# NDS spoke tension?



## Matador-IV (Aug 2, 2010)

Once I achieve proper DS tension and dish, do I just let the NDS tension 'fall where it may'?

If not, is there a minimum tension I should try to achieve, which ultimately would require me to increase the DS tension to maintain the dish.

thanks.


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## ergott (Feb 26, 2006)

It should be even. The absolute number is irrelevant.

Good luck and post your results.

-Eric


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## TomH (Oct 6, 2008)

The absolute number is important. If your hub geometry dictates that at a given DS tension, your NDS tension is something like 30 kgf.. you picked the wrong hub, rim, or DS tension. 

Theres nothing you can do about the ratio, but its a consideration before buying stuff. You really want the NDS tension as high as it'll go, given the rest of the constraints. If your nds number is terribly low, it might be worth considering 1x heads in lacing on the DS. 

If you're planning a heads out DS wheel with a big wide nds flange and 16mm ds spacing and want a max ds tension of 90.. your nds tension is going to suck, and you should reconsider. 

If you've got a normal hub, normal rim, and normal 2 or 3x lacing, then NDS tension is what is is, and you shouldnt worry about it.

A few months ago a guy ran into this exact situation.. he had a hub and lacing combo that resulted in his NDS spokes going slack while riding and busting constantly. His DS tension was maxed out. He had a flexy rim and radial NDS spokes on a hub that wasnt compatible.


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## ergott (Feb 26, 2006)

If you are at the point where you already laced and tensioned the wheel it's too late to consider your points;-)

-Eric


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## Matador-IV (Aug 2, 2010)

HA!! Guess I should have given some specifics.

50mm carbon rims
Dati hubs 
Sapim Cx rays
2x lacing both sides

Most importantly, this is my first wheel build so learning as I go.


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## ergott (Feb 26, 2006)

What are the Dati hub dimensions?

You can get the ratio by the ratio of the flange spacing.

18mm right flange and 36mm left flange will have 50% tension on the left side.

-Eric


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## twinkles (Apr 23, 2007)

TomH said:


> it.
> 
> A few months ago a guy ran into this exact situation.. he had a hub and lacing combo thatresulted in his NDS spokes going slack while riding and busting constantly. His DS tension was maxed out. He had a flexy rim and radial NDS spokes on a hub that wasnt compatible.


 I ahd a friend with that same problem. I replaced the non drive spokes, which were 14-15, with revolution spokes and that's takn care of the problem.


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## SBH1973 (Nov 21, 2002)

DATI hubs:


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## Matador-IV (Aug 2, 2010)

Flange spacings are 19mm and 32mm

So am I correct in sayin that the NDS, ideally, would be at least 60% of the drive side.


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## TomH (Oct 6, 2008)

A hair under, but yeah. Not bad flange spacing!


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## teleguy57 (Apr 23, 2006)

At what point do you consider a lighter NDS spoke to get to a more even tension? Is it a particular %, or does flange diameter come into play, or....? Or a different way to ask, at what point doesn't it matter much if you use the same DS/NDS spokes (assume 14/15 db for DS)...


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## TomH (Oct 6, 2008)

You can always use the same spokes when doing similar crosses.. 1x both sides, 2x both sides, 3x both sides etc etc. 

Its more rare that you cant and really only a problem when you're doing things you shouldnt be doing anyway, like radial lacing the NDS on an inappropriate hub. 

Beyond that.. Im not sure if it would ever be a bad idea to use a lighter NDS unless you have some sort of arrangement where the NDS is 100% of the DS. Kinda just adds cost.


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## Drew Eckhardt (Nov 11, 2009)

teleguy57 said:


> At what point do you consider a lighter NDS spoke to get to a more even tension?


Spoke diameter has no effect on tension.

Drive side spoke stiffness with respect to tensile/compressive loads (which comes from thickness) + hub torsional stiffness + NDS stiffness are what determines how far the hub winds up.

With thinner NDS spokes than DS windup will be somewhere between what it would have been with thick spokes on both sides and thin spokes on both sides. Since thinner spokes change length more for a given tensile/compressive load or conversely have as smaller change in tension for a given length delta the trailing spokes retain more tension and are less likely to have nipple rotation. 



> Is it a particular %, or does flange diameter come into play, or....? Or a different way to ask, at what point doesn't it matter much if you use the same DS/NDS spokes (assume 14/15 db for DS)...


I've built Campagnolo wheels (with a greater tension imbalance than Shimano due to the wider freehb) with straight 14 gauge spokes on both sides and DT 2.0/1.5 Revolutions non-drive side + DT 2.0/1.8 Competitions drive side. They all work fine.

I rode a Campagnolo Powertap wheel with DT 2.0/1.8 spokes all around laced cross-3. It worked fine too.

