2012 velo mag aero wheel shootout

Discuss light weight issues concerning road bikes & parts.
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WMW
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by WMW

Good test Caley... your articles on VN are top notch!

I have a couple of comments though:

The Enve wheels appear to be custom builds with White Industries hubs... this is not a set offered by Enve, and they are heavier than any of the stock Enve builds. I thought something was funny when the Enves had high weight, but lower inertia... implying light rims, but heavy hubs.

The "control" wheels (32 hole DT Swiss RR 415 laced 3-cross to Chris King hubs and mounted with 25mm tires) are a good selection if you want a set with the highest possible aero drag, but IMO it would be more interesting to have the control be a better aluminum rimmed set... something like the new Kinlin 23Wx28D rim with CX-Rays in 20f and 24r (like the Boyd Vitesse) with 23mm tires, so that people could see how much is really attributed to the deeper carbon rim. Maybe then the other manufacturers would opt out too, in addition to Zipp?

21mm tubulars are used... aren't these smaller than what would typically be used on wide rims?

It's sad that manufacturers can just opt out. Zipp always allows Tour to test their wheels though... I wonder why? They do tend to win those, also...
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by Weenie


NGMN
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by NGMN

WMW wrote:21mm tubulars are used... aren't these smaller than what would typically be used on wide rims?


Rruff, the article states in the section on "Tire Size" that 21mm was on average, fastest for all wheels. Definitely seems like one of those places where you make a single choice and go with it, rather than try to present three different data sets and then put that in to the data presentation.

Also, Zipp still recommends their 21mm tire I believe for the fastest setup on FC wheels.

p.s. I'm not from Velonews. I love the suggestion of the 23x28 rim being included.

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WMW
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by WMW

It makes sense that the 21 is the fastest... or at least the aeroist (Crr will be higher), but these are road racing wheels, not TT. And I doubt many road riders will opt for 21mm tubulars on these wide rims... but I could be wrong.
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by VNTech

HammerTime2 wrote:Can you comment on the aero impact of 25 mm in rear vs. 23 or 21? Is a 25 mm in rear with a 23 mm in front "significantly" (purposely ambiguous) worse aerodynamically than 23 front and rear? Does the width of tires (front or rear) have an effect on crosswind stability?

How does crosswind stability of 6.7s compare to low profile round spoke wheels? To 3.4s? To what extent does rider weight affect the assessment of crosswind stability?



We didn't do any testing with different front and rear sizes. Tunnel time is pricey, after all. Had to keep it limited.

The 6.7's will still kick you around more than a traditional wheel. But, unlike the old V-shaped stuff, you can ride them in pretty nasty crosswinds without any real issues. We get very, very strong winds in the spring (usually a day or two with gusts up to 130kph, and lots of days of 50-60kph+). Normally I don't ride deep wheels much at all in the spring, but both the 6.7's and Hed 6's were fine up to about 40kph crosswinds.

HammerTime2 wrote:And now in the category of always wanting more, have you considered evaluating some wheels not marketed as aero by the same methodology - of course, for wheels lighter than Bontrager, you'll have to change the weight score formula (maybe just go up higher than 5?)? In particular, it would be nice to see Enve 3.4s, non-Smart Enves, MadFibers, and Lightweights (Standard/Oberymayer and Ventoux) evaluated in this manner. Even if they're not being sold primarily on their aero attributes, it's nice to know how aero they are, stability in crosswinds, etc. Might some manufacturers not want to participate for fear of not looking good?


We don't have a pressing reason to evaluate wheels that are sold without aerodynamic claims in the wind tunnel. It's expensive, which is why we're one of just a few mags in the world that do it. The purpose of this test was "if you want the best aero wheelset, which should you buy?" It's pretty clear that Lightweight, old V-shaped wheels, etc are probably not it...

Although I do agree that it would be interesting to compare, it doesn't make a whole lot of sense for us to do it.

For the question about tire size used, it was just a way to normalize. We tested each wheel with 21, 23 and 25mm, actually, and the ranking was identical. But with minimal space in print, we weren't going to publish all those charts.

And yes, you are correct regarding the Enve wheels and WI hubs. When we first received the wheels they were offering those hubs.
VeloNews Magazine/VeloNews.com tech

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djconnel
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by djconnel

Thanks for posting that link! Impressive aero results by Enve.

