Spoke Tensionometer

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jb
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Re: Spoke Tensionometer

Post by jb »

In a thought experiment it would be possible to screw half the nipples on one half of the wheels fully down then tension the other half so all spokes were the same tension. This would produce an evenly tensioned wheel that was eccentric. Thus showing that even tension does not equate to a theoretically perfect wheel.
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Mick F
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Re: Spoke Tensionometer

Post by Mick F »

rogerzilla wrote: 30 Oct 2022, 5:26pm I can get the Park one into a x2 406 wheel. May be a smaller-diameter hub, though.
Yes, my rear wheel has a 36h SA 3sp, and no doubt the bike as originally fitted with a Miche small-flange 28h there would be plenty room.
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MikeF
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Re: Spoke Tensionometer

Post by MikeF »

jb wrote: 30 Oct 2022, 6:02pm In a thought experiment it would be possible to screw half the nipples on one half of the wheels fully down then tension the other half so all spokes were the same tension. This would produce an evenly tensioned wheel that was eccentric. Thus showing that even tension does not equate to a theoretically perfect wheel.
By "eccentric" do you mean "dished"?
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jb
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Re: Spoke Tensionometer

Post by jb »

MikeF wrote: 31 Oct 2022, 1:44pm
jb wrote: 30 Oct 2022, 6:02pm In a thought experiment it would be possible to screw half the nipples on one half of the wheels fully down then tension the other half so all spokes were the same tension. This would produce an evenly tensioned wheel that was eccentric. Thus showing that even tension does not equate to a theoretically perfect wheel.
By "eccentric" do you mean "dished"?
No, I mean off centre like a circus bike.
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MikeF
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Re: Spoke Tensionometer

Post by MikeF »

Hm. I'm not sure about your thought process. A rim is off centre of a symmetrical hub if the spokes are not the same tension on each side.
"It takes a genius to spot the obvious" - my old physics master.
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Re: Spoke Tensionometer

Post by jb »

MikeF wrote: 31 Oct 2022, 2:14pm Hm. I'm not sure about your thought process. A rim is off centre of a symmetrical hub if the spokes are not the same tension on each side.
I'm not talking about the dish, I mean that even though its possible to have all the spokes at exactly the same tension it does not automatically follow that the wheel will be true (assuming a perfect rim)
Like wise, a non dished wheel could have a lateral swash or side to side movement and still have equally tensioned spokes. For a wheel to be true it needs equal tensioning 'and' spokes of exactly equal lengths (& a perfect rim), which is the tricky bit for a hand built wheel as even when starting off with all the nipples screwed to the point were the thread disappears errors will creep in which have to be corrected.

Dishing simply adds an unnecessary complication for the purpose of the thought experiment.
Last edited by jb on 31 Oct 2022, 2:42pm, edited 1 time in total.
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Airsporter1st
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Re: Spoke Tensionometer

Post by Airsporter1st »

MikeF wrote: 31 Oct 2022, 2:14pm Hm. I'm not sure about your thought process. A rim is off centre of a symmetrical hub if the spokes are not the same tension on each side.
I thought the same - but then realised jb was talking about radial eccentricity, where both left and right spokes would be shorter over half of the circumference, such that the hub would no longer be centred radially in the rim.
rogerzilla
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Re: Spoke Tensionometer

Post by rogerzilla »

You have to build some Brompton wheels like that, as the standard el cheapo front hub is often drilled off-centre.

The wheel ends up concentric to the axle but not to the hub shell. It looks wobbly but runs ok.
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Re: Spoke Tensionometer

Post by MikeF »

Airsporter1st wrote: 31 Oct 2022, 2:41pm
MikeF wrote: 31 Oct 2022, 2:14pm Hm. I'm not sure about your thought process. A rim is off centre of a symmetrical hub if the spokes are not the same tension on each side.
I thought the same - but then realised jb was talking about radial eccentricity, where both left and right spokes would be shorter over half of the circumference, such that the hub would no longer be centred radially in the rim.
Thanks. Hard to see what was meant. I think most people building a rim would ensure it is radially and laterally true. I do, but I'm not a professional wheel builder; my wheels seem to be fine for my use.

Assuming a perfect rim, then each spoke should have the same tension (on each side) and emit the same note. That requires a tension and frequency meter. I don't have a tension meter and just rely on a radial true rim (as near as I can make it) and equal sound of the
spokes from each side as far as possible.
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Mick F
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Re: Spoke Tensionometer

Post by Mick F »

i took a punt on a £16 tool more of a test rather than a necessity.
The front wheel - radial both sides - the tool worked admirably.

The rear, only 50% as it wouldn't go in on the drive side, but it was still useful for the radial left side.

