Wheels - how much dish before plain gauge spokes are advisable?

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slowster
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Wheels - how much dish before plain gauge spokes are advisable?

Post by slowster »

It is often recommended that plain gauge spokes should be used on the drive side of a rear derailleur wheel, and butted on the non-drive side. Chris Juden's explanation for this is here - viewtopic.php?p=130576#p130576.

100mm OLN front disc wheels are also dished, but I have not seen anyone suggesting that plain gauge spokes should similarly be used for the disc side. I suspect that might be because front wheels are far less stressed, and so the potential benefit of using plain gauge spokes would be much less. Neverthless the introduction of the 110mm OLN standard for MTB front wheels in order to eliminate/reduce the dish appears to suggest that the dish is a concern, albeit possibly only for severe MTB use.

I wonder therefore at what point the amount of dish makes it advisable to use plain gauge spokes on the dished side. Even for rear derailleur wheels there will be those cases where it presumably will be best to use butted spokes on both sides because the dishing is not great enough to make plain gauge a better choice (such as possibly a low dish 7 speed 135m OLN hub).

Presumably the tipping point would be determined by/measured by the spoke tension differential. For example, I would guess that a 90% spoke tension on the non-dish side is too low a differential for plain gauge spokes, whereas the 50%-60% differentials of modern 10/11 speed 130mm OLN hubs will almost certainly benefit from plain gauge spokes on the drive side. But what about in between those extremes?
Last edited by slowster on 27 Jan 2022, 2:07pm, edited 1 time in total.
alexnharvey
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by alexnharvey »

Another option now is to use thicker and thinner butted spokes, for example there are spokes available with butted sections of 1.5, 1.65 and 1.8mm, so rather than plain gauge you might use the 1.8s on the drive side and 1.5s or 1.65s on the non-drive side if the dishing is less severe.

Following CJ's post I used some DT alpine III spokes on some wheels but the heavy gauge 13g/2.3mm elbow is quite difficult to 'set' compared to 2mm spokes.
esasjl
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by esasjl »

Make spoke cross-sectional area ratio the same as the tension ratio to maintain parity of spoke extension (stress). 1.5 with 1.65 mm for 80/85%, 1.5 with 1.8 for 70% and 1.5 with 2.0 for 55%.
MartinC
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by MartinC »

I think one can over think this. AIUI the purpose of butted spokes on the less tensioned NDS is so that they stretch more and don't lose tension when they're unloaded allowing the elbow to fatigue. On the DS side they have to be able to cope with more tension but they don't have to cope with the loss of tension scenario. I'm not sure there's any benefit beyond this
Jamesh
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by Jamesh »

I don't think plain gauge add anything but weight.

The majority of stress in a spoke is at the elbow so being plain gauge or butted makes no odds. In fact thinking about it the inflexible plain gauge spoke will transfer more flexing to the elbow where as a butted spoke will flex more.

I've only built a couple if wheelsets though.....
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531colin
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by 531colin »

To be fair, I'm too old, and its too late in the day for me to think about anything complicated.
However, this is the time and facilities that I have, so.......

Brandt experimented with tension vs elongation, and got remarkably little difference between plain and butted spokes.
for DT butted spokes he got 1mm elongation at about 120Kg.
For plain, it was about 135Kg for 1mm elongation.
Not a huge difference? (probably not exactly what we need to compare, but its the numbers I've got)
Somebody better at maths than me ( a fairly low bar) should be able to calculate this from Youngs Modulus, the cross-sectional area and stuff like that? (actually, Youngs Modulus is a constant, so its just the difference in cross-section area for plain vs. butted?)

I'm sure Sapim used to publish on their website all sorts of information about their spokes....even stuff like number of fatigue cycles to failure,,,,,but i can't find anything now.

Brandt also calculated effects of a load on a theoretical wheel. He said that about 4 spokes worth of rim flattened a bit at the bottom under load.....this was the "load affected zone". He calculated the "shortening" of each spoke resulting from the "flattening" of the rim at the bottom due to a load of 50kg at the axle.
For an un-specified rim in an un-specified wheel loaded with 50kg at the axle the maximum shortening he got was 0.15mm for a radial spoke,
but 0.05mm for a tangential spoke (tangential to the hub flange)
Thats a massive difference, unless I mis-understand.... 3 times ?! Much more than the difference in elongation of plain/butted spokes for the same load

So, my conclusion, such as it is.........its very elegant and intellectually satisfying to match the spoke tension to its stiffness. But I'm not sure it matters at all.

