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Truing a wheel by a LBS

Old 12-24-09, 12:39 PM
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I've actually tested the spoke-tension - using an FSA tension-meter - without tire on, and with tire on and inflated. In most cases, there was a notable drop of spoke-tension after mounting and inflating said tire. And the true quite often changes as well. As a chemist - I know how to make accurate measurements of such animals. If I didn't, I'd likely be in the ionosphere today.

As for the person who brought in a wheel, with tire and tube on which had a slow leak, and got it back with a new inner-tube: The mechanic likely didn't know there was a slow leak and may have thought he/she had pinched your tube on remounting it. He/she gave you the benefit of the doubt. And a new inner-tube. Sign of a decent shop.
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Old 12-24-09, 01:21 PM
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Originally Posted by noglider
Thanks Tom. This is what I was looking for.

BTW, the WAG4 seems to be the right dish too for me since it works on 20" wheels.

Kam
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Old 12-24-09, 04:13 PM
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Operator is correct on this one, at least when dealing with a high pressure road wheel. Normal riding pressure can change the spoke tension, wheel dish and sometimes lateral true on rear wheels. I've tested this several times and the difference from a bare rim to 115 psi can chainge spoke tension 5%. These tests have been on Open Pro and DT Swiss RR 1.1 rims. Wheel dish has been effected by about 1/2 mm. May not seem like much but it does it every time so I've learned to make my final dishing and truing with the tires mounted.

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Old 12-24-09, 04:45 PM
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What dishing tool touches the rim and not the tires?
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Old 12-24-09, 05:01 PM
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Park

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Old 12-24-09, 05:51 PM
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Ooh, that's hot!
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Old 12-24-09, 06:28 PM
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Ha! I just bought one of those but haven't used it yet. I wanted to by a tension gage, too, but the $100 price for the pair put me off - way off.

Too bad no one rents the gages. It'd be nice to know (quantitatively) that you are in the right ballpark in tension rather than just relying on the "sproing!".

I used to make my final tensioning and dishing adjustments on the bike with the tires installed and inflated. I guess I just got lucky doing it that way.

Last edited by Mike Mills; 12-24-09 at 06:55 PM.
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Old 12-24-09, 10:01 PM
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Originally Posted by mas-az
I fear you know not what you say, Operator regardless of your 25,000+ posts. You cannot put enough pressure into a tire to affect the wheel without blowing the tire or tube or both. Pure BS.
+1 if air pressure in a tire is enough to mess the true significantly on a rim.. i would be more worried about the integrity of the wheel or the braking surface thickness or something.., second, ive never seen this happen on any rim. ever.
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Old 12-24-09, 11:52 PM
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It happens. It doesn't compromise the integrity, but it can push it out of true a bit. Not much, but a bit.

Remember, a few of us have been or are currently bike mechanics. We've seen a lot of bikes, and our experience has shown things you haven't seen yet. Not BS.
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Old 12-25-09, 11:41 AM
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Originally Posted by noglider
Remember, a few of us have been or are currently bike mechanics. We've seen a lot of bikes, and our experience has shown things you haven't seen yet. Not BS.
And your experience is greatly appreciated. That response was generated because Operator was replying as the spokesperson for the bike mechanic community saying that you all don't prefer to have the tyre/tire removed. That was the BS I was talking about.
Had Operator said "I prefer....Because..." I would not have responded. As I see it Operator had to take and twist the issue with edge cases so he could mark his territory on this forum.
Doesn't matter which forum you got to, bicycles, Smith & Wesson et al you'll find the alpha wolves lurking waiting for fresh meat to chew into and spit out. And the pack hierarchy can generally be determined by the number of posts an individual has made.

I hope everyone had a great Holiday today.
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Old 12-25-09, 12:13 PM
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True, but watcha gonna do? He is who he is. Don't like his manners? You don't have to, I guess. I don't, either, but he's clearly a good mechanic, and I learn from him, and we all can, too.

I still prefer to true wheels without a tire, but I find it interesting that he likes the tire on his wheels.

Merry Christmas, everyone!
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Old 12-25-09, 12:33 PM
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The tire and tube thingy...

I like having the customer bring 'em in and on either to me or the shops that I do wheels for.

1. Keeps fallover or bump damage from happening...you'd be amazed at how often bare wheels on the ground fall over and hanging bare wheels get dinged by other bare wheels.
2. I'll do my truing and build bare...not a bother really to take 'em off...big frickin deal.
3. When done putting the tire and tube back on provides:

- Ultimate test of overtension.
- Further test of stress relief.

...should a nipple or two do the "tink" thingy...there's a chance to do a "click" here and there before the customer picks it up.

=8-)
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Old 12-25-09, 12:49 PM
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Originally Posted by rs1101
+1 if air pressure in a tire is enough to mess the true significantly on a rim.. i would be more worried about the integrity of the wheel or the braking surface thickness or something.., second, ive never seen this happen on any rim. ever.
If you've built enough wheels and use a tensionmeter to measure spoke-tension before and after mounting a tyre & pumping it up, you WILL learn over the course of building hundreds of wheelsets that the air-pressure DOES push inwards on the rim and decrease the spoke-tension. Typically about -5-10% based upon the rim-stiffness and actual spoke-tension. Depending upon how true the unlaced bare rim is and the amount of dish, this change in spoke-tension will throw the wheel out of spec.
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Old 12-25-09, 01:48 PM
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mrrabbit thanks. A response that makes it clear why it doesn't make any difference. I'm sure there is one or two of us that have learned a thing or two from it. I did for sure.
And you did it without kicking my butt. Kind of like something Sheldon Brown would do.
I have learned to beware the ..er. Because there is always someone mightier, richer, smarter, nastier, meaner, and greater then I'll ever be. And I have said this before, experience is the sum of your failures and I fail a lot.
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Old 12-25-09, 06:25 PM
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I'm prolly not alone in being quite surprised by this...