I enjoyed the trial, and I've - and am still - enjoying this thread.
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531colin
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Re: Spoke Tensionometer

Post by 531colin »

jb wrote: 31 Oct 2022, 2:40pm ...........Like wise, a non dished wheel could have a lateral swash or side to side movement and still have equally tensioned spokes. For a wheel to be true it needs equal tensioning 'and' spokes of exactly equal lengths (& a perfect rim), which is the tricky bit for a hand built wheel as even when starting off with all the nipples screwed to the point were the thread disappears errors will creep in which have to be corrected.
............
But spoke length and tension are not independent variables.
The effective length of the spoke is the length from the elbow bend where it fits the hub to the underside of the nipple where it fits the rim.
As you say, you can have an area of lateral run-out with identical tensions both sides; slacken one side a quarter turn, tighten the other side a quarter turn and you may achieve a true wheel with identical tensions.....all you have done is alter the effective spoke length by a quarter of the thread pitch.

If you are going to buy a tension gauge, the sensible time to use it is as soon as you start getting some tension on the spokes, and throughout the rest of the build. If you "finish" the wheel and then use the gauge to "check" the tensions, you either have to ignore the tension readings you have just got, or set about balancing the tensions.

My "final repeating cycle" is......stress the wheel, true the wheel, balance the tensions......repeat, repeat,.....until I get a stable wheel with a proper balance between trueness and evenness of tension. (a stable wheel is a wheel which doesn't go out of true when I lean on the rim with the axle end supported...this is not stress-relieving the spokes, which is done once as soon as the spokes are at full tension, and the wheel reasonably true)
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Re: Spoke Tensionometer

Post by jb »

531colin wrote: 2 Nov 2022, 7:04am
jb wrote: 31 Oct 2022, 2:40pm ...........Like wise, a non dished wheel could have a lateral swash or side to side movement and still have equally tensioned spokes. For a wheel to be true it needs equal tensioning 'and' spokes of exactly equal lengths (& a perfect rim), which is the tricky bit for a hand built wheel as even when starting off with all the nipples screwed to the point were the thread disappears errors will creep in which have to be corrected.
............
But spoke length and tension are not independent variables.
The effective length of the spoke is the length from the elbow bend where it fits the hub to the underside of the nipple where it fits the rim.
As you say, you can have an area of lateral run-out with identical tensions both sides; slacken one side a quarter turn, tighten the other side a quarter turn and you may achieve a true wheel with identical tensions.....all you have done is alter the effective spoke length by a quarter of the thread pitch.

If you are going to buy a tension gauge, the sensible time to use it is as soon as you start getting some tension on the spokes, and throughout the rest of the build. If you "finish" the wheel and then use the gauge to "check" the tensions, you either have to ignore the tension readings you have just got, or set about balancing the tensions.

My "final repeating cycle" is......stress the wheel, true the wheel, balance the tensions......repeat, repeat,.....until I get a stable wheel with a proper balance between trueness and evenness of tension. (a stable wheel is a wheel which doesn't go out of true when I lean on the rim with the axle end supported...this is not stress-relieving the spokes, which is done once as soon as the spokes are at full tension, and the wheel reasonably true)
I absolutely agree. (not that I'm in the habit of disagreeing with professional builders :) )
I think Micks 'experiment' was if you concentrated on equal & exact spoke tension then a true wheel would automatically be the result but that would only be true if the nipples were all precisely set at the same length to start with and then adjusted by exactly the same amount on each and of course the rim was perfectly drilled (and assuming most decent hubs are accurate these days), and that's ignoring the de stressing process.
This process might work on the 'London Eye' but is probably impractical in a back shed workshop.
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MikeF
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Re: Spoke Tensionometer

Post by MikeF »

Longer spokes at the same tension as shorter ones would vibrate at a lower frequency.
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NATURAL ANKLING
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Re: Spoke Tensionometer

Post by NATURAL ANKLING »

Hi,
pete75 wrote: 30 Oct 2022, 3:18pm
NATURAL ANKLING wrote: 29 Oct 2022, 9:44pm Hi,
Its possible to get even tension in spokes but the wheel could be wavy.
Thats to say that the rim could be parralel to aflat plane, but be out of true and still have even tension spokes.

It won't (tool) build a wheel, you need to do that and true wheel yourself.

Its a comparitor.
I've always thought you need to get spoke tensions as even as possible consistent with the wheel being true.
It's possible to build a "true" wheel with widely differing tensions. It won't last long though.
Like wise you could have even tension spokes but a run out.
As you said - even spoke tension and true is ideal.
Brucey quoted that even tension is more important than getting the rim perfect.
Of course a rim braked wheel does need realative trueness to be useable, a disc not so.
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NATURAL ANKLING
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Re: Spoke Tensionometer

Post by NATURAL ANKLING »

MikeF wrote: 3 Nov 2022, 8:20am Longer spokes at the same tension as shorter ones would vibrate at a lower frequency.
So you are looking for same note (frequency) only on the same side rear dished wheel.
Front non disc is all the same note. assuming all other things equal.
Unibalance (which shimano pioneered, and I used on my devon and cornwal coast ride with 32 spokes, with lugage) uses a very low dish ratio (spokes are Off the top of my head barely 1 MM diffence side to side, well you use 2 MM diff but their effective assemble length is 1 MM) :)
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