If a 50 kg load deflects the rim so little that a (crossed) spoke shortens by 0.05mm, then (if its all linear) a 500kg load will give a 0.5mm shortening....this is less than the elongation above, ie the spoke won't go slack.
Brandt's book is published 1981, so he isn't talking about modern deep rims?

Even if non driveside spokes do go slack, if Brandt is right and the load affected zone covers just 4 spokes, then the displacement of the rim will be absolutely tiny....within the elastic deformation range of the rim, not enough for the rim to take a set.

Slackening of NDS spokes is a problem in the real world in the case of 130mm 11 speed wheels with a light rim and a powerful rider.....this is due to rider weight, pedalling torque on the hub, and other esoteric stuff like side force (yaw?) due to the weight of the rider's legs going up and down, and riding out of the saddle. The remedy which is usually recommended is to threadlock the nipples, rather than use spokes with much greater difference in thickness.

I'm not much use as a tester....i have never been much over 11 stone, and I'm now old and weak......added to that I have never, ever, broken a spoke in any wheel which I have built for myself.
So I can't attach much importance to the fact that I still haven't broken a spoke or had any other wheel problems since I stopped using spokes of different thickness on the different sides of a rear wheel. (and neither have other people I've built for, either)

Rim cracking at spoke holes is a problem with some rims (and road salt corrosion) and I think that using butted spokes "shares out" any load among more spokes than a similar wheel with plain spokes.
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by rogerzilla »

I don't use p/g spokes if d/b spokes are available in the right length. P/g spokes are inferior in almost every respect; I'll concede they ARE easier to build with, cheaper, and the wheel goes out of true by a bit less, should one break.

My preference is DT Comp on the drive side and DT Rev on the non-drive side. Or, if you like a challenge, DT Rev on both sides. They twist merrily during the build, and can be frustrating.

All spokes are strong enough; the important thing is keeping the NDS from becoming completely slack. Revs do this well, with their extra stretch. The tension ratio of a Shimano 11-speed wheel is a laughable 1:2.2, so the NDS spokes have very little tension unless you crank the DS spokes up to eyelet-yanking tension.
Jamesh
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by Jamesh »

What's the ratio on a 8-10spd Shimano hub out of interest?

1-1.5, 1-2.0??
pwa
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by pwa »

rogerzilla wrote: 29 Jan 2022, 9:37pm I don't use p/g spokes if d/b spokes are available in the right length. P/g spokes are inferior in almost every respect; I'll concede they ARE easier to build with, cheaper, and the wheel goes out of true by a bit less, should one break.

My preference is DT Comp on the drive side and DT Rev on the non-drive side. Or, if you like a challenge, DT Rev on both sides. They twist merrily during the build, and can be frustrating.

All spokes are strong enough; the important thing is keeping the NDS from becoming completely slack. Revs do this well, with their extra stretch. The tension ratio of a Shimano 11-speed wheel is a laughable 1:2.2, so the NDS spokes have very little tension unless you crank the DS spokes up to eyelet-yanking tension.
Speaking as someone with basic skills, I value a plain gauge drive side spokes being more resistant to twisting, as it means I am much more likely to true my wheels to near perfection at the first attempt.
Last edited by pwa on 31 Jan 2022, 5:06am, edited 1 time in total.
rogerzilla
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by rogerzilla »

Jamesh wrote: 29 Jan 2022, 10:20pm What's the ratio on a 8-10spd Shimano hub out of interest?

1-1.5, 1-2.0??
1:1.72 for the same wheel (I'm comparing DA 10 speed with DA 11 speed, but I doubt there is a difference for other groupsets).
Last edited by rogerzilla on 30 Jan 2022, 2:05pm, edited 1 time in total.
pq
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by pq »

When I build a wheel, if I think this is an issue I use thicker, single butted spokes on the drive side. I don't think there's ever any point using plain gauge spokes.
One link to your website is enough. G
slowster
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by slowster »

My thanks to everyone for the replies. Evidently there might be a theoretical benefit, but it is vastly outweighed in practice by the skill of the wheelbuilder.

