Rear spoke patterns

[UpFromOne]

OK, time for a new discussion on an old, old subject.
Many light weight rear hubs are now being designed for a radial spoke pattern only, on the non-drive side (NDS).
My hypothesis is that this is an incorrect application of the physical dynamic forces in a cog-driven spoked wheel.
So I ask that this thread be limited to discussion rear wheel spoke patterns, as there will be plenty to discuss.

Objectives:
1. Since the hub flanges must be offset from the centerline in order to accept the cassette, the DS and NDS hub flanges experience different stresses. One goal is to equalize these flange stresses as much as possible.
2. Another goal is to equalize the spoke tension on each side, to better keep the wheel true.
3. Another goal is to equalize the stresses at the rim holes. (The pulling force from each side of the hub)

Assumptions:
1. A smaller (lower) hub flange experiences less stress than a high flange.
2. A longer spoke requires more tension than a shorter spoke to do the job (resist external forces on the wheel). that
3. More spokes on a hub side tend to result in more pulling force at the rim. Which is to say that fewer spokes under higher tension equal the force of more spokes at lesser tension.
4. We are discussing the pattern of radial on the NDS, and a crossed pattern (usually 2x) on the DS. For the sake of discussion and because of the design of these modern hubs, assume that each hub flange has the same number of spokes, regardless of the pattern.

Analysis:
The assumption in a crossed DS + radial NDS is that the torque force starting from the cassette will reach the DS flange more so than the NDS flange.
I don't agree. Modern hubs have enough material between the flanges, and are strong enough to almost completely resist torque equally at each flange.
Old-school hubs with a very narrow center section did exhibit this dynamic, but modern hubs have "cured" this issue with larger cores.

Now we deal with the spoke dynamics. Because of the offset, the NDS spokes are always going to be longer than the DS.
It appears that the radial NDS pattern is trying (among other things) to reduce the NDS spoke length. After all, a radial spoke is shorter than a 2x spoke. Combined with a 2x DS, this seems to be an attempt to equalize the spoke lengths used on each side, with the implied objective of equalizing spoke tension because of more equal spoke lengths.

The problem is that this only addresses spoke tension, without dealing with hub flange tension, or tension at the rim. A radial spoke, being shorter, will require less tension. Therefore, it aggravates the inherent difference in tension between the DS & NDS due to the uncurable offset.

This is further aggravated by the flange design, which is typically lower on the NDS. Again, I have to assume that this parameter is an attempt to cure the spoke angles. The narrower DS angle will be relieved with a higher flange, thus angling the DS spoke out just a hair more.
And a lower flange on the NDS makes those spokes angled in just a hair more. And, the lower NDS flange will lengthen the NDS spokes, thus demanding a hair more tension, which admittedly helps. But, using a radial pattern on the NDS is overall a shorter spoke than a 2x. So, the tension gain of a lower flange is actually dimished over using a 2x NDS spoke.

To cut this short, that is my issue. Using a radial NDS spoke actually results in a larger overall difference in forces between the sides. With the high DS flange /low NDS flange, use of 2x pattern on both sides will get the most out of that design. The use of a shorter spoke by using a radial pattern doesn't really gain anything, in my book, it makes the sides even more asymmetric in overall forces.

So these modern hubs designed only for NDS radial spokes (especially the straight-pull spokes with an even lower effective flange diameter) are missing the overall effect. If I had to have radial on one side, I'd actually rather have it on the DS (like ZIPP) than the NDS.

Flame on!

[Tommasini]

Your focus is on tension between drive and non drive side. But keep in mind that crossed spokes react to the dynamics of forces from the drive chain, in particular the lower tensioned non drive side crossed pattern has half their spoke recieve high tension from "pulling" and half recieve lower tension (goes slack) due to chain input ("pushing"). My experiance is most my nondrive side spoke breakage (which is rare) is with the spokes that go slack..... Solution, non radial spokes who all recieve similar input - non dynamic tension and then equal tensioning during the chain pull cycle. Now to the issue of radial on drive side and crossing on non............to me that's a pandora's box trying to deal with other issues

[Cyco]

Why will a radial NDS spoke require less tension?

