Hub geometry for strong wheels part deux

Yesterday's blog set the table and laid out a few definitions. Today we'll spend some more time talking about two words (strong and stiff) and try to bring some closure to this question. We might not get to full closure. 

First let's put that sexy beast of a geometry chart up again...

A note that I didn't include yesterday is that these figures are all done with an RCG36 rim as the basis. If you use a deeper rim, the bracing angles will improve, while a shallower rim would make them worse. The RCG36 is a nice middle ground rim to use for this illustration, and please note that though the bracing angles would change, no hub's relative ranking would change.

As you can see, there are a few ways to skin the cat and still wind up in a similar place. Chris King pairs moderate flange spacing with large flanges and winds up in a good place, while Industry 9 winds up in almost the same place with smaller flanges and wider flange placement. Onyx has the lowest bracing angles, which would probably see it become the build with the most deflection of this bunch were we to fire up the deflection tester again. But look at its tension ratio - 66%. That means that if we put 100kgf average tension on the drive side spokes, the average non-drive side spoke tension would be 66kgf.

It's a pain in the butt, but testing wheel deflection (most people's common reference for "stiffness") is doable. 

So does this make a wheel built with an Onyx hub "absurdly strong?" No, not compared to any of the others on the list, at least under any definition of "strong" that I can think of. What it does accomplish is that the non-drive spokes have higher tension. This "reserve tension" helps those spokes to avoid the cycling fatigue that we talked about yesterday. All else being equal, the Onyx-hubbed wheel would be the last to break a non-drive spoke from under tensioning, which certainly has value but it wouldn't inspire me to call that the compelling strength metric.  

In the other direction, we have I9 Torch hubs with a 7.4º non-drive side bracing angle (which is the primary driver of a wheel's stiffness, or deflection resistance, which you can read all about here - and that page might take a hot second to load through an error message). Does this make I9 Torch-hubbed wheels absurdly strong? No. It means they will be the most resistant to lateral deflection among the wheels on this table, all else being equal. 

The primary thing that this all tells me, from a quantitative viewpoint, is that all of these hubs designs wind up giving fairly similar wheel characteristics. The Onyx and I9 hubs, despite being at opposite sides of this cluster, aren't going to build wheels that are totally appropriate for one rider/use and totally inappropriate for another. Built well with good complementary components, they're all going to be good wheels. 

I used to say that when I built wheels, I took the drive side (rear) or disc side (front) to an appropriate max tension, and then let the other side be what it was. Now I've kind of flipped that in my mind, and think of getting the off side spokes up to an appropriate minimum, and let the on side spokes be what they are. For rear wheels, I like to have the non-drive side up into the mid to high 60s of kgf, which as you can see would normally have you at about 120-ish on the drive side. For front wheels, the tension ratios are more even, so you might get 80kgf on the off side with only about 110kgf on the disc side. That's plenty of reserve tension in both cases, without risking over tensioning issues on the on side. 

So what's a stiff wheel? Simply that's a wheel that has less lateral deflection. Torsional stiffness is a factor, but it's very difficult to measure and the measurements that I've seen done don't show a big range of values. How much stiffness a wheel needs is subject for debate. Too little and the wheel will behave badly under torque, a flexy front wheel will understeer, and too little stiffness would leave a wheel prone to cycle fatigue and ultimately to failure. I do not think that more is always better. Internet forum ninnies seem wildly obsessed with more is better, and by now you should know where I am on that. 

Okay we didn't get to "strong" because I have writing fatigue and need to build some wheels now. So this just became a three parter. 

 

 


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  • Dave on

    There have been a few “neutral tension” wheels that I’ve seen – Spinergy Spox, Mad Fiber, the original Spinergy 4 spoke wheels… None of them are in any sort of broad use anymore. Spinergy 4 spokes and Mad Fibers had construction issues that probably never let them prove or disprove the concept of the spokes. The Berd ones are interesting, and by interesting I mean I will happily let others play with them. I have enough of the base material (dyneema string) in stock and in use (front sailing) to make a few dozen wheels. The material itself is super strong – a 3mm diameter string could easily pick up your car. The things that hink me out about them are 1) material creep. When we make forestays (the front shroud) out of this stuff, it has to settle over a bunch of days of use and then it keeps on growing a little bit over time 2) the connection between the metal part and the fiber part gives me the willies and 3) holy cripes the time it takes to lace is outta hand. So you pay like $6 or $8 a spoke or something like that and then we’d charge probably $300 on the build and pray not to lose money on it. Titanium spokes are proven not to be good – they’re too elastic and I think they had breakage problems, plus the corrosion with nipples was high high high. There are some new carbon spokes out these days. Sapim took a stab at it and bailed. I don’t know, we’ll see.

    Stainless spokes do a VERY good job against all parameters. I’m all for innovation but I love me some steel spokes.

  • C Mac on

    I usually get cycling fatigue on lap 2 of a crit

    I love these tech seminars – gives us something to think about once we’ve been dropped with another hour to get home

    You mentioned the “can’t push with a string” concept with the dental-floss-on-a-flag-pole example: Since steel spokes do get to resist tension and compression, do you believe fiber-string spokes (some examples out there but never seen with my own eyes – https://gearjunkie.com/berd-bicycle-spokes-soft-uhmwp-polymer ; https://pirope.net/) are dead on arrival? While we’re on the topic of linear tension and compression, does carbon (or titanium or whatever) have any advantage over 18/8 stainless in the strength(durability)-stiffness-weight equation?

  • Keith Baumgardner on

    👍stuff


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