I rode some one else's wheels with DT 2.0/1.8 spokes all around. Rear NDS spokes were constantly going loose and the front wheel collapsed. I blamed the builder for both and stopped delegating my wheel construction.

I'd guess that perhaps apart from exceptional situations (Maybe high spoke count Stan's Alphas where tension is limited due to the light extrusion, tubeless tires which cause a significant tension drop, and sub-optimal flange spacing) lighter NDS spokes give the builder more latitude to screw up before some one notices (just like boiled linseed oil or tacky spoke prep) but aren't required.


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## rruff (Feb 28, 2006)

Drew Eckhardt said:


> Drive side spoke stiffness with respect to tensile/compressive loads (which comes from thickness) + hub torsional stiffness + NDS stiffness are what determines how far the hub winds up.


Windup isn't usually the issue. The NDS spokes go slack from radial and lateral loads. If you make them thinner, then more of the load is carried by the stiffer DS spokes, and the NDS spokes will be less likely to go slack. 

I rarely build this way though and instead use CX-Rays ( which are as light as you can get) on both sides. If the hub has decent geometry and the build is appropriate for the rider, there won't be any problems.

EDIT: In this particular case there the NDS tension will be plenty high. I'd recommend radial heads-in on the NDS to increase the bracing angle if the spokes haven't been purchased yet.


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## eddie m (Jul 6, 2002)

Drew Eckhardt said:


> ... lighter NDS spokes give the builder more latitude to screw up before some one notices... but aren't required.


I like using lighter NDS spokes. It's a lot easier to bring a straight gauge spoke to high tensions (I'm not a pro builder and I don't have mad wrenching skills), and you have a larger margin for tension error. With an extremely offset hub (like a Campy), you need to bring the drive side close to it's maximum tension to have adequate NDS tension. Using different gauge spokes is a cheap way to increase the margin of error.
I gave up on local wheelbuilders around here because they insisted they could tension a wheel by "feel." That may have been true when they were building 36 spoke 5 speed wheels (although those wheels were way less reliable than modern factory wheels), but with 10 speed wheels he margin for error is practically zero. 
I always measure tension on all the wheels I build so that I know I have a reliable wheel. I did some research in a job I had a few years ago, and IIRC the results were that experienced mechanics could tighten a bolt with +/-30% accuracy using a torque wench, and about +/-80% accuracy going by feel. That's not exactly the same thing as building a wheel, but it demonstrates the importance of measurement. 

em


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## teleguy57 (Apr 23, 2006)

Ron, can you get the same results using Lasers instead of CX-Rays to save a bit on the cost of the spokes?


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## Andreas_Illesch (Jul 9, 2002)

Drew Eckhardt said:


> Spoke diameter has no effect on tension.


 What?



Drew Eckhardt said:


> Drive side spoke stiffness with respect to tensile/compressive loads (which comes from thickness)


 thickness, that has something to do with diameter, right?



Drew Eckhardt said:


> With thinner NDS spokes than DS windup will be somewhere between what it would have been with thick spokes on both sides and thin spokes on both sides. Since thinner spokes change length more for a given tensile/compressive load or conversely have as smaller change in tension for a given length delta the trailing spokes retain more tension and are less likely to have nipple rotation.


The tensile load (there is no compressive one with spokes) on the NDS is always lower than on the DS due to dish so the elongation of the spokes on both sides may be quite similar if there are thick spokes on the DS and thin spokes on the NDS.


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## TomH (Oct 6, 2008)

d2/d1, d2 being the DS offset, d1 being the NDS offset is proportional to t2/t1, t being tension. 

Spoke diameter has nothing to do with tensions value. The above proves that. Elongation does is related to spoke size. 

elongation = (force)(length original) / (cross section area * modulus of elasticity)

without getting too far into it.. the cross section area is the diameter of the spoke (squared times pi over 4). For the same force, a larger diameter gives a bigger denominator, thus smaller elongation.


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## Andreas_Illesch (Jul 9, 2002)

The tension in the single spoke depends on it's diameter (and on the force that pulls the spoke).
Thicker spoke -> less tension, thinner spoke -> more tension (given the same force).



"d2/d1, d2 being the DS offset, d1 being the NDS offset is proportional to t2/t1, t being tension. "

The distribution of loads between DS and NDS depends on the sine of the lateral angles.
That includes the offsets and different flange diameters (as there are with some hubs).


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## eddie m (Jul 6, 2002)

TomH has it right, but flexible structures are difficult to analyze and explain. 
if you replace a spoke with a lighter one, the lighter spoke needs to be brought up to the same total tension as the spoke it replaces. In order to have that tension, it needs to stretch more. the stress in the lighter spoke is higher, even though the total tension is the same. When you load up the wheel, the stronger spokes take more of the load, the lighter spoke takes less of it. Because the lighter spoke takes less of the load, it is less likely to go slack than the spoke it replaced. You get a more reliable wheel than one in which spokes frequently go slack, but t weaker one because most of the load is supported by fewer spokes. Most wheels are more than strong enough, so the trade off of strength for reliability is usually worthwhile.

