Is this rim no longer usable?

eeksll
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Is this rim no longer usable?

Postby eeksll » Sun Nov 04, 2018 8:05 pm

not entirely sure what happened to my wheel, but it was so far out of true on both side I couldn't actually figure out where center was on the truing stand.

I had a few issues in the past and one suggestion back then was to de-lace the wheel and see if it sits flat, in short it does not, it is a bout 3-4 mm off plane (see below).

Is this now toast?
if it is not worth while re-lacing, I figure I'll send it off to someone to get a wheel built around the hub.
However it is saveable/reuseable, I might give it a go myself.

Image

basicaly points (2) and (4) touch the table. points (1) and (3) are about 3-4mm off the table.
I have roatated it to make sure its not due to a non-flat table.
I have also flipped it and rotated it, so I am convinced the "high"spots are indeed high spots.

I have also taken multiple diameter measurements around the rim, and it appears to be round enough.

thanks in advance for any advice

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trailgumby
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Re: Is this rim no longer usable?

Postby trailgumby » Sun Nov 04, 2018 8:48 pm

I've recovered MTB rims with far worse warps than that. Like, seriously tacoed.

I had to make a manual attempt to partially straighten the rim first, which comprised a treated pine log mounted on a couple of bricks positioned underneath the rim at two and four, with my full body weight positioned at 1 and 3.

It took several attempts. You would be surprised how strong and springy alloy rims are. Eventually I replaced with new rims, but that was a couple of years later.

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ColinOldnCranky
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Re: Is this rim no longer usable?

Postby ColinOldnCranky » Mon Nov 05, 2018 1:22 pm

If you are talking of lacing in the old-school way, with spokes crossing 2 or 3 times over other opposing spokes then yes, that is what those lacing patterns are well designed for.

I don't know about those ore modern lacing patterns.
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Tamiya
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Re: Is this rim no longer usable?

Postby Tamiya » Mon Nov 05, 2018 1:50 pm

ColinOldnCranky wrote:If you are talking of lacing in the old-school way, with spokes crossing 2 or 3 times over other opposing spokes then yes, that is what those lacing patterns are well designed for.
I don't know about those ore modern lacing patterns.


does it make any difference? :? I'd have thought the width at hub should be enough triangulation to pull out any waviness even if the rim holes are all in the one line.

Rim holes on oldskool rims are slightly offset to their immediate neighbours to allow spokes crossing cleanly, right? (I'm scratching head looking at a wheel where the spokes are all bowed by their crossing... silly lacer must've started at wrong hole :shock: )

uart
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Re: Is this rim no longer usable?

Postby uart » Mon Nov 05, 2018 2:29 pm

eeksll wrote:Is this now toast?

As long as the 3 or 4 mm is gradual and not too abrupt then it should true up ok. I've salvaged rims way worse than that, and the higher the spoke count the easier it is to do. (That looks like 28 spokes is that right?)

When true it will have very slightly uneven spoke tensions to compensate for the internal stresses in the rim, but with a gradual 3 or 4 mm to pull that won't be very significant at all.

eeksll
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Re: Is this rim no longer usable?

Postby eeksll » Mon Nov 05, 2018 3:00 pm

yes its a 28 hole with 2 cross lacing and the curve is gradual. However, I am pretty much assuming the curve isn't normal.

what is the longevity outlook if it was re-laced with same spokes and rim?

In the past i have had a few broken spokes, both times they popped overnight. They where replaced with standard spokes (the rest are dt-swiss aerospoke of some sort). Even the current issue manifested itself overnight.

over time I have collected the correct spoke to replace them with, but never got around to doing it. Which is mainly why I am considering rebuilding it myself, although I do want a durable wheel and don't mind paying for that.


thanks all for your opinions so far, Ill have to sleep on it.

uart
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Re: Is this rim no longer usable?

Postby uart » Mon Nov 05, 2018 5:45 pm

eeksll wrote:yes its a 28 hole with 2 cross lacing and the curve is gradual. However, I am pretty much assuming the curve isn't normal.

what is the longevity outlook if it was re-laced with same spokes and rim?


I just measured two spare rims that I have here. The older of the two was out by a few mm similar to yours. The new one (almost unused) looks like it's true to within about a mm in it's unbuilt state.

Using a digital luggage scale, I measured to force to give a deflection of 3 or 4 mm like yours (at the 90 point while holding the 0 and 180 degree points firm to the table). It was 1.2 kgf for the old rim, and about 1.6 kgf for the newer rim. This is all the force imbalance that your spokes will have to overcome, and that will be shared by about 6 spokes.

