Are stiffer wheels better wheels?

I haven't been burned at the stake in a while, so let's jump right in!

In customer conversations, a very often expressed preference is "I like nice, stiff wheels." And when I say it's phrased like that, it's always phrased like that. I'm going to do a post sometime about things that are always phrased like that (which will focus mostly on the tired tropes of equipment reviews, like how wide rims help tires "plump up," how wheels "spin up fast," and "hold speed well"). The next time after this that I feel like getting burned at the stake... 

This was a great kit design. Also, the day this picture was taken I did the last k of Smuggler's Notch either 4 or 5 times, twice with 40# of kettle bells in a back pack. These days, I need a rest day after having typed that sentence. 

We've done a whole lot of testing and writing about this in the past. And for the purposes of today's discussion we're limiting to wheels built for the uses that we primarily build for - road through light bondage XC MTB. Downhill and enduro wheels are still bike wheels and more similar than different to our focus, but excluding them might alleviate a bunch of noise.

Simply, my top line premise is that there is a line dividing "not stiff enough" from "stiff enough," and once that line is crossed, there is no further benefit to be had. The big "on the bike" tell for me is that an under built front wheel will steer badly. Put it into a hard corner and it doesn't want to turn. With all of the thinking about wheels while I ride that I've done in 10 years and lord knows how many miles, that's where I've gotten. 

It's long since settled that brake pad rub isn't caused by flexy wheels. That link is just one of a ton I could put up, but it's conclusive and representative of all of them. In general, Slowtwitch does great tech work.

The list of factors that affect wheel stiffness is also settled, but the world is still full of belief that spoke tension is one of them. It isn't. Simply, it is not. Once spokes are under tension and not slack, nope. 

From a wheel building standpoint, I prefer to replace "stiffness" entirely with "stability." As I learn about video recording, we'll put more of this into video form, but we torture wheels as we build them. The wheel is done when torturing it no longer changes it. It becomes stable. Some wheels can't reach stability. The AForce C25 disc rims could not be made stable at a spoke tension that would reasonably ensure against off side spokes going slack. Try building a 24h Stan's Crest (which they thankfully don't make), bring it up to tension, and then squeeze the spoke pairs hard. The rim flexes so much that when you take that squeeze pressure off, the wheel "re-settles" into a new shape. 

If you have a wheel that does that "re-settling" bit, then you wind up with some degree of what's happened to the wheel above. That wheel is not stable, which is within my concept of not being stiff enough. 

That trick of squeezing spoke pairs is something we do many times on each wheel that gets built, and there's a range of how much they move when you do it. An All Road 50 rear is clearly the most resistant to movement (what you would call "stiffest") wheel we build. They simply don't move when you do this. Cafe Racers are also in the same league. It's no coincidence that these are both carbon rims, and the two deepest rims we use. There are wheels that move quite a bit more than All Road 50s or Cafe Racers when you do this, but they return to stable. A Boyd Altamont Lite build, built to the same hub/spoke/spke count spec as a Boyd Altamont build, will exhibit quite a bit more movement. That proves the concept of rim dimensions having a big effect on wheel stiffness. That extra movement will be fine for some riders (my squeeze is certainly more load than a wheel sees in anything like normal use) but not for others, and that's the basis of our alchemy for determining appropriate spoke count. 

This simple trick is my quickest and probably best gauge on what works and doesn't. If they can't return to stable, they're no good. If they move a lot but return to stable, I'm not wild about it. And then there's a range of movement that makes me totally comfortable. And within that range, I am devoutly certain that those wheels are "stiff enough" and that more stiffness would be of no benefit. 

Spoke for spoke, a deep rim will be inherently stiffer and more stable than an otherwise similar but shallower rim. A Cafe Racer is slightly more stiff/stable than an RCG built the same way. 

The same rim built with more spokes will be more stiff and stable than if it is built with fewer spokes.

The same rim built with thicker spokes will be more stiff and stable than if it is built with thinner spokes. 

Hubs have a small impact on this, as well, but as we explored in withering detail recently, it ain't that big once you're using good hubs. 

Clear as soup, right? 


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  • Dave on

    Merton -

    Good question. If you take it on a spoke by spoke basis (that is to say, build a 24 hole wheel, and see which one is most stable), you can pretty much draw a straight line through depth and that will be the order. Or you could draw a straight line through weight and get to the same place. Weight and depth are basically in lock step, though HED is a tiny bit heavy for its depth, primarily because of slight added width.

