesn't make a huge difference if the wobble is only slight?
Thanks.

Note:
Original front hub is Weco high flange on Rigida rim.
Original rear hub is Atom low flange on Rigida rim.
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Old 01-09-22, 06:23 PM
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lateral and radial adjustment I think should happen concurrently. Think in pairs of spokes to control radial trueness.
if the wheel is 6-7 speed, the drive side spokes in my opinion should be 2mm shorter on the drive side.
use one of the spoke calculators, when the wheel is done the spokes should fill the nipples to the slot or to the end on the nipple.
some rims will allow you to go a bit longer as the nipple termination will not be in the tube cavity.
I do not like going shorter as I do not want an unsupported nipple carrying the full tension load.
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Old 01-09-22, 06:30 PM
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I've built wheels before with less than perfect rims, and I learned my lesson. It's just not worth it. Sun m13ii rims are inexpensive.
I have built lots of wheel sets and I agree 100% with the above comment. Used stainless steel spokes = OK if in good shape. Used/rebuilt hubs = OK. Used bent rims, not a chance. Even less than not a chance if they are alloy.
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Old 01-09-22, 06:51 PM
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densolo
oops. I intended to indicate bad rim on rear: title--bent rim front or rear. I was focusing on the bad rim. Seems like you found yourself a new hobby👍 Don't go bombing down the mountainside right away on your new wheels. Start on smaller hills without traffic😉 AND of course we want to see this bike when you get 10 posts.
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Old 01-09-22, 10:39 PM
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Originally Posted by repechage View Post
lateral and radial adjustment I think should happen concurrently. Think in pairs of spokes to control radial trueness.
if the wheel is 6-7 speed, the drive side spokes in my opinion should be 2mm shorter on the drive side.
use one of the spoke calculators, when the wheel is done the spokes should fill the nipples to the slot or to the end on the nipple.
some rims will allow you to go a bit longer as the nipple termination will not be in the tube cavity.
I do not like going shorter as I do not want an unsupported nipple carrying the full tension load.
Thanks for tip repechage , I didn't know you could radial true a rim through spoke adjustments. I'll have to check out some more youtube videos.
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Old 01-09-22, 10:47 PM
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Originally Posted by Classtime View Post
densolo
oops. I intended to indicate bad rim on rear: title--bent rim front or rear. I was focusing on the bad rim. Seems like you found yourself a new hobby👍 Don't go bombing down the mountainside right away on your new wheels. Start on smaller hills without traffic😉 AND of course we want to see this bike when you get 10 posts.
Thanks Classtime , I'll leave the bent rim for the rear wheel then

I'm loving the new hobby. It's not too complicated, but difficult enough. A perfect winter project.
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Old 01-10-22, 06:52 AM
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@densolo - if you really want to get close to understanding rim distortion during the build, get a spoke tension meter. My experience with wheel building is limited and spans over 40+ years. I learned a lot from plotting tension on a spider chart to understand the distribution and the impact on the rim trueness in every direction. Once you get it down, it is not that difficult except when dealing with slightly bent rims.

Like some and unlike others, I like to understand the mechanics of things and don't just throw away a part because it presents too much of a challenge. I don't know my limits unless an attempt is made. Sometimes it works out, other times the results are a new lesson or the limit is reached. Rigida 1320 is the one of the most challenging rims to true and push toward replacement. Suns are a good choice but do not have the same profile.

In addition, consider butted spokes of 2/1.8 variety, Big controversy on that topic too but many believe they are a better/best choice over straight ga. spokes.

Here is an example of going the distance, flat spot in the rim fixed. X marks the spot of flatness and the vertical lines the transition points.
P1030737 on Flickr
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Old 01-10-22, 02:10 PM
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Thanks SJX426 for the image! Flat-spots. That's the term used. I saw a video (Oz Cycle) on Youtube where he built a tool to deal with flat-spots.

But I like your solution better because it uses tools that are more readily available.

I have modest goals for trying to correct the bent rim. I'll try my best and see what happens.
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Old 01-10-22, 02:44 PM
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I took it upon myself to bend two rims back into shape. It was fun for a retired guy with allot of tools and time and I did get them back into shape.

But I really should have just bought new rims...
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