One bone to pick:

"mOrE ImpOrtant than wEIght — rOtatIOnaL InErtIa"

(hmm... I coped and pasted from the article).

Anyway... Bzzzzt! I disagree except for flat criteriums with sharp corners. On rolling terrain more rotational inertial actually (microscopically) helps maintain momentum, which is good.

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by Epic-o

djconnel wrote:Thanks for posting that link! Impressive aero results by Enve.

One bone to pick:

"mOrE ImpOrtant than wEIght — rOtatIOnaL InErtIa"

(hmm... I coped and pasted from the article).

Anyway... Bzzzzt! I disagree except for flat criteriums with sharp corners. On rolling terrain more rotational inertial actually (microscopically) helps maintain momentum, which is good.


From a muscular standpoint, reducing accelerations could be positive but from an energetic one, if you consider two different speed functions with the same average speed during a period of time, the one with the minimal integral of its cubic power in this period of time is the more efficient way to cover that distance.

The question is if a more constant speed translates always in a lower value of that integral and, consequently, less work to overcome aerodynamic drag

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prendrefeu
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by prendrefeu

Epic-O,

Could you translate the first sentence of your reply into layman's terms?
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Epic-o
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by Epic-o

prendrefeu wrote:Epic-O,

Could you translate the first sentence of your reply into layman's terms?


Simplifying, there are two dissipative forces when riding in level ground, rolling resistance and aerodynamic drag. Work is the integral of power.

Rolling resitance power depends linearly of the speed, this means that if you travel from point A to point B at the same average speed, the work needed to overcome this force is independent of how the speed changes.

Aerodynamic drag power depends of the cubic power of the speed so work done to travel from A to B isn't independent of how the speed changes for the same average speed.

The speed function depends of how the cyclist delivers his power and the mass and inertia of the system

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strobbekoen
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by strobbekoen

The energy required to overcome drag is corresponding (not equal to) to the cubic speed (if there is no wind).
So if you imagine the speed curve of a ride, the total energy (work done) to overcome drag is corresponding to the surface under (integral) the curve of the cubic speed (v³). Question he asks is if that surface is always smallest with a constant speed or a variable speed.

If there is wind speed, The energy required to overcome drag corresponds to groundspeed * (groundspeed+airspeed)²
airspeed being positive for headwind, negative for tailwind.

However, rolling resistance corresponds to the ground speed, not the cubic of the ground speed.

edit: sorry epic-o, was writing this while you posted yours. :D

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HammerTime2
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by HammerTime2

Ignoring the transient effect at the beginning of a ride, and assuming constant wind, constant surface, and no hills, then indeed, that constant speed uniquely minimizes energy required for a given average speed, is immediately apparent from Jensen's inequality http://en.wikipedia.org/wiki/Jensen%27s_inequality , on noting that the integrand consisting of a positive coefficient linear term plus positive coefficient cubic term is a strictly convex function.

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by Epic-o

HammerTime2 wrote:Ignoring the transient effect at the beginning of a ride, and assuming constant wind, constant surface, and no hills, then indeed, that constant speed uniquely minimizes energy required for a given average speed, is immediately apparent from Jensen's inequality http://en.wikipedia.org/wiki/Jensen%27s_inequality" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; , on noting that the integrand consisting of a positive coefficient linear term plus positive coefficient cubic term is a strictly convex function.


I'm not sure that this is applicable here, the cubic power of the speed evolution of the cyclist isn't convex. In any case, the constant speed case is out of the question because the variable power that a cyclist generates makes the speed highly oscillant.

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HammerTime2
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by HammerTime2

HammerTime2, please consider this a formal warning for your language.

There was no need for it, it's also not the first thread where you have been in where we have requested conversation have a semblance of civility.

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by upside

Look guy's.. I feel you are way over the top most of us riders. We just want the fastest wheel we can buy.

Epic-o
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by Epic-o

If the second derivative of the speed is positive, the acceleration of the cyclist always increases. That's not true

I'm pretty sure that you aren't either on the same level of previous mathematicians of the country where you live in (I'm spanish)

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WMW
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by WMW

Epic-o wrote:In any case, the constant speed case is out of the question because the variable power that a cyclist generates makes the speed highly oscillant.


Please... show the magnitude of that and see if it matters.
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by Weenie


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