Spoke Tension Meter, Hows This Work?

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Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 2 Jan 2019, 7:45pm

I agree that does stop the nipples from backing out, and it is good standard practice to do this.

However if the spokes go slack enough they can also be flexed in an unusual way and that can break them prematurely, with or without threadlock. It is also that case that the whole wheel is liable to be flexing 'quite a lot' when all this is happening too. It is -if it is possible at all- without doubt a better idea to build wheels that are better specified for the task in hand and don't suffer from such large in-service variations in spoke tension.

Thus when building wheels with unknown parts for known riders and/or known parts for unknown riders, I will quite often build the rear wheel without threadlock on the NDS spokes initially. After a couple of weeks of use I look at them again and any big problems ought to be evident; the NDS nipples will have started to back out. At this stage you can make a rational choice between simply adding threadlock and retensioning the wheel, or indeed specifying different parts for that particular use. You can learn quite a lot by looking at how the spokes have been moving around in the hub; lots of movement means the largest possible excursions in tension and in this case it is likely that the wheel will not be reliable even with threadlock applied.

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gxaustin
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Re: Spoke Tension Meter, Hows This Work?

Postby gxaustin » 3 Jan 2019, 11:52am

What sort of percentage of variation between spokes one side is acceptable?
Or is the meter readings too crude / influence by operator / poor repeatable reading, etc.
So you can fiddle it to read the same / satisfy yourself they are the same in different spokes.
Depends on the meter I suppose.


My wheels have tension variations within or about 5% (according to the meter) with radial out of true up to 1mm and horizontal less than 0.5mm. I find this is OK for practical riding. The difference between drive side and nds is about 10% on my wheels.

I did have one accident with a "U" shaped rim. I decided to put a freehub in a 27" wheel and had trouble getting it round. This was before I had a meter to check. As I stress relieved the wheel it assumed the shape of a Pringle :lol: . Of course a simple "U" shape has little or no torsional rigidity (remember the Milford Haven Bridge collapse - that was a torsional failure of a U shape before the web was welded on).
I built the wheel eventually and checked the spoke tensions were OK but have never used it. Maybe one day :?:

Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 3 Jan 2019, 12:38pm

FWIW typical tension balances with various hubs (and conventionally spoked/dished wheels) are

130mm OLN 11s...………………………….....…..~45%
130mm OLN 8/9/10...…………………………….~49%
130mm OLN 11s with 2.5mm offset rim...…..~56%
130mm OLN 8/9/10s with 2.5mm offset rim ~60%
135mm OLN 8/9/10 ……………………………………... ~62%
135mm OLN 8/9/10 with 2.5mm rim offset …. ~75%
135mm 7s ………………………………....................~77%
Shimano Alfine 8s IGH....................................80%
135mm 7s with 2.5mm offset rim.................~93%
Shimano Alfine 8s IGH with 2.5mm offset rim......…~95%

you can see that getting a 10% reduction in the NDS spoke tension ( a 90% balance) simply isn't possible with a wide range of conventional derailleur wheel builds. It requires modification to the hub, a different dish (i.e. an offset wheel and/or rim) or something.

FWIW my touring bike uses a 7s 135mm hub, but respaced and with a modified freehub body so that the tension balance is between 90 and 95% even without an offset rim.

cheers
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gxaustin
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Re: Spoke Tension Meter, Hows This Work?

Postby gxaustin » 3 Jan 2019, 11:53pm

you can see that getting a 10% reduction in the NDS spoke tension ( a 90% balance) simply isn't possible with a wide range of conventional derailleur wheel builds. It requires modification to the hub, a different dish (i.e. an offset wheel and/or rim) or something.


Looks like I need to check that out. I was working from my unreliable memory.

Before I do, can you explain your figures? I assume they refer to the percentage of DS tension on the NDS?

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NATURAL ANKLING
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Re: Spoke Tension Meter, Hows This Work?

Postby NATURAL ANKLING » 4 Jan 2019, 12:47am

Hi,
Originally I was asking what error or variation would be ok on Same Side spokes.
If by ear what would you expect 5-10 % difference.
DS vs NDS obvious that would be great as shown by Brucey.

