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Old 03-06-08, 06:39 PM   #1
eriksbliss
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Lateral Stiffness in Wheel -- Do I Care?

I'm hoping that I can inspire the hard-core BF physicists or other techophiles to give me thoughts on this stiffness-related question -- I don't want to get Waterrockets steaming again before his long-planned frame tests are done, but . . .:

I am considering a new set of carbon wheels, which in the few tests I have seen exhibit more lateral flex under a given force than many of thier competitors -- in other words, the wheels do not test well for what I understand to be called "lateral stiffness." They test better than their competitors, however, for aerodynamics. They are also cheaper than many competitors.

Assuming (a) that the wheels don't flex so much that they rub on anything (like brakes or stays), and (b) that I don't care about "feel" (assuming that I could discern the flex), what difference does it make? Does a lack of lateral stiffness correlate to less speed? From start line to finish line, is there a disadvantage due to the trait of the wheels?

(Basically, I am damn near convinced that I want to buy these wheels, and am only sweating the flex issue, and trying to convince myself that it is no big deal.)
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Old 03-06-08, 06:41 PM   #2
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Originally Posted by eriksbliss View Post
Assuming (a) that the wheels don't flex so much that they rub on anything (like brakes or stays), and (b) that I don't care about "feel" (assuming that I could discern the flex), what difference does it make?
None.
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Old 03-06-08, 07:23 PM   #3
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You're a bit vague in these wheels you speak of - which brand/model are you referring to that is more aerodynamic than competitors, "cheaper" than competitors, yet not as laterally stiff as its competitors?
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Old 03-06-08, 08:40 PM   #4
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I think I contributed to your worry...

If you don't care about how they feel and aren't getting into any of the relatively uncommon handling situations that I described where I don't like them, they're fine wheels.

If the wheels are the ones you mentioned before, don't forget that despite my comments, a pair of them is still my primary race wheelset on the track (and I can afford to get different ones if I want).

And I'm a physicist.

Where do you ride?
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Old 03-07-08, 05:12 AM   #5
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I've ridden some wheels that are more laterally flexible than, say, a nice, high flange, 32h wheel. I think you'll be fine for most racing/riding.

RevX plain, TriSpoke, Mavic Cosmic Carbon (first gen), HED disk, Zipp 440 with 16 spokes.

I raced on all but the disk and Mavics. I found them to be perfectly fine in crits and stuff, esp the ones with high sustained speeds. I used TriSpokes for a few years after watching Coors Light dominate the Tour de Michigan while riding them in every single race, even a gusty, windy, 8 turn, 1/2 mile crit course. I figured if they could do it, I could do it.

I've since moved to slightly stiffer wheels (superstiff RevX with x braces and now Reynolds DV46). I liked the RevX better when it didn't move left-right as much (the rim was stiff but the spokes were not - so instead of flexing halfway up the rim like most wheels, they flexed by tilting left right around the hub). The Reynolds are simply the lightest aero wheels I've ridden and I like them a lot - they jump and sprint nicely, except I want to relace one front wheel with round spokes as I don't get along with bladed ones (can't hold a straight line when sprinting).

I have no proof of anything (even that the wheels are more flexible) but I raced the various wheels probably 3-5 years minimum each and trained on them as well.

cdr
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Old 03-07-08, 11:00 AM   #6
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Partly depends on what you're going to be doing with them. Crit racing, Sprinting, and high speed mountain descents, I think you definitely want a laterally stiff wheel.

At what point is it stiff enough, would be the question.
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Old 03-09-08, 03:29 PM   #7
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You're a bit vague in these wheels you speak of - which brand/model are you referring to that is more aerodynamic than competitors, "cheaper" than competitors, yet not as laterally stiff as its competitors?
Hed3s: from the data I've seen, they have about the best aerodynamics out there, but are on the high side for lateral flex. And based on my own shopping experience, I can get them cheaper than anything comparabale by Zipp or Mavic.

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I think I contributed to your worry...
Don't sweat it, Duck -- you peaked my interest, but then I followed it up with some research, and the objective data shows the flex you spoke of. I also found plenty of other posters (on FGF) who ***** about them much more than you do.

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Partly depends on what you're going to be doing with them. . . . Sprinting . . . I think you definitely want a laterally stiff wheel.
Track riding. I posted here, rather than in the track forum, because that forum has minimal traffic, and I figured lots of road racers would be hip to my issue -- and the concerns from road to track are not too different, to my guessing.

By the way, here is the "official story" from Hed (to whom I posed some questions):

"H3s are as stiff as a 32 hole traditional wheel. Odd flex only comes from one of two ways.

First, discs and H3s are stiffer from the hub edge to the tire - very stiff. If you can flex the wheel, it comes all the way from the hub. This can make for enough movement to bring the rim over to the brakes if you run your brakes tight. The wheel is stiffer overall than a spoked wheel, and more efficient, but what flex there is comes from a different place in the wheel. We had this problem with making discs for Postal, and with one rider in particular ( he won the tour a few times). They kept asking for stiffer discs, so we kept making the sides stiffer. After a few, when they were still asking for more stiffness we took a very close look at the wheel and found that the hub was where the flex occured. We can't reduce it without adding a lot of weight to the hub and recutting the molds. Since the wheel is still stiffer than others, we will not make changes because of the added weight.

The second case when an H3 is flexy is when it is worn out. Again we are talking about flex at the hub, but in this case the bond between the hub and carbon is compromised and the wheel is noticeably flexy when you get out of the saddle. In this case there might be enough flex under a powerful rider to bring the tire to the chainstay. There is no visible indication when the wheel is worn in this way - it can still be ridden.

I expect H3s to last at least 10000 miles, I've seen them go more than 30000 miles. wearing out is rear only, I have never seen a front do this."

I'm inclined to give them a try -- that is, Hed3 front and back on the track bike -- and if they flex too much, I'll sell them (as "nearly new!").
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Old 03-10-08, 09:34 AM   #8
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you can also flex a wheel while climbing. recently I was away from home and
rented a caad9 with mavic ksyrium elites. during steep climbs out of the saddle the brakes were
rubbing. I'm sure it wasn't the frame as it is caads are extremely stiff.

for what it's worth I have a set of spinergy stealth 45mm carbon clinchers, not the lightest wheels but a good deal and very stiff and aero.
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Old 03-11-08, 03:59 AM   #9
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I'm 190 lbs of bike beating badness. Stiffness is everything.
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Old 03-11-08, 08:24 AM   #10
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I might as well post here what I did over in the track forum and in PM-- the only time I've had a problem with them is in a madison on a steep-ish concrete track. If your technique is a little sloppy and the bars turn a little while you're putting your partner in (happens worse when he comes in too slow), you can get a very scary resonant wobble in the front. I've only had it happen a few times, but it was a bit disconcerting. I've ridden them in madisons on flat tracks without problems, and on ADT, with most other parameters the same (e.g. same partner, same bike). And I'm 180-185 lbs of endurance track rider (i.e. road sprinter).
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