Question about position
#3
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Figured it may come to that.
I was watching a circuit race on Sat and was looking at the positions of the guys in the open race. I noticed that the guys who seemed to size down a lot for a large saddle to drop didn't seem as stretched out as the guys on larger frames who seemed to be able to get into a flat back position. They seemed to get the front of the body lower but with a curved back and straight arms while the guys on larger frames seemed higher but had a nice looking flat back position with elbows bent a lot more in the drops.
I was watching a circuit race on Sat and was looking at the positions of the guys in the open race. I noticed that the guys who seemed to size down a lot for a large saddle to drop didn't seem as stretched out as the guys on larger frames who seemed to be able to get into a flat back position. They seemed to get the front of the body lower but with a curved back and straight arms while the guys on larger frames seemed higher but had a nice looking flat back position with elbows bent a lot more in the drops.
#4
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They're obviously running too short of a stem
https://www.bikeforums.net/showthread...he-pro-peloton
https://www.bikeforums.net/showthread...he-pro-peloton
#6
Both?
#7
Perceptual Dullard
#8
fuggitivo solitario
btw, can you tear me apart on this position?
11-12cm of seat to bar drop, maybe another 1-2 cm of stem to hood drop.
above is my preferred position, one in which i can sustain for hours at a time
i have no idea what i look like in the IAB
#9
Perceptual Dullard
btw, can you tear me apart on this position?
#10
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At zero yaw. And I have yet to do a race or TT at 0 yaw. Not that field testing doesn't have it's merit though, I have some slated as soon as the wind dies down around here. And yes I know that the "Chung on a Stick" will someday be released.
#12
Perceptual Dullard
#13
Resident Alien
Ba ha ha ha.
After looking at less tests than Nate but more than a lot of folks, there's no substitute for the tunnel if you're looking for small differentials or data for different yaw angles, and everybody is different so what works for one person is what works for one person.
You can do a lot with field testing though, at least get in the ballpark at the smaller yaw angles. I can PE position to some extent at this point, especially on the road bike.
#14
fuggitivo solitario
i posted this in the stickied TT thread but received no answers.
How much does Cobb charge for fitting and does that include tunnel time? Feel free to PM me if such information is confidential.
How much does Cobb charge for fitting and does that include tunnel time? Feel free to PM me if such information is confidential.
#15
Perceptual Dullard
and everybody is different so what works for one person is what works for one person.
#16
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How fast do think people ride TT's? Let's take look at this. We'll use a rider speed of 25 mph, which is often an amateur racer's goal speed for a 40 K. A 5 mph cross wind will create a 11 -12 degree angle of wind on the rider. Now, let's look at a faster rider. Let's use a speed of 29 mph, a speed some fast guys can do like Racer Ex. The same 5 mph crosswind will create a wind angle of 10 degrees. So how fast do you have to go to make a 5 mph cross wind "0"? Well, lets just say that even at the speeds the guys in the TTT in the Tour de France went yesterday, it'd still be 7 degrees.
Now, let's look at a situation that is quite common. 0 yaw can lead you astray. What is fast at 0, is not necessarily fast at, 7, 10, 15, 20 etc. Here is some actual wind tunnel data of someone testing helmets. If you did some field testing, and did it well enough to call it " as good as tunnel data" you would look at the green helmet and say it was easily the fastest.
Then, you go out to a TT course that is out and back, and runs East/West. There is a north wind of 7 mph, which is very common at this course. For simplicity sake I will round the drag and math to make even numbers, but you just gave up 10 watts. I think Field testing has it's place, but I don't think it's correct to say that it can equal wind tunnel data.
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Missed this, sorry. I'll ask John what he's charging for a fitting these days.
#18
Perceptual Dullard
How fast do think people ride TT's? Let's take look at this. We'll use a rider speed of 25 mph, which is often an amateur racer's goal speed for a 40 K. A 5 mph cross wind will create a 11 -12 degree angle of wind on the rider. Now, let's look at a faster rider. Let's use a speed of 29 mph, a speed some fast guys can do like Racer Ex. The same 5 mph crosswind will create a wind angle of 10 degrees. So how fast do you have to go to make a 5 mph cross wind "0"?
I think Field testing has it's place, but I don't think it's correct to say that it can equal wind tunnel data.
1) only an on-bike wind sensor will tell you the "true" (i.e., weighted) exposure to yaw.
2) I've measured the sd of a carefully done field test estimate of CxA at .0006 m^2 for a CV of 0.3%. Compare that with the CV of a wind tunnel estimate.
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Sorry, didn't catch that you were kidding.
1) Vaporware
2) Why worry about an estimate of CxA? Drag, in grams, no estimation.
2) Why worry about an estimate of CxA? Drag, in grams, no estimation.
#20
Batüwü Creakcreak
1) Ibike?
#21
Perceptual Dullard
2) CxA is independent of v and rho. [Edit:] https://forum.slowtwitch.com/gforum.c...417364#3417364
iBike doesn't measure yaw.
Last edited by RChung; 07-04-11 at 01:51 PM.
#22
Resident Alien
And there's still a McGyver creativity factor if you go off piste and start fabbing up your own bits. Trust me, there's nothing quite spending hours cutting, grinding, and drilling only to find you went completely backwards on that base bar.
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1) Well, in a commercial sense, yes, but I'm not really talking about any particular commercial product. There are several working sensors out there that I know of and it's possible (though tedious) to make one yourself. The sensors I know of will, of course, differ in their sensitivity depending on who made them and the design decisions that were made. And, in a deeper sense, as far as wind tunnels go they may as well be vaporware to me and to most of us -- the nearest wind tunnel is far away and way out of my price range.
2) CxA is independent of v and rho. [Edit:] https://forum.slowtwitch.com/gforum.c...417364#3417364
#24
Perceptual Dullard
Not directed at you specifically, but there may be a bit of false economy in this thinking for a fair number of people, both in time and in dollars. It's pretty easy to drop $1000-$1500 in equipment upgrades or hours field testing and come away with a lot less than dropping $1500 and a couple of days to go to a tunnel. Granted it will be out of some people's time/dollar budget, and gains will vary according to who's running the show, but my experience has been on a $/w basis, it's a very competitive investment.
A trip to the tunnel costs a lot less that some fancy wheels. Of course, if you add cost to the equation, things get more speculative. But that's not the discussion. The reality is, most people are not going to build this sensor. Plus, how would you validate the results of your sensor's reported wind angles? A trip to the tunnel?
#25
Resident Alien
I'm sure we could develop field test equipment that is as precise as a wind tunnel, given that most wind tunnel equipment was generated off of field technologies. And I know there are days when field testing yields very tight results. The problem with field testing (especially beyond zero yaw) is consistent external conditions. And by time you've invested the time and money into the equipment you'd need to offset this problem, you could likely go to the tunnel a bunch.
But more than external conditions is rider input. Even in the tunnel with the most disciplined rider, there's noise. You get a swing and give it the old WTF? Look at the camera overlays and you see what happened. Moved the hands/fingers/head a little. I'm doubtful a person pedaling out on the road or even coasting maintains near the position consistency they would in the tunnel, and the logistics to even verify this are another matter.
And like proximity to a tunnel, proximity to a location that affords favorable conditions is a bug in the rug. I had to wait over a month once in Texas for a day where the wind wasn't blowing and the temps were stable.
I like field testing BTW. It's a heck of a lot better than nothing.