Wheel-building question: tensions on 26"=700c?

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rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

You'll never get all the tensions exactly the same. +/- 10% variation would be really, really good. You can help by buying a good straight rim to start with, using spokes of a very consistent length (DT are best at this in my experience) and taking the wheel up to tension very uniformly - so the threads just disappear, then one full turn, then maybe another, being sure not to miss any.

If you start with a bit of an egg due to uneven initial tensioning, it is much harder to fix it properly.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

rogerzilla wrote: 11 Apr 2021, 2:13pm You'll never get all the tensions exactly the same. +/- 10% variation would be really, really good. You can help by buying a good straight rim to start with, using spokes of a very consistent length (DT are best at this in my experience) and taking the wheel up to tension very uniformly - so the threads just disappear, then one full turn, then maybe another, being sure not to miss any.

If you start with a bit of an egg due to uneven initial tensioning, it is much harder to fix it properly.
Its so long since I did this on a daily basis that I had to get the tension chart out!
Front wheels are 100kgf (kilograms force), which is 21 on the gauge for a regular butted spoke (1.8mm centre)
Range was 20-22, ie 10% total. I think +/- 10% (19-23 on my gauge) is over-generous.
It always seemed to me that thinner spokes and higher tensions gave less variation in tension for a round, true wheel; I never understood quite why, but the tension always seemed to even out as you got up to final tension.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

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hoogerbooger wrote: 11 Apr 2021, 10:09am Am taking this all in. Despite Colin 531's sage advice, I've still managed to make a 700c Sputnik on 8 speed that's gone out of true. This clearly make me a novice. Was getting frustrated on Friday trying to true and get even tension and straight/round.

Is there a best way to go about re-truing a wheel that one deduces was built badly..........as us novices may do ?

(I decided to even up the tensions, rather than just true, as the ping-o-meter screw driver tap approach revealed a fair degree of uneven pitch. So I adjusted, using ping-o-meter, to even tension first( for respective sides) before truing. My ear is fairly good on pitch but when evened up I was rather surprised how far out laterally the wheel was. Then had fun with some nipples being much stiffer than others and one almost rounded nipple. The result is round and true enough but uneven tensions probably worse than before. ( stress relieved by gripping parallel pairs several times at end of truing))

( apols a little off OP I know)
Is the lacing correct? Have you bought spokes which are all actually the length it says on the box, or has some idiot been putting spokes back in the wrong box? (every bike shop has one!)
Do as Roger says.......back off all the nipples until the last bit of thread just appears out of the nipple, then tighten them up counting turns. (I don't muck about doing half turns...two full turns to start you off, unless the spokes are short)
Stress-relieving is a brutal affair, and the wheel will go out of true if you do it properly; because stress-relieving if you do it hard enough re-sets the elbow bend to suit where the spoke is in the wheel (inbound/outbound, etc.)
Get some tension on the spokes, true-ing a slack wheel is simply a waste of time.
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

If you have two brass washers under the heads (to compensate for thin flanges on ancient geared hubs), the creep, and loss of tension, on initial stress-relieving can be equivalent to a turn or two of the spoke key. The spoke heads dig into the washers as well as the bends sorting themselves out. I use an old crank wedged into the crossings to give the spokes a really good workout.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

rogerzilla wrote: 10 Apr 2021, 4:02pm I feel the spoke with my left hand while turning the spoke key with my right hand. I am feeling for the spoke "jumping" in the nipple as the threads break free, as well as wind-up. At an earlier stage, I do use the forced removal of wind-up by pushing on the floor (wheels of 26" or smaller can literally be stood on sideways if they are built well - it's a bit risky with 700c) but it's much better not to put the wind-up there in the first place, as this makes the exercise horribly iterative.