I am going to build a wheel with a Shimano dynamo hub. The cheapest hub available happened to be a disc hub, and it was the discovery that the offset would result in ~70% lower spoke tension on the non-disc side that prompted me to ask my question, even though I had already decided that I would use butted spokes on both sides for that wheel.
531colin wrote: 29 Jan 2022, 6:40pm If a 50 kg load deflects the rim so little that a (crossed) spoke shortens by 0.05mm, then (if its all linear) a 500kg load will give a 0.5mm shortening....this is less than the elongation above, ie the spoke won't go slack.
Brandt's book is published 1981, so he isn't talking about modern deep rims?
You've made me dig out my copy of The Bicycle Wheel. On page 18 Brandt says the static load is about 500kg for a well tensioned 36 spoke wheel. He also states that it is dynamic loads which 'cause wheel deterioration and finally failure'. On page 29 he talks about the load affected zone, e.g. ~4 spokes for a 36 spoke wheel, and how 4 spokes tensioned to 100kg could support a 400kg load.

That leaves the question in my mind of how big a dynamic load a wheel might experience. I appreciate that would depend on variables such as speed, tyre width and pressure, bike/rider weight, and the size and shape of the hole or bump that causes the dynamic load, but I would have thought that an attempt to quantify the likely (range of) dynamic loads would be important in quantifying the likely effect on shortening spokes and rendering them slack.
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531colin
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by 531colin »

Sorry, I wouldn't know where to start quantifying the loads on a wheel.
However, we have some "herd experience" of what works, and also of what is problematical.

In the "problematical" camp we have (for example) 11 speed (130mm?) wheels with light, narrow rims and heavy, powerful riders.
Roger's 1: 2.2 tension ratio for these wheels is staggering; perhaps its no surprise that asymmetric rims offer some improvement?

I would be interested if anybody is in a position to compare the durability of say 10 speed 130mm/ 10 speed 135mm/ 11 speed 130mm/
11 speed 135mm/ with and without rim offset. You don't get much spoke hole offset on a narrow rim, but maybe its enough to compensate for the extra sprocket? I don't think spoke hole offset will be as much advantage as an extra 5mm OLN, but I don't have anything to measure.
I used to build many 8/9/10 speed 130mm wheels; I could build durable wheels for the big powerful guys by using a relatively deep stiff rim.

I question your figure of 70% lower tension.
8/9/10 speed Shimano 135mm rear wheels end up with 80 & 120 kgf (kilogram force) tension thats 1:1.5 ratio or a 33% reduction; regular (non-dynamo) front disc wheels are less dished that these.

I would put 8/9/10 speed 135mm wheels firmly in the "works" camp.
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531colin
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by 531colin »

pq wrote: 30 Jan 2022, 1:31pm When I build a wheel, if I think this is an issue I use thicker, single butted spokes on the drive side. I don't think there's ever any point using plain gauge spokes.
Spokes fail at the elbow due to fatigue.
Fatigue is considered to have 3 stages..........
initiation of fatigue crack
propagation of crack
failure
Of these, the initiation stage is the longest, and also the least predictable. (This is why you can get spokes failing over a long period in poorly built wheels....in this context "poorly built" really means poorly stress-relieved.)

So a thicker spoke at the elbow will take a bit longer for the stress crack to propagate to failure, but thats about all.

Single butted driveside spokes look right, but I'm not convinced they are a real advantage; if the wheel is not stress-relieved really thoroughly they are a disadvantage (as somebody said above) because they need more force to take a set.
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531colin
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Re: Wheels - how much dish before plain gauge spokes are advisable?

Post by 531colin »

rogerzilla wrote: 30 Jan 2022, 11:12am
Jamesh wrote: 29 Jan 2022, 10:20pm What's the ratio on a 8-10spd Shimano hub out of interest?

1-1.5, 1-2.0??
1:1.72 for the same wheel (I'm comparing DA 10 speed with DA 11 speed, but I doubt there is a difference for other groupsets).
8/9/10 speed 135mm Shimano rears get 80 and 120 kgf.....thats 1:1.5 ratio
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