The tension of any NDS spoke is what is required to correctly dish a wheel, and I fail to see how this is affected by crossing pattern

[über-goober]

Using a radial NDS spoke actually results in a larger overall difference in forces between the sides.

This is not true. You can put the numbers in spo-calc and see. No personal attack is implied here.. it's just the facts ma'am.

[UpFromOne]

All other parameters aside, a radial spoke is shorter than a crossed spoke. And, by a slight margin, it will sit at a greater angle to the rim, because its contact point at the hub is most direct. (A crossed spoke will attach at the hub off to one side and lower, relative to the more vertical radial spoke attachment point.) So as a shorter spoke, the radial will require less tension for its position than a crossed spoke.

And that is why I think that radial NDS spoking aggravates the tension difference on each side. (The "forces" I referred to are primarily spoke tension.) The fact that the NDS flange is smaller than the DS doesn't overcome that. That's why I conclude that radial NDS uses less tension than a 2x NDS spoke. Less tension on the NDS, no matter how it occurs from the design, is worse for the overall wheel integrity. Regardless of the NDS spoke length.

I'm not saying that radial DS is a good idea, either. I guess most of all I just don't agree with radial anywhere on the rear wheel.
I would also surmise that manufacturers offer radial-only NDS hubs because it looks cool, and decreases the weight of the hub and the finished weight of the wheel.
That seems to be a common motivation for current design and marketing trends.

I hope this clarifies my opinion that radial NDS does not result in better structural integrity. OTOH, please feel free to elaborate on this specific "spo-calc" conclusion, and the reasoning behind it.

[über-goober]

Here you go rocket surgeon:
http://sheldonbrown.com/rinard/spocalc.htm

[über-goober]

Did you plug in some numbers and compare? How did your opinions stack up to the Laws of Physics?

Backing up, for a modern 10/11sp rear wheel there's the following trade-off to address. Narrow flange spacing gets you good NDS tension at cost of poor lateral stiffness (eg American Classic 205) And wide spacing --given that the DS can only pushed so far toward the right until the chain goes in the spokes-- gets you poor NDS tension (eg White Industries for Campy). So you pick your poison; good hubs strike a balance (eg Shimano Dura-Ace or Alchemy ORC).

Your much-maligned radial NDS lacing actually provides the widest bracing angle, when laced heads-in. Next widest is your beloved 2 or 3 crossed, followed by radial heads-out. Having these different options is a good thing, so a wheelbuilder can use these tricks when needed. (The wheelbuilder should also know about the stresses radial lacing puts on some hub flanges, which is where you actually could type a reasonable anti-radial missive.)

And let me say that where's a hierarchy of importance, and bracing angles is right at the top of the list for what makes a well-designed wheel.

And then torsional rigidity. Yes rear wheels need to have crossed spokes on at least one side to prevent 'windup'. This can be overstated though. Millions of radial NDS wheels are doing just fine in the real world. Are we really going sit here typing about how we know more than the engineers at Mavic and Campagnolo? The smartest wheelbuilder I know, Jeremy from Alchemy, has radial heads-in NDS spokes on his personal bike.

What's least important? Look to your jive theories about the role of spoke lengths and 'angles to the rim'. You think having spokes cross gives them more tension or somehow makes them act more awesomer? Once in a while there's a shred of truth there, but it's a bee-farting-in-China effect on the outcome. We could rebuild a wheel with all the different possibilities and as long as the bracing angles were the same there would be no appreciable difference. If you don't believe the math, then you could look at a tensionometer.

BTW what is your wheel building experience? Where are you getting this information and why are you acting so stubbornly about it?

[Cyco]

All other parameters aside, a radial spoke is shorter than a crossed spoke. And, by a slight margin, it will sit at a greater angle to the rim, because its contact point at the hub is most direct. (A crossed spoke will attach at the hub off to one side and lower, relative to the more vertical radial spoke attachment point.) So as a shorter spoke, the radial will require less tension for its position than a crossed spoke.

