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Tail wind position(13 posts)

Tail wind positionTahn
Oct 25, 2001 6:39 PM
Just wonder if the wind is with you (i.e tail wind), do you ride more up right to catch it or so you still ride low and maintain your aero?
You should always feel a headwind ...Humma Hah
Oct 25, 2001 6:54 PM
Wind drag is generally the thing that limits your speed, unless you are climbing. With a tailwind, you simply go faster, and should end up feeling a headwind in most conditions. I found that to be true even in today's blustery conditions. An aero position will be of some help, even in a tailwind, except in the most extreme contitions, unless some other factor limits your speed (like a hill, or maybe safety).

That said, I got severely aero today going into the headwinds, so I could maintain 10 mph. I was out of the seat, hunched over so my back was perfectly flat, grinding away. I can't do that all day. With a tailwind, I use a more comfortable riding posture, and enjoy the ride.

With a really strong tailwind, it can be fun to play with the wind and see if it can push you effortlessly. Sit up, spread your jacket like a sail, see what it will do. But then get back to work, get the wind back in your face, and marvel at what the computer says.
World 25 mile record held by English postman...John-d
Oct 26, 2001 5:35 AM
This reminds me of the story where just after WW2 a Suffolk postman was out delivering letters on his post bike when the 1947 hurricane struck. He was spotted by an official TT time keeper who started his watch. 'Phoning a colleague who lived 25 miles away an accurate time was taken over the 25 miles. At about 10 miles a cat became attached to his chest. Unfortunately just as they passed the 25 mile line they both splattered against a barn on a sharp bend. The cat was posthumously awarded the record status for the fastest airborne 15 miles but the postman's record was dis-allowed for using a flying start.
In the Wizard of Oz...mr_spin
Oct 26, 2001 10:54 AM
When the witch is riding the bike in the tornado, should she have removed her pointy hat and spread out her cape?
Good questionDutchy
Oct 25, 2001 9:32 PM
I have been asking myself the same question lately. I feel it is still better to get on the drops
with a tail wind. As the wind pushes, sitting up would counteract any advantage as your
body will still catch more air, reducing the affect of the TW.
I also find I ride harder when on the drops.
Look at the Pros' they are always on the drops when hammering.

CHEERS.
Good questionColuber
Oct 25, 2001 10:25 PM
What's really interesting is when I ride in traffic with my french horn on my back. I have a very big hard plastic case, which catches the wind like nothing else I know. It's like riding with a sail. Makes it very very difficult, say, going along a river in light traffic in a head wind when I'm in a hurry, but there are also times when there's a tail wind or a cross wind and I can rotate myself so that I catch most of it with the back of my case rather than the side or the bell, and I can really feel the extra push straight from behind! Makes me think it would be kinda fun (if there were no traffic) to try to ride by 'tacking' across the street by using wind force alone (with my horn, of course) by going back and forth to keep the wind on the back of it *grins*
Actual tail windKerry Irons
Oct 26, 2001 4:00 AM
Remember, the actual wind you feel behind you, or in front of you, is only about half of the "posted speed." The reason for this is that wind speeds are measured roughly 20 feet above the ground, and away from any buildings, trees, or other obstructions. By definition, the wind speed right at the ground is zero, so a bike sees a zone where the speed is heading toward nothing. A reasonable estimate for the actual wind (head or tail) is half what you see on the Weather Channel. Because of this, as HH said, you should always be feeling a head wind and the more aero your position, the faster you will go. That doesn't prevent a lot of us from sitting up and relaxing a bit when we get pushed by the Giant Hand, but we would be faster if we stayed on the drops.
Missing the main point, physics....Len J
Oct 26, 2001 11:17 AM
something about vectors.

If you are being followed by a 10 mph tailwind, and you are moving thru the air at 20 mph, what are you going to feel?

Answer, like you are moving thru the air at 10 mph (in terms of air resistance.

A disproportianate amount of energy is used in cycling to move the air in front of us out of the way. This "resistance" increases exponentially as speed increases. What a tailwind does is it lowers this resistance, hence, with the same energy, you can go faster. (Yes, there is some pushing of you going on, but this is relativly small compared to the benefit of not having to push as much air out of the way) This is the same thing that happens in a paceline BTW. So, if I am correct, then an aero position would help as long as the taliwind was at a lower speed than the speed traveled.

Len
please be more clearET
Oct 26, 2001 12:08 PM
The speed travelled depends on the air resistance. So you have to be real cafrul in defining terms such as speed. Insert a tailwind and the frontal resistance increases (nonlinearly) and thus affects the speed. And the frontal area is not the same as the rear area. Etc. etc.

You have to define your terms very carefully. See also my other post.
please be more clearLen J
Oct 26, 2001 12:15 PM
"Insert a tailwind and the frontal resistance increases (nonlinearly)"

This doesn't seem right to me. If the only thing the tailwind was doing is increasing the riders speed, I would agree with this statement. However, in addition to assisting the rider, the tailwind is "pushing" (not a great word but I can't think of another, other than lowereing the pressure in front of) the wind in front of the rider out of the way, hence, I would say that a tailwind would lower the frontal resistance.

Help me understand.

Len
we punched, I mean, discussed this beforeET
Oct 26, 2001 6:17 AM
Took the gloves off, so to speak. I took the side most of you here are taking, namely that it apparently is better to tuck and stay (frontal) aero, at least in anything but a gale force wind, the reasoning being that you are not a perfect sail in the back, and will lose due to increased frontal drag. A prominent forum physics no-it-all completely disgreed, claiming you can even feel yourself going faster in a tailwind when sitting up, and that this was obvious to any superior physics being such as himself, and then called me all kinds of names and announced how stupid, naive and ignorant I was in all physics-related matters that it was beneath his dignity to talk to me. I then went to the respected

http://www.analyticcycling.com/DiffEqWindCourse_Page.html

and took the time to read through the whole thing (it takes some time, but even a lowly math major like me can do that) and then input real-life parameters for a typical rider's stats (power, speed, weight, frontal area for both aero and upright that I got from a cycling physics book). I did so for a one-way point-to-point course with a direct tailwind of various speeds, I tried it both for typical power outputs and for 0 power (coasting), I tried it for various slopes, e.g. level, and several grades downhill and uphill. In all cases for which the model does not bomb out (if you put in gale-force windspeeds, it will, as it has to numerically approximate a complicated expression which is sensitive), staying aero was better. The forum physics know-it-all said he'd check out analyticcycling.com and get back to me. It's now around a year later, and I'm still waiting.
Was he a postman? nmJohn-d
Oct 26, 2001 6:24 AM
Thanks for clearing it up...I thinkTypeOne
Oct 26, 2001 11:55 AM
I had been wondering about this recently, now that I push into a headwind on the way to work and benefit from a tailwind at the end of the day.
But I never thought of posting the question, because I found it interesting to experiment and find my answer. Hey, it gave me something to do on the same, boring commute. Now a physicist goes and spoils my fun and answers the question!
Btw, I thought going aero was better.