    With added spokes, any rim can get there. Light and shallow rims with more spokes can be fine for heavy riders, but these oftentimes wind up heavier than wheels where you started with a heavier rim and fewer spokes. Aero would point to the heavier (deeper) rim and fewer spokes as well.

    And each increment of stability is not noticeable. It’s only if you go across a threshold where, for example, a 24h Altamont Lite would have stopped being stable enough and a 24h Altamonte would still have plenty in reserve. In almost all situations, once you have enough that’s enough and more is not better.

  • Merton on

    Just came across this, curious which alloy rim(s) you’ve built so far is the most ‘stable’, e.g. HED belgium, Easton R90SL, Velocity Quill, Aforce AL33, etc.?

  • Dave on

    Hi Steve -

    Of course the stability needed is different for a 130 pound rider than it is for a 240 pound rider. That’s the entire premise behind this statement above – <and then there’s a range of movement that makes me totally comfortable. And within that range, I am devoutly certain that those wheels are “stiff enough” and that more stiffness would be of no benefit.>

    One size fits all wheels generally aren’t optimum for a majority of people, which is why we’re able to be in the business that we’re in. More stiffness, to the point of unnecessary stiffness, is certainly preferable to not enough stiffness, as that would lead to instability. But there has never been any credible evidence of the power transfer phenomenon, and at the level where I am evaluating stiffness you sure aren’t going to be losing energy in wheel flex.

    If I could have a chart of each customer’s weight, max sprint, 1’ power, and 5’ power, tire type, % of time spent standing climbing vs seated climbing, typical road and terrain conditions, typical tires used and preferred inflation pressure, I’d love it and it would inform things much more than the typical “I’m this tall and weigh this much” basic info, but when needed we delve into it with people and get to the info that we think lets us arrive at the best build. It’s certainly not evident to me that anyone is doing a more complete job of unearthing, articulating, and applying these factors than we are.

    There is a clamor in the bike universe that “more stiffness is universally better and that’s that,” and I disagree. I’m not by nature an absolutist. There’s no evidence I’ve ever seen that supports this. My suspicion is that this is a close cousin to the long held tendency to overinflate tires because they “feel fast,” despite being measurably slower.

    This old post by Roues Artinsanales in France includes info from a Mavic test done a long time ago which well supports my “beyond enough, more is not needed” position. http://www.rouesartisanales.com/article-23159755.html

    Plus, at the end of it all, I’d be willing to be that wheels we build wind up near the top of the pile for appropriate stiffness to customer need ratio anyhow. We’re not arguing for less stiffness, we’re arguing against the “more is always better” dogma.

    Thanks

  • Steve on

    Dave, Reading, enjoying and admiring your prolific and informative burst of blogging!

    My comments/questions regarding your key sentence above – From a wheel building standpoint, I prefer to replace “stiffness” entirely with “stability.”

    For me, from a wheel rider’s standpoint, stability should be a minimum requirement. I wouldn’t want to buy a wheelset that isn’t stable the same way you wouldn’t want to sell me one. But wouldn’t a wheelset that has less “movement”, aka is “stiffer”, transfer your power more efficiently to the road because there’s less loss in moving it, all else being equal, than one that has more movement yet is still stable, assuming the rider has enough power to move it? If so, isn’t there indeed more benefit for some riders to be had from a “stiffer” wheel?

    The question then becomes, at what power output is the wheel “stiff enough” and therefore the spokes, hubs, rims, and their combination are selected to create it such that the rider can’t move it? One wheelset might be stiff enough for me if I’m 143 lbs putting out 250 watts on a climb or 500 watts in a sprint but not stiff enough for you if you are 187 lbs putting out 400 watts on a climb and 900 watts in a sprint.

  • Catherine on

    “Stiff” for me means the wheel is resistant to braking or warping. Roads here in new England are complete crap and while most drivers are considerate, it’s not unknown to be forced into potholes or over sticks and such. Wheels which warp are no bueno!

    I’ve ridden CXP-30s (loved them!), Cosmics and now Cafe Racers- so far never lost a spoke, never had to true wheels or had any sort of failure. The more spokes and thicker the rim maybe? Weight is a whole lot less important to me than not being stuck out in the boonies with a broken bike.



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