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rim collapse while tensioning

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rim collapse while tensioning

Old 01-30-17, 10:45 PM
  #1  
joedab
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rim collapse while tensioning

so I destroyed a wheel recently during truing at the stage after tensioning the spokes, when the wheel is placed flat on the ground contacting the hub axle and the rim is pressed downward to de-stress the spokes so it doesn't come out of true. I've done this many times before with proper effect, but on this particular wheel with the drive-side up, the rim buckled and the hub shifted way out of place toward the drive-side bending the spokes opposing and stretching the others facing up. Right after noticing what happened, I snapped the wheel back into shape, and yet the wheel was afterward untruable.

I have done this with many other wheels prior, but I am starting to think this might actually be an antiquated technique, and that it would be better to simply oil the rim/nipple, nipple/spoke contacts before tensioning and then just fine-tune the wheel after a ride. Has anyone had a similar mishap? I did not apply a noticeably stronger force downward, yet this was a single-walled rim and the lightest of wheels I've worked with.

The wheel without a tire or skewer weighs in at 1188g while any other rear wheel I weigh hovers around 1400g average. I figured this is due to a single-walled rim having less material and therefore being lighter, and yet I asked at a LBS if racers still use single-walled in favor of double-walled rims for this reason and they seemed to think double-walled rims are always favored. Is strength more important than weight in this case?
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Old 01-30-17, 10:53 PM
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The technique you used has the risk of the consequences you suffered. There's a point of no return when rims are deflected sideways, and the wheel moves to a lower energy condition. The likelihood of this happening depends on where exactly you're pressing with respect to the cross pattern, and is also far more likely when you do this with the drive side down because the rim starts out so close to the flange plane.

The technique is related to more than simply allowing twisted spokes to relax. It also over stresses the spokes and stress relieves them.

I rarely use this method anymore, preferring to bend the wheel over my knee where I feel I have better control. I also use other methods to over tension spokes and st the elbows which is what I feel is the most important part of the final settling process.
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Old 01-31-17, 12:22 AM
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I've never used anything like these methods. I just squeeze together hard the pairs of spokes as I rotate the wheel.

It has been extremely rare that any of the wheels I have built have gone out of true on the first ride or the 10,000th kilometre... single or double walled. No spoke prep is used, either.
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Old 01-31-17, 05:42 AM
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I've had one wheel potato chip on me when stressing as the OP described and thereafter only squeezed parallel spoke pairs. No problem since.
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Old 01-31-17, 07:28 AM
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Here's another vote for squeezing parallel spokes. I think I picked that up from Jobst Brandt.
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Old 01-31-17, 07:41 AM
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+1 for squeezing spokes instead of stressing the whole wheel.

I squeeze a pair of spokes on top and bottom (i.e. 4 at a time) when the wheel is in the truing stand. Very light squeeze for the first rotation then a little harder for the second. Fine-tune re-true if needed and I'm done.
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Old 01-31-17, 07:54 AM
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Squeezing pairs, or sets of four spokes serves a different purpose than flexing the rim the way the OP did.

Rim flexing is about creating slack in some spokes to detect and/or correct spoke windup. However it's done, it's an important step, especially when building with thin section swaged spokes. Every skilled builder I know uses a variant of this technique, and the OP's bad luck doesn't invalidate the method. However, it's a reminder of the need to appreciate the risk, and exercise due care.
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Old 01-31-17, 08:51 AM
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If one notes the amount of spoke wind up during each spoke nipple's turning then one unwinds said spoke that amount the result is that each spoke will have nearly no wind up when done. Since releasing wound up spokes is the usual reason to stress the entire wheel/rim 9as opposed to squeezing pairs of spokes which set the elbow and nipples in their holes/seats) if one does the unwinding method one can avoid the need of a rim taco potential distressing step.


Another way to reduce the taco chance is to place the wheel flat against the work bench top with a section of the rim overlapping the top's edge, axle on the top. Then press away. This reduces the leverages and because you're using more arm then upper body the chance of going too far is reduced. Andy.
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Old 01-31-17, 10:07 AM
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I just place the wheel upright on a carpet and press on it with the heels of my hands. I wear work gloves while doing this and press hard enough to almost lift myself. I then rotate the wheel a bit and do it again. I continue for about 2 full revolutions. This method always worked for me.
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Old 01-31-17, 10:37 AM
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Squeezing parallel spokes catches about 80-90% of spoke windup, IME, along with a low-risk way of stress relieving the spokes.
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Old 01-31-17, 11:25 AM
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Originally Posted by FBinNY View Post
The technique you used has the risk of the consequences you suffered.
So you are saying it wasn't Aliens?
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Old 01-31-17, 11:43 AM
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Originally Posted by wheelreason View Post
So you are saying it wasn't Aliens?
Not even illegal aliens.
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Old 01-31-17, 03:46 PM
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Originally Posted by FBinNY View Post
Not even illegal aliens.
There's a wall for that.
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Old 01-31-17, 04:36 PM
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This happened to me twice when using the squeeze-parallel-pairs method. Same hub, same model rim, different cross pattern. It was an Atom tandem hub (with gigantic flanges), Weinmann concave rim, 48 spokes. First, I laced it 5-cross. Wham. I distrusted the rim so I used another new one and laced it 4-cross. Wham. I didn't have the length required for 3-cross, so I laced it 2-cross. No problems, and the wheel lasted a long time. I'm not sure what happened.

