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Drafting in a paceline: Aero or Psychological?(7 posts)

Drafting in a paceline: Aero or Psychological?rainy day rider
Jun 19, 2001 8:45 AM
So I was riding to work with my brother this morning, and we were taking turns pulling one another. You can certainly tell in the back that you don't have as much drag, due to the shielding. I also felt that I was riding faster when I was in the front.

I know that there's a benefit to drafting for both bodies in a paceline, I learned that in one of my fluids courses. I'm wondering how much of this benefit is real, and how much is psychological. I really felt like we were cranking today, it felt good.

Also, you riders in long pacelines, can you feel the difference between 3 riders in a row and 5? 10?

-rdr
re: Drafting in a paceline: Aero or Psychological?Len J
Jun 19, 2001 9:50 AM
Based on studies second bike within 6 inches = 43% less effort.
W/in 1 ft 30% less effort. Has to do with air resistance. When riding alone, a very large part of the effort is Moving air out of the way.
Very large indeed...Lazy
Jun 19, 2001 9:53 AM
IIRC, I read that as much as 82% of effort is used to overcome air resistance.
figuresPingPong
Jun 19, 2001 10:30 AM
I the proportion of effort required to overcome air resistance increases with speed. So at 15 mph you will not get anything like the drafting benefit that you will get at 25 mph. This is one reason you might want to attack on a climb.

Riding at the front of a group does feel faster, it's as if you have lost some of your drag to the chain behind you. However it's such a motivator having several riders behind you that I can't be sure how much of this is mental.

If you would like figures here's one : 19 %
And another : 18 %
Thanks, all, and drag relationsrainy day rider
Jun 19, 2001 11:47 AM
While it seems that no one can agree on exact numbers (and that's fine by me, I'll take the 82% mentioned), it's a good point about the impact of velocity. The drag increases with the square of velocity, so the effect of the paceline is reduced on a hill (good point about attacking then, PingPong).

Drag = (1/2)*(fluid density)*(Drag Coefficient)*Area*Velocity^2
The drag coefficient is based on geometry, and I don't know what it would be for a cyclist. Modern cars range from Cd = 0.2 and up, and a VW microbus or other flat fronted trucks are about Cd = 1.0

A body passing through a fluid generates a low-pressure area behind it, and this low-pressure area tries to 'suck' you back. A drafting rider in this low-pressure area behind you carries this load for you, so all you have to deal with is frontal drag.

So, in a tight paceline, the front rider has to deal with frontal drag only, and the rearmost rider has to deal with low-pressure wake but no frontal drag. The in between riders are along for the ride, except for maybe a little shear.

I still can't quantify the psyche stuff. It would make for an interesting experiment.

Hmm, I think I answered my own question!

-r(not today)dr
what about on climbs?DAS
Jun 19, 2001 5:29 PM
What about on climbs? In bike races it seems that teams will 'work together' on climbs, but aren't they going too slow to draft off eachother? Are they just drafting off each other a very little bit, and it adds up over time?

also, how can a rider go after an attack and 'pull him back' to the group? Does he ride in front of him and then slow down, blocking him?

I've got questions, but no figures.
Drafting still appliesmr_spin
Jun 19, 2001 6:27 PM
Yes, drafting isn't as useful as often in the mountains. But trust me, it helps, because you can get some strong winds in the high mountains. Mountains tend to make their own weather. Climbing a long, steep mountain pass into a headwind is true suffering.

Also, unless there is a mountain top finish, you're going to come down at some point, and you'll want some teammates with you to pull you across the valley to the next mountain. Mountain valleys can be wind tunnels sometimes.

But there is no way anyone can 'pull' you up to the leader. Everyone has to get to the top on their own. That's just an expression used to describe the mainly psychological effect of sitting on someones wheel. A classic example is if your rival attacks on a climb and you have a team mate with you, your mate should immediately chase the guy down and sit on his wheel. Now your rival has to worry about dragging your team mate to the finish with him, with theoretically fresher legs. Unless he is feeling extremely confident, he won't do that. His attacked is "neutralized." Meantime, you've accelerated at a more comfortable pace and caught up. This will typically happen over and over again until someone gets away. By that point, your teammate will probably be shelled out the back. Hopefully, your teammate will be attacking the group as well. The point is to eliminate the weak, and your mate is supposed to kill himself helping to do it.

Blocking can also be done, but I don't think it happens much at the pro level. Do that and you'll get some payback at some point! But if you notice that your rival has allowed himself to be boxed in by other riders or the crowd or some other obstacle, attack immediately. There's nothing unethical about that.