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

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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

rogerzilla wrote: 8 Apr 2021, 9:00pm A pringle is generally elastic and will vanish if you slacken each spoke about half a turn. It is basically Euler buckling in a ring rather than a column - the rim is trying to get out of the way of the compressive load. The narrower and lighter the rim, and the smaller the box section, the more likely it is to pringle.

To get a permanent pringle, you really have to be going for it!
Yes, a rim doesn't take a set when it pringles....back off the tension a bit, and it flips back to straight.
In a crash where the wheel gets a large side load, you can get a superficially similar-looking wheel, with 4 big waves, 2 left and 2 right, but with some spokes slack...then the rim has taken a set, and its pretty difficult to get them back to a condition which will get you home, never mind last a week.
Valbrona
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Re: Wheel-building question: tensions on 26"=700c?

Post by Valbrona »

rogerzilla wrote: 8 Apr 2021, 9:00pm A pringle is generally elastic and will vanish if you slacken each spoke about half a turn. It is basically Euler buckling in a ring rather than a column - the rim is trying to get out of the way of the compressive load. The narrower and lighter the rim, and the smaller the box section, the more likely it is to pringle.

To get a permanent pringle, you really have to be going for it!
But what does pringling look like for a novice like me?

Thanks.
I should coco.
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Chris Jeggo
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Re: Wheel-building question: tensions on 26"=700c?

Post by Chris Jeggo »

+1
sarniacycle
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Re: Wheel-building question: tensions on 26"=700c?

Post by sarniacycle »

PH, thanks - that spoke tension gauge looks really fun. Have you seen this (long) discussion, comparing it with various mechanical tensionmeters? https://savetheneurons.blogspot.com/201 ... bably.html

Conclusion: "The Spoke Tension Gauge app is a winner in the absolute accuracy and a close second in the reading accuracy. It is also far and away the cheapest..."

Sadly, I have an android phone and think it's only available for iphones, so will continue with James's pingometer, even cheaper...
iandusud
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Re: Wheel-building question: tensions on 26"=700c?

Post by iandusud »

sarniacycle wrote: 8 Apr 2021, 10:43pm PH, thanks - that spoke tension gauge looks really fun. Have you seen this (long) discussion, comparing it with various mechanical tensionmeters? https://savetheneurons.blogspot.com/201 ... bably.html

Conclusion: "The Spoke Tension Gauge app is a winner in the absolute accuracy and a close second in the reading accuracy. It is also far and away the cheapest..."

Sadly, I have an android phone and think it's only available for iphones, so will continue with James's pingometer, even cheaper...
I don't think you have told us what use the wheel is for and what components you have in mind using. This is relevant. As Colin has pointed out using very lightweight narrow rims on highly dished wheels makes the question of accurate spoke tension more critical (same is true of low spoke counts).
sarniacycle
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Re: Wheel-building question: tensions on 26"=700c?

Post by sarniacycle »

Thanks iandusud
The 26" wheels I thought of using as a guide, tension-wise are 32h Zac 2000s, 3 cross.
The 700c ones are a 32h Kinlin 31RT rear (the offset version) and a 32h Ambrosio P20 front, 3 cross again, both relatively strong and reasonably wide rims, I believe. I've laced these up and am about to tension. Really I'm interested in understanding tension a bit more - what people do and how it works. If It were legal, I'd be out and about squeezing people's spokes to get a sense of things.
The 26" set I use for touring/about town/shopping on a Thorn. The 700s will be on an audaxy Dave Yates for fun/longer day trips/lighter overnights.
Cheers, Adam
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

Even with an offset rim, an 11 speed 130mm 700c wheel is a very different kettle of fish to a 7 speed 135mm 26 inch.
I retired from Spa long before they started with Kinlin rims, but that Kinlin 32RT https://spacycles.co.uk/m20b0s116p3832/KINLIN-XR-31RT looks like a pretty sensible rim. 30mm deep, width is 19 internal, 24 external.
You shouldn't be pringling that in a hurry!
I didn't find max. recommended tension https://kinlin.com.tw/xr-31rt/
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

I built a 20", 28 p/g spoked wheel on a very stiff Exal TX19 rim today. Now that's an easy one - next to no spoke twist to deal with, minimal dish and came true in a pop. The hardest bit was threading 2 x 8BA washers onto every spoke, because it was an old thin-flanged Sturmey-Archer hub.

I use a lot of DT Revolution spokes on 700c wheels. Now they are time-consuming, which is why some shops won't use them.
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531colin
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Re: Wheel-building question: tensions on 26"=700c?

Post by 531colin »

rogerzilla wrote: 9 Apr 2021, 9:01pm .......I use a lot of DT Revolution spokes on 700c wheels. Now they are time-consuming, which is why some shops won't use them.
a bit more wind-up?
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

Yes, more than you'd think compared to DT Competition, although it's only 0.3mm difference in diameter. Twice the twist, in fact.
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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, 1:34pm Yes, more than you'd think compared to DT Competition, although it's only 0.3mm difference in diameter. Twice the twist, in fact.
I don't understand why a bit more wind-up makes a significant difference to the overall time/difficulty of a build?
My way of working was; align all the nipples the same so the key goes straight on without fumbling; to tighten/loosen a spoke go "past it and back a bit" to get rid of wind-up......my guess is we all do similar?
When built, true, round, stress-relieved, tight and even tension, my final repeating cycle was..stress the wheel, true the wheel, balance the tension; repeat until you have a wheel which doesn't "settle" when you stress it, with an acceptable compromise between trueness/roundness and tension balance.,,,this also gets rid of wind-up.
"stress the wheel" in this context means put the axle end on a lump of wood on the floor; grasp diametrically opposite points of the rim, and put a significant proportion of your body weight onto the rim; go all round the rim,turn over and repeat.
A significant proportion of your bodyweight means that (with anything approaching a light rim) you can feel the difference in stiffness either side of a dished wheel.
Once you can do that to a wheel without it "going off" you can be confident that you can post it out to a customer, and it won't "go off" when they ride it.
rogerzilla
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Re: Wheel-building question: tensions on 26"=700c?

Post by rogerzilla »

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

Post by hoogerbooger »

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)
old fangled
Jamesh
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Re: Wheel-building question: tensions on 26"=700c?

Post by Jamesh »

I tend to get it straight first and then tension.

Using half a turn per spoke until I get the tension about right.

Cheers James
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