A radial spoke attaches at the same point as a crossed spoke (as dictated by hub geometry) and has the same radial length as a crossed spoke. The ~5% length difference given by the longitudinal displacement for crossing will have no effect here, as the spoke starts and finishes at the same place.

And that is why I think that radial NDS spoking aggravates the tension difference on each side. (The "forces" I referred to are primarily spoke tension.) The fact that the NDS flange is smaller than the DS doesn't overcome that. That's why I conclude that radial NDS uses less tension than a 2x NDS spoke. Less tension on the NDS, no matter how it occurs from the design, is worse for the overall wheel integrity. Regardless of the NDS spoke length.

Maybe you should try drawing, or even perhaps building a wheel to see why über-goober, myself and many others disagree with you regarding your conjecture.

What caused you to come up with this idea?

[über-goober]

Anyone still awake? If so, here's some more wheelbuilding theory..

Maybe something to be learned from a wheel build i should have said no to:

White Industries (campy) 3x on a Mavic MA2.

Spo-calc shows how the NDS tension is 43%, and this was mated with a rim that will crack when you go much beyond 100kgf. So I used a threadlocking compound to prevent the nearly-slack NDS spokes from loosening in use. Also lighter guage NDS spokes, which should be more elastic throughout the wide range of tensions they will have to endure.

What else could I have done?
Some ideas.. I also could have:
-lobbied for 135mm spacing on the guy's bike.
-radial heads-out on the NDS. (Damn you crossed spokes!!)
-slipped a 2-3mm washer on the the L axle end and built the wheel with less dish (the "poor man's Alchemy hub").
-gone with Shimano spacing and a conversion cassette.
-used an offset rim

[Ypsylon]

Anyone still awake?

Yep. And so far I've learned that you have a cooler version of spoke calc than I do.

[Cyco]

There is more than one version of spo-calc? I have the same version as über...

[Ypsylon]

Actually, now that I double checke it, no.

I just remembered the "tension ratio calc" field in the lower right hand corner and had forgotten about the tension field next to the bracing angle.

I'm just a confused old man sometimes.

[UpFromOne]

Too bad that personal attacks seem to be unavoidable on these boards. My humblest apologies for presenting "jive" theories, and for "stubbornly" insisting that I know better than a revered professional wheelbuilder.

All I'm trying to do here is get some info on the issue: why are many high-end hubs being built with a radial-only NDS?

Where exactly is the benefit to the wheel as a whole, assuming that a wide bracing angle seems to be paramount?
(And if it were, then why the super low NDS flange diameter?)

I am not as reliant on Spo-Calc as others here, because whereas spoke length calculations are hard facts, spoke tension figures are only estimates because much depends on real-world parameters left out of the equation, like the spoke and rim materials being used.

But rather than elaborate on my own current understanding (which was only presented to drive the discussion, not to piss anyone off), what then is the plain and simple explanation for why radial NDS is, on balance, the best rear configuration.

[über-goober]

Upfromone,

Pleaseplease don't misconstrue anything I (or probably anyone else) wrote as being a personal attack. In fact all you need is $400 bibs to have full membership here in the club .

.
I will stop harping on this forever after one more sentence.

Which is: NDS tension is a fact of mathematics and not 'spoke and rim materials' or who is the builder or anything else. (And the bracing angle thing on rear hubs is a balance.. you can scroll back up to revisit my jive theories where I was saying all that).

Have a great weekend!

[Ypsylon]

While I might not vote for über-goober to become ambassador to North Korea, I'd like to remember everyone here of one of madcow's way not popular enough lines:

"This board and the world in general would be a much nicer place if everyone could just take themselves a little less seriously."

While the wording could have been nicer Über opposed your theory and I don't see that he intended a personal attack.

That being said, just closing my eyes and applying my limited physics knowledge I don't see where rim stiffness comes into play, as long as you don't have an asymmetrical rim that's stiff on one side and not on the other.