The physics of properly stress relieving wheels?
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  1. #1
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    The physics of properly stress relieving wheels?

    Anyone have hard numbers on what tension needs to be achieved to properly relieve a new wheel, like how much momentary tension needs to be applied to the spokes to reach yield?

    Maybe more mental masturbation than useful, but Im kinda curious. Ive read between 50-100% increase in tension, so we're really trying to achieve (momentary) 150-200 kgf Seems like these numbers are going to approach rim damaging tension.

    Why doesnt rear wheel stress relieving occur after riding, from pedaling force?

  2. #2
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    Jobst Brandt says that it is a momentary raise in tension by roughly ~50% on the affected spokes.

    I would not worry about damaging rims/spokes during stress relief. Which way do you prefer, grabbing parallel spokes or putting your weight on opposing sides of the rim?

  3. #3
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    anyone else find the term "stress relieving" to be a bit of a misnomer?

    I like the phrase "getting rid of spoke wind-up".

    anywho, I've never damaged a rim while tweaking it. Though if you tweak a rim late in the build process (as in, when you think you're done), and it goes way out of true, tension in the spokes is likely too high.

    The point of "stress relieving" during the build process is to create a solid, single unit that won't come undone while riding. "Stress relieving" allows you to build a wheel uniform in tension before riding it. Sit on a bike in a department store...hear the pings? That's the wheel "stress relieving". Let's assume the tension on that wheel was proper when the bike was built at the store. Now that you've sat on it and heard the pings, the tension is no longer uniform.

  4. #4
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    It is more than just wind-up that you are getting out of the wheel, and yes.. stress is actually being relieved.

    When you build the wheel you put stress into the spokes, you have points on the spokes that are much closer to the yield point of the material. Stress relieving goes above the yield point, deforms them plastically, and allows them to take set with less "stress".

    An easier way of putting it would be that you force the spokes to take a shape when you lace the wheel, they will fight this if you do not bend or force them past that shape and allow them to naturally hold the final position.

  5. #5
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    I do the "put the wheel on the ground and push the hub into the carpet", but after some reading I dont think this does more than release windup. For my last set I also used a wooden rod to push the spokes at the cross, used a tool to bend them a little, and squeezed by hand.

    If 50% works, I think ill just settle on squeezing spokes.

  6. #6
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    I grab parallel spokes. It's not nice to the hub to side-load the bearings by resting the wheel on the floor and putting your weight on it. When I do feel the need to sideload the wheel, I have an old coffee table that has a hole in it big enough for the cassette side of a hub. This way I'm not putting any pressure on the bearings of the wheel when I lean on it.

    Spoke windup is not an issue for me. Right after lacing the wheel, I mark each spoke with a Sharpie so I know where they want to be when I'm done twisting them in the process of tightening the nipples.

    I don't care about the physics of it. What I do makes the wheels stay true for a long time.

    -Eric

  7. #7
    A wheelist
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    Quote Originally Posted by ergott
    I don't care about the physics of it. What I do makes the wheels stay true for a long time.
    -Eric
    OMG what a perfect statement Eric. Thanks for that. May I steal it and with your name attached, place it on my wheelbuilding site? What I do say on my site is this - "[here are] six techniques that achieve the above three steps of pre-stretching, removing wind-up and bedding. Each separate method achieves more than one effect so I will lump them all together under - Stress Relief."

    I'd rather let others argue what these steps do or what they are called. To make sure my wheels are the best they can possibly be I use every method I've ever found or heard of. I want the spoke bends to dig into the flanges as much as possible, I want the spokes to be as straight as possible, I want them to take the most direct route to the nipple as possible, to take any stretch or twist out of them and whatever else might happen in the first few yards, rides, months and years of use. All that stuff provides microns of movement; movement that will loosen spokes and allow nipples to possibly unscrew if it's not taken care of during the building process.

    I need to invent a word for this whole process that's never been used before so that no-one can interpret it.

    Your Sharpie trick for visible spoke twist is a fine one. Aero spokes like 'Rays are a joy to build with as, if the job is done right, there is no twist and, for the last set I re-trued, I purposely rode them up the street without doing any "stress relief" (or whatever anyone wants to call it) and there was no pinging. This kinda proved that there was no residual twist in those spokes. For any Newbs reading this and don't know what I mean - the bladed Sapim CX-Ray spokes can be held to prevent twist with a slotted tool. Sapim makes one.
    .

  8. #8
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    Quote Originally Posted by dmotoguy
    When you build the wheel you put stress into the spokes, you have points on the spokes that are much closer to the yield point of the material.
    That's true but the bend in the spokes also have variable residual stress from being formed. Exceeding the yield point creates a more even stress distribution.

  9. #9
    wheelbuilder
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    Quote Originally Posted by Mike T.
    OMG what a perfect statement Eric. Thanks for that. May I steal it and with your name attached, place it on my wheelbuilding site?
    Quote away;-)

    -Eric

  10. #10
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    Quote Originally Posted by ergott
    Quote away;-)
    -Eric
    Done & thanks!
    .

  11. #11
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    Ancient cultures in the rain forest would take drugs and dance naked all night to ensure the rain would come.. all they knew was that when they did that, it rained ;)

    Same idea. .you can waste a lot of time doing goofy wheel voodoo if you dont know the ultimate goal. A lot of wheelbuilders try to "destress" wheels by bending them against their legs with their arms. Ill be damned before im mashing a rim into my crotch, it just doesnt work same with the practice of walking on your rims, it puts way too much weight on your build.

    Nothing wrong with wanting to work smarter

  12. #12
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    Quote Originally Posted by TomH
    Ancient cultures in the rain forest would take drugs and dance naked all night to ensure the rain would come.. all they knew was that when they did that, it rained ;)

    Same idea. .you can waste a lot of time doing goofy wheel voodoo if you dont know the ultimate goal. A lot of wheelbuilders try to "destress" wheels by bending them against their legs with their arms. Ill be damned before im mashing a rim into my crotch, it just doesnt work same with the practice of walking on your rims, it puts way too much weight on your build.

    Nothing wrong with wanting to work smarter
    Not really. There are plenty of examples of wheels built like **** out there. Find the people that build good wheels and see what they do. It's not voo-doo. I just don't have a degree in metallurgy and leave those explanations to the ones that do.

    -Eric

  13. #13
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    One of the things I've learned over the years is to go past where you want the spoke/nipple/rim to end up and back off a hair. ie: tighten past the 'right' spot and loosen a smidge to get the twist outta the spoke.

    Untwist as you go so you don't hafta untwist later all at once.

    HTH

    M
    I've moved back to NoVA. PLEASE change the weather!

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