I have built a few entire track (dishless) wheelsets with Revs, and I nearly always use them for the rear LHS and front wheels. They make a very good wheel but the wind-up and the extra elasticity are a pain. A Rev can twist over 180 degrees before the spoke jumps in the nipple (I marked a few with a Sharpie once to test this) and the spokes affect each other more than Comps or, especially Champion plain gauge. BITD, as Brucey might say, racers used plain gauge because one broken spoke hardly affected the truth of the wheel, so you could keep going. The tension might be the same, but the strain (elongation) is very different. A Rev-built wheel is a wheel made from 32 very long springs, and is a much more finicky construction.
Wow, that seems a right pain. Is it worth it? Although as I put somewhere else, thin spokes and tight wheels always seem to me to equal more even tension. Have you tried spoke prep. or linseed oil, I wonder if that might make the threads smoother to turn? No harm in the threadlocking aspect after it has set, although probably not necessary with such a stretchy spoke?
I have built countless wheelsets with the "Spa special" spoking, ie. heavier gauge spokes driveside rear. (actually, done by Hewitt before Spa, and CJs favourite). There is no doubt you can build durable wheels that way, and a few big strong riders sought me out; but for several years now I have built all my own wheels with regular double butted throughout. I like the elasticity of the whole structure, and I'm sure that the load is shared among more spokes than it is with spokes like cartwheels. I understand CJs point that with differential thicknesses there is about the same stored stretch (thicker spoke with more tension vs. thinner spoke with less tension) so that if the spokes go slack at the bottom then the rim isn't pulled to one side; but if the rim is adequate for the load, and the wheel is tight, then the spokes don't go slack at the bottom; and the rim won't be pulled far enough to one side to take a set anyway, so I don't see the importance? And I don't think you need an extra thick elbow on DS spokes to prevent fatigue failure, because if you stress-relieve thoroughly they don't fail anyway.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

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rogerzilla wrote: 11 Apr 2021, 4:30pm If you have two brass washers under the heads (to compensate for thin flanges on ancient geared hubs), the creep, and loss of tension, on initial stress-relieving can be equivalent to a turn or two of the spoke key. The spoke heads dig into the washers as well as the bends sorting themselves out. I use an old crank wedged into the crossings to give the spokes a really good workout.
This is turning into a right wheelbuilding thread! I used to stress-relieve by Brandt's spoke-grasping method but since arthritis I have been stress-relieving by pushing down on pairs of spokes just above the last crossing on a big caster wheel viewtopic.php?f=5&t=110419&hilit=screwfix&start=15. Quite promising, but at 73 years old and 11 stone, I'm not much of a test!....I have never so far broken a spoke on a wheel I have built for myself, and I don't think I'll start now!
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

I soak the nipples in oil before I start building. It's messy but the nipple needs to be lubricated against the rim, as well as in its threads.

I usually do DT Competition on the RHS of a derailleur wheel and Revolution on the left. Revs are so stretchy that they are highly unlikely to go slack over a bump despite their lower tension.

I've only broken one spoke, on one of the first wheels I built 20 years ago. It was a no-name set of spokes recycled from another wheel, so I was pushing my luck. Even so, it lasted 18 years of fairly hard use, including two Dunwich Dynamos and my entire mediocre TT career!
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

I stopped lubricating nipples altogether. I don't find it necessary, and on NDS its probably counter-productive.
sarniacycle
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Re: Wheel-building question: tensions on 26"=700c?

Post by sarniacycle »

The above comments have provided a lot of material to chew through and learn from, thank you all.

While I'm trying to trust my instincts and limited experience, I also dug out an ipad that hadn't been switched on since 2015, managed (eventually) to charge it and to find and install the spoke tension-measuring app that PH suggested. It's good fun and together with this article (https://savetheneurons.blogspot.com/201 ... bably.html) comparing it with physical, spring-based meters, has helped to make sense of tension. Plus the app generates big digital numbers that look believable:

wheel gauge.jpg

I don't know what they mean, in practical terms, but they look interesting.

Does 81kgf make sense for a front 32spoked wheel? What is a kgf? For my rear 32 spoked wheel, I've got a pleasingly consistent 74kgf NDS and on the other, 118kgf DS. I've no idea what they suggest but they ping quite highly (DS) and a bit less highly (NDS). At some point I will put them on a bike and then, with or without teeth, I'll report back.
Last edited by sarniacycle on 14 Apr 2021, 9:30pm, edited 1 time in total.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

kgf = kilograms force....ie the spoke tension is the same as it would be if you had 81 Kg hanging on it (vertically, on Earth)
Average spoke tension to aim for (assuming a strong rim) is 100kgf.
So for a dished rear, it wants to be about 80 NDS and 120 DS
Fronts 100 both sides, unless disc wheel; which I can't remember, say 90/110?
sarniacycle
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Re: Wheel-building question: tensions on 26"=700c?

Post by sarniacycle »

Thanks Colin, this is great news. There's something reassuring about these numbers - especially in the current situation where it's hard to get a 2nd, hands on, opinion. Cheers!
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

Some rim manifacturers specify a spoke tension. Otherwise, use Colin's, but be prepared to adjust for rim construction. I probably go tighter than most people (> 150kgf on the RHS of a derailleur wheel) but I will scale this back if the rim has no eyelets (or single eyelets) or appears rather thin-walled.
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