(Bump)

OK - So we have at least 50 people on the site who can fine tune someones position using one photo with greater accuracy than a wind tunnel, yet no one know why the science (i.e. marketing) with regard to a critical aero performance metric has done a 180 degree turn? :)

Really, no one knows. Did no one else even notice?


Paul

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2015 USAT Long Course National Champion (M50-54)

It's called marketing spin: the force data shown for crosswind conditions are those measured parallel to the direction of the wind, not parallel to the direction of travel. IOW, they indicate the degree to which you will tend to be blown sideways using various wheels, not the degree to which you will be held back. The latter is what really counts in terms of speed, whereas the former really only matters when it is variable, e.g., due to gusty winds or with wheels that tend to twist this way or that depending on small changes in wind angle (e.g., the HED3 nee Specialized Ultralight) - otherwise, you just lean over a bit and sail away down the road...

Andrew - I understand your point and that is really interesting if that is indeed the case. That basically says that in the early days of aero wheel development, everyone made a very basic science error; they assumed that higher force parallel to the wind meant more rider drag in the direction of travel. Now I hope that they at least resolved the force vectors to determine the amount of force in the direction of the rider, but maybe not. If they did resolve the force vectors to determine the amount of force in the direction of travel, then the question is still not answered.

I am also curious as to how much effect there if you neglect the amount of energy required to spin the wheel. I recently read an article from Tour magazine on the Zipp website that seemed to indicate that air drag sometimes goes up at high yaw angle while the amount of energy required by the motor to spin the wheel drops and thereby more than offsets the increase in air drag. The resulting force is that it is easier for the rider to pedal.

I am just curious where this major change in thinking occurred, and more importantly if this is just marketing or if there was a legitimate science error that has now been corrected.

Paul

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2015 USAT Long Course National Champion (M50-54)

No, nobody (to my knowledge, anyway) ever made that mistake. Instead, Nimble is choosing to present the "raw" (i.e., non-resolved) force data, since it makes their wheel look better, and other, more aerodynamic wheels, look worse. Like I said, it's marketing spin, nothing more and nothing less.


In general, translation drag accounts about three-fourths of the total drag, and rotational drag the other one-fourth. It's therefore natural that everyone focuses on translation drag, especially since it is easier to measure. When considering small differences between wheels, though, it's important to not completely lose sight of the rotational drag.


As I said, there have been no major changes in thinking (and that Nimble hype has been kicking around for at least a decade, possibly longer).

Exactly...and if you take Nimble's "data" at their word (i.e. how they present their "side on drag") why would you use their wheel instead of a 32 spoke, low section wheel in crosswind conditions? After all, it's better, right? ;-)

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http://bikeblather.blogspot.com/

Andrew missed my point. I am really not concerned how Nimble compares to other aero wheels; I am concerned how any aero wheel compares to a 32 spoke box section rim in a cross wind.

The point is that all the wheel manufactures in the 90's, including Nimble to this day, said their wheels were slower in a cross wind than a 32 spoke box rim wheel. I remember similar adds by Specialized, Spinergy, and others; the Nimble add is the only current reference I can find.

Fast forward 10 years, and many aero wheel test results still include the Specialized tri spoke. Now all claims are that the 32 spoke box rim is ALWAYS slower, regardless of wind angle. I really can't imagine that all the wheel manufactures chose to present data that made their expensive wheels look bad compared to a 32 spoke wheel ONLY to make their wheel look a little better as compared to other wheels, but maybe I am wrong here.

Summary - Old data indicated 32 spoke box section wheels were faster in a cross wind, as compared to a Specialzed tri spoke. New data indicates that 32 spoke wheels are always faster than a Specialized tri spoke.

Something has changed.... Either the data was bad then, or the data is bad now.

P.S. - I didn't mean to confuse things with the Nimble add. It is just that this is the only add still available on the internet that demonstrates the older claim that a 32 spoke box rim is FASTER in a cross wind than Nimble, Specialized, Spinergy, etc.

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2015 USAT Long Course National Champion (M50-54)

I was heavily into the aerodynamics of cycling back then, and I don't recall such a claim ever being made. I therefore think that your memory is simply playing tricks with you.

[/reply]I was heavily into the aerodynamics of cycling back then, and I don't recall such a claim ever being made. I therefore think that your memory is simply playing tricks with you.[/reply]

So I can't find the old adds by Specialized and Spinergy, but I remember they said the same thing with regard to 32 spoke box rim wheels; the aero wheels are worse in a cross wind.

I'll keep looking and see if I can find any reference to the old adds.

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2015 USAT Long Course National Champion (M50-54)

worse wrt. to handling for sure but not wrt. aero drag ... that hasn't changed.

Umm...It's either (as Dr. C said) your memory is playing tricks on you, or that the old "ad copy" was incorrect.

Multiple wind tunnel tests from a variety of sources show that the CxA (drag in the direction of travel) of a 32 spoke low profile wheel is higher than a trispoke or similar aero wheel in a crosswind condition, (or in any condition for that matter.) In fact, the aero advantage of the deep section aero wheels is GREATER in those conditions than in a 0 yaw condition.

Just because something's stated in an ad, it doesn't mean it's true. For example, Specialized is currently claiming that their Roval Star Fusee wheel is "lower drag" than a trispoke...that MAY be true in a 0 yaw condition (NO data has been presented yet to confirm this), but I highly doubt it will show lower drag in crosswind conditions, just by the nature of the rim depth and the shapes of the spokes and flanges.

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http://bikeblather.blogspot.com/

Deep section wheels (up to a point) and rear discs are better in cross winds. You get the benefit of the sail effect. 80mm and deeper rims on the front can be a handful depending on one's bike handling skills as winds get over 20 mph. In this case I personally swith to a 404 on the front. have used it in winds 20-40 mph with no problem. Have only once wished I didn't have a disc on the back. That was doing a 20K TT in a heavy thunderstorm with wind gusts over 50 mph. Of course, I wished I wasn't out on course during that storm either. Was clear but forboding at the start and the thunderstorm hit just as I made the turn around. That 10K back was some of the scariest stuff I've ever ridden in.

Ric