My greatest problem came with re rimming a 135 mm std 8 speed using over 2mm plain spokes 11 swg.
Originally all the spokes were threadlocked from the factory (Raleigh) NDS worked loose very quickly :(
Gave up and used butted on rear, front is no problem of course.

Steel spoked wheels that are aged without much use (cheap wheels) though 135 seven speed 26" single wall, don't normally have lube on the threads? so I assume once corrosion has set in plus friction is higher I expect than stainless, never seem problematic until I thrash them on my trainer and then I will get broken spokes and normally a few winters the spokes are rusting, time to add another skip wheel which I do relieve of course.
Most of them wheels are coming from 80's & 90's, and will refurbish with any spoke the correct length thats taken from stripped skip wheels.

I had a wheel once that when broken down even though brand new and perfectly true, the rim went like a banana (sure I posted but will find it) IIRC I collapsed the rim with by bare hands such was the lightweight construction of rim. Also I think that the spokes were like coat hanger wire shape bent in the middle, you know the design.
The rim was so light that trueing the thing wouldn't of been a problem but you could never use for anything other than fetching the paper :)
Learnt more in the last two years on here with help from brucey and the like than in forty four years of rebuilding my own stuff.
Struggling a bit to keep up with some of bruceys more advanced relieving techniques of late :P
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Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 4 Jan 2019, 1:21am

gxaustin wrote:
you can see that getting a 10% reduction in the NDS spoke tension ( a 90% balance) simply isn't possible with a wide range of conventional derailleur wheel builds. It requires modification to the hub, a different dish (i.e. an offset wheel and/or rim) or something.


Looks like I need to check that out. I was working from my unreliable memory.

Before I do, can you explain your figures? I assume they refer to the percentage of DS tension on the NDS?



yes so a 10% lower tension on the NDS is the same thing as a 90% tension balance. The numbers come from simple geometry; the lateral components of the spoke tension have to equal one another side to side (else the rim wouldn't stay put). With a less angled (NDS) spoke the tension has to be lower to make the lateral component the same as that of a more steeply angled (DS) spoke.

These values obviously vary with hub design and also with spoking pattern. Those I have quoted are for 36x3 builds. You can save yourself all the bothersome arithmetic if you like; some spoke length calculators will work out the tension balance for you.

FWIW reliably identifying a ~10% variation in tension using a typical tension meter is difficult if not impossible to do; they are simply not that accurate. Hence IMHO they have some value if you have absolutely no idea about tension values but other methods (eg plucking) will work at least as well if not better if you wish to verify uniformity of tension.

Tension variations of ~10% in one side of a wheel are not uncommon and rarely cause any trouble.

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NATURAL ANKLING
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Re: Spoke Tension Meter, Hows This Work?

Postby NATURAL ANKLING » 4 Jan 2019, 11:45am

Hi
Stupid question or maybe not.
A 32 vs 36 wheel, same rim same hub, same spokes (diff length), which would need the higher tension in spoke, 3X pattern both :?:
Edited- lets say its a front equal non disc wheel.
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Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 4 Jan 2019, 12:46pm

maximum spoke tension is in most (but not all) cases limited by the rim. Typical limits are set by

- the rim self-pringling ( mostly single wall rims)
- the rim cracking in service
- the spokes pulling through directly.


The minimum acceptable spoke tension will vary with the service loads applied and for otherwise identical conditions will be slightly higher for a 32 spoke wheel than a 36 spoke wheel.

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gxaustin
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Re: Spoke Tension Meter, Hows This Work?

Postby gxaustin » 4 Jan 2019, 4:48pm

FWIW reliably identifying a ~10% variation in tension using a typical tension meter is difficult if not impossible to do; they are simply not that accurate. Hence IMHO they have some value if you have absolutely no idea about tension values but other methods (eg plucking) will work at least as well if not better if you wish to verify uniformity of tension.



I have found my mistake - the readings on the tension meter are related to actual tension by a very very non linear relationship. The actual ratio is about 3:1 on a 135mm Deore hub, which has proved very reliable. Because I only use the meter to check uniformity I never look at the tension tables - oops.


