But Astana went with the Lightweight.

But they got banned from the TdF.

Wow get back form some racing to find a lot of good responses.

marc66thomas - I should have mentioned that theses wheels would server all purposes other than TT wheels. They will be crit, RR, and training wheels, as I don't really have the loot to upgrade to SRM or multiple Powertaps. Therefore, I wanted some all rounders. The 58 mm Zipp (williams), AC 58 mm (team sponsor), 50 mm Neuvations, etc, are all at the top of my list based on the fact that they seem to have the most aero benefit while remaining fairly light. I'm also going with tubular, as I'm finally convinced at how much difference good tires can make as well.

cdr - As usual, a great story :)

Just to clarify, in a slightly off-topic post...

Many of our tests are conducted on bikes, with riders (most of which don't get publicized quite as heavily as our last test with CSC, if at all). These results are typically not released as there is considerable variation in results due to different frame and fork configurations, rider positions, etc.

The fun begins when evaluating the accuracy of our mathematical models developed for comparing wheel-only savings to that in a typical bike. We've refined them to the point where they are typically accurate within about 1-2 percent, and actually on the conservative side. As an example, our calculations were suggesting a savings of 58-60 seconds per hour for Fabian Cancellara with a switch from the Ambrosio wheels typically used in the classics to a pair of 404s. When we got into the tunnel with Fabian last year, it actually worked out to a 63 second savings (so in this case we were actually 5-8.6% conservative). This is based on the bi-modal distribution of effective angles we have arrived at via data collection and examination of NWS data.

Yup, rider position/pedaling is difficult to duplicate test-to-test; and errors in rider position would be of the same magnitude or higher than the difference in wheel-to-wheel changes.

1. Asgelle - although I believe you, I have not seen MIT agreeing that 5 to 15 degrees is appropriate. Even granting that (I believe 5 degrees is reasonable), I have not seen MIT concurring that at those angles, helmets don't matter as much as wheels.

2. The Michigan state TT championship starts about two miles or so from my house. On the ride there, I pass by a college weather station. The anemometer, located fifty feet in the air and hundreds of feet from treelines, etcetera was dead still, just like it was for the other TT's held on the same course.

Has anyone here ever been out in "20-40 MPH" headwind? If you can't ride at 30 MPH normally, how can you ride against it at all?

One problem is that the measured windspeed has little to do with the actual windspeed; because weather stations do not measure wind three feet off of the ground, near the trees that I ride by on my trip through the local parks.

Moreover, averages are even worse - because much published data is based on average wind power; which, being a cube function of windspeed, overweights higher velocity wind.

Estimating an average TT windspeed based on published data is warrantless and without merit.

Taking data? Sure. I haven't ever seen the data, so I don't know. I *do* know that my TT's are generally held in the later morning/early afternoon of summer days - when the windspeed is almost always below the "average" for the location.

When pulling a 25 MPH average, the wind speed AT THE GROUND needs to be 10 MPH for the average wind angle to be 15 degrees. Using Zipp's 30 MPH testing criteria, the average windspeed needs to be 12 MPH.

What 'weather-station-measured' speed does this work out to be?

Well, this reference says that the ratio between near-ground wind speed and measured wind speed is between 0.2 for urban areas, 0.3 for (more or less) vacant lots in urban areas, and 0.8 for farmland type spaces. Should we use 0.5 for our purposes? Riding 50 feet from the treeline, I think it's reasonable. So, for these assumptions, in order to have an 'average' 15 degree headwind, at the 30 MPH mark, the measured windspeed would need to be about 24 MPH.

That's one hell of a wind for mid-summer afternoons. And I live in the midwest.

Of course, that doesn't mean Zipp isn't a great wheel. I have some 404's, and would've bought some 303's this past week if a teammate hadn't wanted/needed them more. But 15 degrees? I've never raced in those conditions.

http://hedcycling.com/technical/yaw-calculator-app.php

And I don't know the specific wind speed, but I was out last year pushing 350-360w steady and going 13 mph. It was the worst day of my life at that point. I swear the wind was 80mph head on.

I know of one person who does has used an anemometer placed 3 ft. above the ground to take direct wind measurements during his testing. He believes 0 yaw is not the best choice but somewhere between 5 and 15 degrees is a better angle.

incorrect.