Hope this helps.

em, P.E.


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## eddie m (Jul 6, 2002)

Double post.


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## TomH (Oct 6, 2008)

Proportional triangles.. you're saying the same thing Im saying, but using a formula thats a bit harder to calculate. (oops, t1/t2!) 

Using that formula, and the 19/32 spacing.. we get:

19/32 = t1/120.. which works out to 72, or 60%. 

The NDS tension will be 60% of the DS tension. 

100kgf is 100kgf, no matter what its applied through, by the nature of a force like that. You could use a heavy rubber band, if it could hit 72 kgf it would be stretched to hell, but it would balance the tension (and also never go slack!).

edit: eddie beat me to it. PE = professional engineer?


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## Andreas_Illesch (Jul 9, 2002)

eddie m said:


> if you replace a spoke with a lighter one, the lighter spoke needs to be brought up to the same total tension as the spoke it replaces.


No, it has to bear the same FORCE/load as the thicker spoke, if you want that wheel as round as it was with the thicker spoke.
Therefore the thinner spoke will have a higher tension than the thicker spoke before.
Same force, thinner spoke -> more tension in the spoke, as I wrote above.


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## eddie m (Jul 6, 2002)

Andreas_Illesch said:


> The tension in the single spoke depends on it's diameter (and on the force that pulls the spoke).
> Thicker spoke -> less tension, thinner spoke -> more tension (given the same force).


You are confusing stress with tension here. The tension in the spoke depends only on what the wheel needs to be true. The stress in the spoke is that tension divided by the crossection area, so a thinner spoke has more stress.


Andreas_Illesch said:


> The distribution of loads between DS and NDS depends on the sine of the lateral angles.
> That includes the offsets and different flange diameters (as there are with some hubs).


The pre-load tension in the spokes is proportional to the sines, and the sines are proportional to the offset of the flanges from the centerline, so you can as easily estimate the requires preloads from the offsets as from the sines. The change in tension of the spokes as the loaded wheel rolls is a function of a number of factors, including the elasticity of the spokes and rim, and the position of the spokes. All else equal, in a wheel with spokes of different gauges, the heavier gauge spokes will experience a greater tension change than the lighter ones.

em, P.E.


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## Andreas_Illesch (Jul 9, 2002)

TomH said:


> Proportional triangles.. you're saying the same thing Im saying,


I added the different flange diameters.


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## eddie m (Jul 6, 2002)

Andreas_Illesch said:


> No, it has to bear the same FORCE/load as the thicker spoke, if you want that wheel as round as it was with the thicker spoke.


That's right. FORCE = Tension. Your analysis is right, but you are using incorrect definitions.

em, P.E.


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## TomH (Oct 6, 2008)

Well.. lets get some basics established. 

A wheel has two spokes installed. They are opposite to eachother, on the same flange, on a rim. The rim has infinite strength and no flex for the sake of keeping it simple.

so its -------0-------- . Just two spokes opposing eachother. 

The spoke on the left is a monster 4mm spoke. The spoke on the right is a tiny 1mm spoke. 

The 4mm spoke is tensioned to 100 kfg. Its 4 times as thick as the tiny right spoke. Whats the tension in the 1mm spoke?


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## Andreas_Illesch (Jul 9, 2002)

eddie m said:


> The stress in the spoke is that tension divided by the crossection area, so a thinner spoke has more stress.


Oh, sorry I mixed that up, English is not my native tongue.



eddie m said:


> and the sines are proportional to the offset of the flanges form the centerline,


I still miss different flange diameters here.


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## eddie m (Jul 6, 2002)

Andreas_Illesch said:


> I still miss different flange diameters here.


You are also right that sine are more accurate if the flange diameters are different, but it's simpler to use the hub offset and usually accurate enough as well.

TomH
That's a variation on the simplest statically indeterminate structure problem. Are you an engineer?
em


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## TomH (Oct 6, 2008)

Working towards it, but hows it indeterminate (I really dont know. I thought assuming fixed supports that dont flex at all would make it statically determinant)? Was just trying to show force vs stress. They'd both have 100kgf tension. 

I think it was a term mixup and cleared up now though  The 3 of us were kinda posting at the same time.


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## eddie m (Jul 6, 2002)

TomH said:


> Working towards it, but hows it indeterminate (I really dont know. I thought assuming fixed supports that dont flex at all would make it statically determinant)? Was just trying to show force vs stress. They'd both have 100kgf tension.


It's indeterminate because you can't determine the internal stress cause by an external load without knowing the elasticities of each element.

em


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