Thanks for the extra information too.

MikeDee
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Spoke Tension Meter, Hows This Work?

Postby MikeDee » 5 Jan 2019, 12:32am

How about measuring the actual strain (elongation) of the spoke? Without doing any calculations, I've heard that spokes stretch about 1mm (~.039") when at final tension; easily measurable with a vernier caliper. Stress = E * strain. Will measuring over an inch provide enough accuracy? What do you think Brucey?

NickJP
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Re: Spoke Tension Meter, Hows This Work?

Postby NickJP » 5 Jan 2019, 5:44am

MikeDee wrote:IMO, you should use some form of threadlocker on the NDS spokes to keep the spoke nipples from loosening. Spoke tension alone is inadequate for a wheel with 130mm OLN hubs to keep NDS spoke nipples from loosening.

I haven't found NDS spoke loosening to be a problem on wheels I've built, including quite a number of 11s 130 OLN wheels over the past few years, and I don't use threadlocker. Indeed, the first thing I do with nipples is to open the packet, drop them into a sieve, submerge them in oil, let them drain, and store them in a bottle until use.

When building a wheel, you need to set the spoke tension about 10-15kgf higher than the final value you want, as installing and inflating the tyre will cause the tension to drop by about this amount.

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Brucey
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Re: Spoke Tension Meter, Hows This Work?

Postby Brucey » 5 Jan 2019, 8:18am

most strong riders will quite easily cause NDS nipples to back out in 11s 130mm OLN wheels if they are lubricated rather than threadlocked. They have (pretty unavoidably) about half the tension of the DS spokes.

The extent to which the rim moves and the spoke tension is lost when the tyre is inflated varies quite a lot with the type of rim; with some rims the effect is negligible and with others it is fairly profound. The amount of tension lost varies with the spoke type as well, of course; stiffer spokes lose more tension than skinnier, stretchier ones.

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531colin
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Re: Spoke Tension Meter, Hows This Work?

Postby 531colin » 5 Jan 2019, 9:01am

gxaustin wrote:……. The actual ratio is about 3:1 on a 135mm Deore hub,............


What "ratio"?
135mm OLN 8,9,10 speed come out at 80 vs 120 Kgf NDS vs Driveside.

gxaustin
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Re: Spoke Tension Meter, Hows This Work?

Postby gxaustin » 5 Jan 2019, 2:43pm

What "ratio"?


Ratio: the quantitative relation between two amounts showing the number of times one value contains or is contained within the other. :wink:

I don't think that calibration is very good because the wheel is true and the rim is central and there are equal numbers of spokes either side - but there again I use it for uniformity not actual values.

Samuel D
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Re: Spoke Tension Meter, Hows This Work?

Postby Samuel D » 5 Jan 2019, 3:22pm

If it’s so far out that it shows the right:left tension ratio on a Deore hub to be 3:1, I would have low confidence that it’s useful for measuring tiny differences in tension.

Does being tone-deaf (not that you’ve said you are) mean one cannot sing a note or one cannot tell which of two notes in quick succession is higher? I am no singer, but my ear can tell which of two spokes has higher tension with greater precision than even my Wheel Fanatyk tensiometer – which is itself better (more repeatable) than the Park Tool tensiometer and its copies.

I find a tensiometer useful for getting the final tension as high as the rim specifications permit, especially for the right spokes of a rear wheel. It is surprisingly hard to judge this by squeezing spokes, just as it’s hard to guess tyre pressure by poking your thumb into the sidewall. On different days, with different spoke gauges and span lengths, having warmed up your hands (or thumb) with heavier or lighter work beforehand, and squeezing from different postures and angles with varying levels of mental and physical energy and caffeine, you get different results. Having a known good wheel to compare against is a better approach, but even that has its limits for lightweight wheels that must be built close to their structural limits to achieve acceptable reliability.

I like 36-spoke wheels with conservative components that make all of this less critical. The performance benefit of lighter wheels is vanishingly small anyway.