I don't eliminate spoke wind-up by pressing the rim over the hub in the way described above. Instead, whenever I tighten a spoke, I overtighten it a quarter turn and then back off a quarter turn. It's not precise, but it works well enough. And I still use the squeeze-parallel-spokes method for stress relief.
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Old 01-31-17, 05:44 PM
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FWIW, 'flimsy' rims should be treated gently. I have a couple Campy Omega tubular rims that I would NEVER use the method you mentioned on them.
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Old 01-31-17, 07:46 PM
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Sissies.

Stand on that wheel, even better if you can jump on it.

I do the same thing as the OP, just have to be careful if the wheel has a lot of dish, or less than 32 spokes.

I've got girly hands so the squeezing spokes method rarely works for me.
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Old 01-31-17, 08:04 PM
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Originally Posted by SHBR View Post
Sissies.

Stand on that wheel, even better if you can jump on it.
Funny you say that.

BITD - one of the best wheel builders I knew, a big Irishman named Marty, had an amazing technique. He'd lay the wheel on the floor, and "walk the rim", holding one side down and pressing the other, working his way around the wheel, then flip it and repeat.

To my knowledge, he never collapsed one this way, even the very light rims and spokes we were using back then.

--------------------------

The nearest I ever got to this was when I was teaching a wheel building course, and someone expressed concern about radial wheels.

To allay his concerns, I took the front wheel (radial) off my track bike, put it on the floor, stood on it like a teeterboard and balanced myself on the axle. I was doing fine until I got carried away and jumped a bit. The wheel held up, and I'm still riding it, bent flange and all.
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Old 02-01-17, 12:35 AM
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I'd rather destroy a wheel at home than out on the road, however there isn't much you can do if a motorcycle or an e-bike tags your back wheel while in an intersection or while stopped at a light.

Phone zombies are a real menace, not only just to themselves, but to every other road user.

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Old 02-03-17, 10:20 PM
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I know flexing the wheel is to release spoke twist after truing, but squeezing parallel spokes is mainly for seating new spokes? I always tighten spokes 1/4 turn too much then back and do the same while loosening if the spokes are tight or corroded, but still I find myself going back to the method of flexing the wheel .. it gives me the feeling of being complete. I am definitely more careful since and have noticed that the wheel is actually more prone to collapse with the drive side up, which is contrary to intuition and as suggested in the second post. Anyone have ideas why this might be?
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Old 02-03-17, 10:25 PM
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Originally Posted by joedab View Post
.... I am definitely more careful since and have noticed that the wheel is actually more prone to collapse with the drive side up, which is contrary to intuition and as suggested in the second post. Anyone have ideas why this might be?
It's a question of trade offs between two effects. The rim is easier to deflect to the left because the right spokes have a lousy bracing angle. However, the distance to the point of failure is shorter on the right side, so greater care need be exercised in that direction.

So, choose your poison ---- move too far because it's easier, or work harder to move a much shorter distance, working with less margin for error.

BTW - my bias against moving to the right may be because I use lighter spokes on the left, so moving right isn't harder than moving left, and I'd rather have the margin.
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Old 02-04-17, 05:27 AM
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I haven't bothered stressing a wheel during a build for decades. Instead, I (i) install the first head-in spoke in the hub; (ii) aiming the spoke at the point where it will be inserted into the rim, bend the spoke inward over the hub flange a bit past its final angle to the rim; (iii) thread the nipple onto the spoke; (iv) repeat for the next head-in spoke.

Stressing the wheel does the same thing: it adds a slight bend to each head-in spoke where it passes over the hub flange (and does little or nothing to the head-out spokes).

But bending the head-in spokes one at a time at the beginning of the build is easier to do and safer than the brute-force wheel-stressing technique.

The wheel comes up to tension faster, too.

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Old 02-04-17, 08:29 AM
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I don't think I've ever had a new rim get close to tacoing. Back in the bad old days when I worked at a bike shop where we couldn't turn down paying work, I trued many wheels that were pretty close. I always felt the spokes start to loosen and stopped pushing before that happened though. On those, I would usually move the rim out of center a little to even up the tension.
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Old 02-04-17, 09:14 AM
  #23  
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Originally Posted by gearbasher View Post
I just place the wheel upright on a carpet and press on it with the heels of my hands. I wear work gloves while doing this and press hard enough to almost lift myself. I then rotate the wheel a bit and do it again. I continue for about 2 full revolutions. This method always worked for me.
I saw a variant of this - the guy lifted the wheel and let it fall on a piece of wood. I didn't like it, but he said it worked for him.
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