Yup, which is why I welcome 'measured' (in this case, data measured specifically for analysis in cycling) data. I'm sure that 0 degrees is not the best single number; and I'm sure a weighted number would do better. Of course at altitude in the western states, the numbers would probably be higher. At low altitudes/in the east, the yaw numbers would probably be lower. For my most important events those numbers have somewhat coincidentally been 0. If I had to guess what the angle would be for this year, I would guess 5 degrees (about a 7 MPH weather-station measured wind). That's still a pretty brisk breeze for mid-summer mid-afternoons.


The difference between 202's and 808's at zero degrees? ~5 watts. At five degrees? ~7 watts.

Just a few thoughts/posts from a few well known sources;

From Coggan

Quote:

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As I mentioned, it's rare that we have absolutely still air through which to pedal, even on an indoor track. The consequence is that there is practically always some crosswind, such that yaw angles of approx. 10-20 deg are far more common than yaw angles <10 deg or >20 deg. Indeed, even in absolutely still air on an indoor track, the yaw angle approaches 10 deg in the turns, due to the fact that the cyclist is constantly changing directions.

---

And John Cobb

Quote:

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This has been an interesting thread and I wanted to share a couple of my observations on this topic. I think that testing at a single yaw point like 6-7degrees might be a very good idea. Of the "bicycle tunnels", the A&M tunnel is the one that can rotate or yaw very quickly, it can sweep from 0 - 90 degrees in under 1 minute while giving data points. I test there because it is 2 hours from my house so it's convenient and I have become accustomed to doing multiple yaw sweeps for each run. I did see early on that the results that were best at "0" were not always the best for an average yaw run but it also depends on what the rider's goal is as to the importance. As an example, for track racers I often test at every degree from 0-5, for triatheletes/TT racers, I test at 0-2.5-5-7.5-10-12.5-15-20. I would encourage any of you that go to tunnels to test, to do the test with standard wheels and not a disc or very deep rims. The air flow does not break off these race wheels consistantly and getting small data changes is a lot more difficult. I would also encourage you to do several repeats of various runs to verify the changes, all tunnels tend to "creep" and we are dealing with such small drag numbers it is easy to go down the wrong path without double checking the data. I established the standard testing of Drag @30mph, this was done to give high enough force numbers so that they would be repeatable. I would like to get some of you racers opinion as to a good "average" yaw, I will invest the time[and money] to go gather some data at that yaw point and maybe we could establish a new single point yaw for everybody to use. I would still encourage you to test at multiple yaws when possible but a consistant 5-6-7or 8 degree call out might be very helpful. It would be very easy for any tunnel to test at a single yaw point and as more people learn about this type of testing, more speed will be found for everybody.

---

interesting. it seems as though all of us are in favor of somehow collapsing the data into a more accessible single number, and the distress is over the weight of measurements at different yaw angles. even cobb doesn't seem to know which angles are the most common for typical tts. that does not bode well for a small brain like me.

Yeah, he mentions that he tests at many different angles. Even HED data shows a 90mm rear is very close to a disc up until 15 degrees. They said that some people are more aero until 15 with a 90mm or H3D, while some are still faster with a disc. At 15 degrees the disc has 1/4 the drag of a Stinger 90, but at 0 it's less than 5 grams. I took a chance and went with the Stinger 90 rear because they say a disc seems to matter less when you have a seat tube cutout and the new disc "redesign" was going to leave me without a rear race wheel at one of my big races this year. Plus I can now run a rear 90 in Lynchburg or similar races where it's windy but flat.

Bull.

These numbers might be reasonable. I like the 5 degree. 15 is out to lunch; much more rare in my experience than 0 degrees. Of course, at 5 degrees wheels only make 7 watts of difference, and at 15, they make (guestimating without looking at the chart again) 20. So we only hear about 15 degrees.

hehe, I love that sound too :D

Hey, he's on the site, lure the good Doc out for discussion.

Who, moi? :D

FWIW, the velodrome yaw data in question were collected by Chet Kyle et al. as part of Project 96, and can be found in Burke's "Cycling Science" (don't recall what page/figure number, though).

Well, I was hoping for Dr. Day or Paulo, but I guess you'll do since you're here and all. :D