Spoke Tension

Spoke Tension

I don't know how to explain it, maybe cycling forums are behind it, but we often get a bunch of questions about a specific topic all at once. The current one is whether we tune wheels to riders using spoke tension. The answer is simply no. We're not big Tweeters, but we did Tweet an explanation, which seemed to strike a chord. The thread is as follows:

1. There is a correct amount of spoke tension in a wheel. That amount of tension is called ‘enough.’ It’s not the same for every build as some builds can’t take or don’t need as much as others. Once ‘enough’ has been applied, more has no benefit.

2. Too much causes problems when the wheel gets overloaded and endangers components. Not enough means that spokes go slack with cyclic loading and will prematurely break. Once a spoke is in tension, more tension adds no stiffness or strength

3. You can not tune ride quality with spoke tension. You do that with components and, to some degree, spoke count. Mostly you tune ride quality with high quality tires at correct pressure. Thank you for coming to my TED talk.

Modern mountain bike wheels, with Boost spacing and often using offset rims just don't need very much tension. Strong carbon rims like the Hotfoot can take a ton of spoke tension, but because you have fairly equal spoke tensions on both sides of the wheel, there's little chance of spokes going slack in a well built wheel. The max we shoot for in a Boost-spaced mountain bike wheel is about 110kgf on the loaded side. 

Rims like these old school Rigida rims - pencil thin and no deeper than the brake track, made of reasonably soft alloy - just plain can't take enough spoke tension to be built into 11 speed road rear wheels. The dish (angle split between the drive and non-drive side spokes) means that the drive side spokes need to have +/- 130kgf in order to have my safe minimum of 65kgf on the non-drive side. These rims don't survive getting built with that much spoke pressure - they get REALLY unstable - so they are best left to classic builds that use less dish. Even still, they're marginal - these old wheels require a ton more truing maintenance than the "none" that our typical builds require. They're also prone to spoke tension drop when you install tires on them. The wire bead tires that these wheels got don't affect tension too much, but try to put a tubeless tire on them and the spokes would turn into overcooked noodles. 

These deep section Rail 55s can take an absolute heap of spoke tension. The deep carbon rim just takes it and takes it with no consequence. 11 speed (and higher, now) drivetrains require a good fair bit of tension on the drive side to enable a high enough tension on the non-drive side, but even going up to 130kgf on the drive side, these wheels laugh it off. Since they are so stable and not subject to much tension drop, you don't need more (back to my "enough" statement in the Tweet) but what you do need, you can very safely get.

Note that this issue is different from wheel stiffness, which is overwhelmingly produced by bracing angle, spoke count, and spoke gauge (thickness). Be ready to fall over in your chair here... I'm ready for at least gravel Boost if not road Boost. We've seen some rims that we'd completely written off for kind of "normal" use (Stan's Crest, as an example) come alive when used wide hubs with less dish (a set of single speed Boost wheels we built, for example). The two sets of Hotfoot wheels we're shipping today, you pick them up and you're like "no way is this an all-mountain capable set of 29er wheels" - they feel that light. And yet they're just tractor strong. So with a big change for the good in hub bracing angles, man you'd have some leeway to do some crazy light and yet still fully strong builds. There are a lot of other factors to consider there, but as the wheel builder this is what I'm selfishly focused on. 

Slightly related to this, I've been doing a ton of riding on my mountain bike, using gravel wheels, on all kinds of different surfaces. Mostly road, as mud season is a real deal thing in Vermont and I'm slightly over it. And it's quite slow compared to a road or cross/gravel bike using the same tires and wheels. The pedal stance is much different (wider), which stinks for me. And the momentum is really different in a bad way as well. There's an almost 8 mile generally gradual but sometimes steep climb close by, and I'm sure you'd just sail up the thing on a road bike but on the mtb you just get absolutely bricked up sometimes. I see the power that it's taken people I know who are about my size to go up it 7 and change minutes faster than I've done, and this is power that I can easily do for a half hour. It's hard to tell if drafting is a factor, so there's that. But it appears that there's a ton in there, somewhere. Alas, this is the bike that lives here for now, it's very fun to ride,  and you will not hear me complaining about the riding around Woodstock. It's world class. 


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1 comment

The Woodstock area has great riding, and a lot of great country stores! Enjoy!


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