It works out at about 0.3 kgf per spoke. This is absolutely negligible compared to the typical 100 kgf tension that the spokes will have anyway. Rims are never completely rigid, they are meant to flex under load by design. I think that your small residual deflection will have stuff all effect on the wheel - if built properly.

Your wheel might have just been badly built with wrong spoke tensions previously.

eeksll
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Re: Is this rim no longer usable?

Postby eeksll » Mon Nov 05, 2018 9:29 pm

thankyou very much uart, thats pretty decisive :mrgreen:

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Velo13
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Re: Is this rim no longer usable?

Postby Velo13 » Thu Nov 08, 2018 8:07 am

Build it as a front if you really want to give it a try. It will be good experience and will possibly work for a while, but over time spokes will start to break due to the uneven tension required to keep it straight (accelerated spoke fatigue of those at highest tensions).

No idea what happened, as that kind of taco is usually the result of a really big hit, on a wheel with too much tension in it. Very high tension is actually pretty likely - as many factory wheelsets are tensioned very high to 1) avoid spokes slackening and nipples unwinding during the (usually short) warranty period and 2) the factory only needs the wheels to last the warranty period (usually a year) so they don't care if the spokes are fatiguing quickly due to over tension.

Or, it could possibly just have been a product of not so good QC. Although that company is usually very good.

Please forgive my OCD from this point forward. It makes for good wheelbuilding, but (for some) dull conversation.

uart, did you perform your deflection measurements on built 28h rims? If so what gauge spokes and were they fully tensioned (i.e. completely finished wheels)? Were your forces applied at the same angle as a pulling spoke would?

In my experience, the amount of force required to migrate an unbent rim 2mm each way is considerable - once you factor in the forces of all the other spokes in the system. This lateral pulling force on the rim could be multiplied further on a rim that's actually bent away from where you want it to be (i.e. working against the resting state of the rim).

This will have to happen on 2 zones on one side, and 2 on the other. For every spoke that requires additional tension, there is a spoke working against it (but to lesser tension than if the rim was straight in the first place). I'd expect the tension difference to be at least 20-30% (on the same side of the wheel) between the higher tension pulling spokes, and the slacker spokes 90/270deg from them.

Considering this rim will have a max reliable tension in the 120kgf vicinity (on the driveside only of a rear), that means that the slack spokes on the offside (assuming NDS spokes have a tension of 65% of the DS) may need to have tension as low as 55kgf. Far too low for a reliable wheel. NDS nipples will either unwind, the constant shock loading of less tensioned NDS spokes fully detensioning and retensioning will see dramatically reduced life (broken spokes at the bend), and those 4-8 DS spokes at 120kgf will see the majority of cyclic stress loads and fail early (usually in the middle).

All rims I order are checked on arrival and must be within +/- 0.5mm laterally to be accepted. Straight rims mean even tension, which means reliable long lasting wheels.

Phew.

uart
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Re: Is this rim no longer usable?

Postby uart » Thu Nov 08, 2018 11:56 am

Thanks for that Velo13. You're totally right that I didn't take into account the spoke pull angle. I realized this soon after posting and was going to update with that info, but forgot to. :o

I also agree with you about this not being ideal, and best to make it a front. However I still disagree about the amount of imbalance that this will cause.

Taking account of the spoke pull angle (about 1 in 8 on a front wheel) and taking an approx sinusoidal distribution in tension across the 5 closest spokes I get about 25 percent of the total required restoring force in the closest spoke. This peak imbalance will then be about 0.25*8*1.6 kgf, which comes to about 3.2 kgf.

This means that on a front wheel it will only result in about 4 percent imbalance, which really should be fine. I mean, a dished rear wheel always has a lot more imbalance than that at the best of times.

eeksll
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Re: Is this rim no longer usable?

Postby eeksll » Thu Nov 08, 2018 8:05 pm

Just an update, I decided to take the good part of the wheel (the hub) and get a wheel built around it. I had already decided to go ahead with Velo13 (he had built a wheel for me before) and pointed him to this thread.

I really only have the 1 wheelset for the road bike (my spare wheel is a 10 speed wheel with a 11 speed sram cassette on it, my bike is a campagnolo setup) this was a major factor in choosing to get it built properly.

ie less than ideal rim, with used spokes and less than ideal builder (me) most likely = dodgy wheel.

I ordered a tiagra 11 speed hub to try build what I have up, I did that before reading velo13 post above. If I had read that first I would probably have not got the tiagra hub to try the build ... however I am in it now :!:

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