So, in order for the spoke tension to be reduced by as much as 5% (!), the rim - which is designed to resist forces in the direction of its centre more than anything else - obviously has to be significantly compressed to a smaller diameter...

Weird. I would not have guessed; being under the impression that it takes a lot more force than that to compress a solid...

I wonder how much decrease in diameter we're talking about here? It should be measurable... half a millimetre or something?
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Old 12-25-09, 06:52 PM
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Originally Posted by Kimmo
I'm prolly not alone in being quite surprised by this...

So, in order for the spoke tension to be reduced by as much as 5% (!), the rim - which is designed to resist forces in the direction of its centre more than anything else - obviously has to be significantly compressed to a smaller diameter...

Weird. I would not have guessed; being under the impression that it takes a lot more force than that to compress a solid...




I wonder how much decrease in diameter we're talking about here? It should be measurable... half a millimetre or something?
If you'd care to splurge and find out for sure - which I am - this is arguably the best. And not the most expensive:

https://www.biketoolsetc.com/index.cg...item_id=FS-STM

It's what I use. One-handed & easy.
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Old 12-25-09, 06:57 PM
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Seems a lovely bit of kit, and I'd like to have one, but at that price it'll be a while before it gets to the top of my pile of priorities...
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Old 12-25-09, 10:15 PM
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Originally Posted by Kimmo
So, in order for the spoke tension to be reduced by as much as 5% (!), the rim - which is designed to resist forces in the direction of its centre more than anything else - obviously has to be significantly compressed to a smaller diameter...
Not significant at all. Here's how to find your answer:

1. look up Young's Modulus for 6061 aluminium
2. look up Young's Modulus for 18-8 stainless steel
3. calculate cross-sectional area of a 2.0mm SS spoke
4. calculate the amount of elongation of a 290mm spoke at 1000-1300 N.
5. calculate the decrease in elongation needed to reduce tension by 5-10%

Also what can you conclude by comparing #1 versus #2???

Last edited by DannoXYZ; 12-26-09 at 02:20 PM.
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Old 12-26-09, 11:39 AM
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DannoXYZ, there you go again, injecting your superior knowledge and understanding to debunk all of our misperceptions.
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Old 12-26-09, 05:47 PM
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Originally Posted by noglider
DannoXYZ, there you go again, injecting your superior knowledge and understanding to debunk all of our misperceptions.
So I guess you, myself, Al1943, Operator and company are no longer needed here, right?

...we'll just let Danno do all the educating while we actually build the wheels and rake in the dough!

Great! Sounds like a deal!

=8-)
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Old 12-26-09, 06:42 PM
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Is this a new trend I smell? Using a 40-foot stage-cane to yank people off their pedestals? Be careful - they may come for you one day!
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Old 12-26-09, 09:57 PM
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Originally Posted by DannoXYZ
1. look up Young's Modulus for 6061 aluminium
2. look up Young's Modulus for 18-8 stainless steel
~70GPa, ~200GPa
3. calculate cross-sectional area of a 2.0mm SS spoke
πmm^2
4. calculate the amount of elongation of a 290mm spoke at 1000-1300 N.
5. calculate the decrease in elongation needed to reduce tension by 5-10%
CBF figuring how to do that ATM

Also what can you conclude by comparing #1 versus #2???
Maybe that although the rim will be distorted by spoke tension easily enough, it generally isn't since the stainless increases tension rapidly compared to elongation?
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Old 12-26-09, 10:40 PM
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This simple piece of freeware (really) can convert all sorts of things, like ATM's to mm/Hg etc., for all sorts of applications. Have fun:

https://joshmadison.com/software/convert-for-windows/

Download free to your computer.
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Old 12-27-09, 04:34 AM
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Originally Posted by Kimmo
Also what can you conclude by comparing #1 versus #2???
Maybe that although the rim will be distorted by spoke tension easily enough, it generally isn't since the stainless increases tension rapidly compared to elongation?
You got half of it. Yes, due to the much, much higher stiffness of stainless steel, it generates tension with minimal elongation. Aluminium however, is 1/3rd the stiffness and for the same tension, it will elongate 3x as much as steel given the same force.

Do a test with a bare spoke and bare rim. Pull on opposite ends of the spoke with as much force as you can and notice how it feels and see how much it stretches. Then push on the bare rim and see how much it compresses into an oval. Notice any differences?

Basically in a coupled system where the same force goes from one part to the other, the weaker one will "give" more from the same force. The rim doesn't have to compress much in order to reduce spoke-elongation enough to reduce tension by 5%. Check out Jobst Brandt's book.

Heck, we don't even have to debate arm-chair physics and bike-mechanics of the various "whys" and "how" something works. Just get a tensionmeter and check it out yourself.
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Old 12-27-09, 11:48 AM
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Ooh, you guys are so sexy when you talk technical!
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