When riding with your local group, are you guys actually pushing the guy thats pulling the group??? What I mean is this, in nascar everyone rides around in a group, but when it comes time to pass someone, that person ( my boy Dale JR ) looks for someone to actually follow and push him past the lead car which sometimes the whole pack does and thus dropping the lead car by at least 10 positions, does this rule apply to cycling as well??? I know its aerodynamics and the nascar guys are going waaaaaay faster but sometimes when im pulling, im at speeds that i normally dont ride at??? Is this fact or fiction???
From what I’ve read, the lead rider does gain some, much lesser, aerodynamic advantage by having other riders draft behind. As I understand it, it’s not literally “pushing” the lead rider. I think it has to do with the fact that the drafters reduce the turbulence behind the lead rider, but I’m sure many on this board can provide a better and more accurate explanation than I.
I think the best that can be said is that to this point there has been no empirical data or theoretical explanation to support the hypothesis that following riders reduce drag on a lead rider. Cars move much faster and have much greater frontal area than bicycles.
I have read somewhere, more than once, that there was scientific evidence that the lead rider in a group did benefit some very small amount from having a trailing rider/riders draft him. This small amount was on the order of 1-3%, an amount so small that it would be virtually impossible to recognize the difference.
This should not be mis-understood to mean that the rider in the lead is not doing 30% or more of the work that drafting riders are. Or that the rider on the front won’t tire faster than the following riders.
“I have read somewhere, more than once, that there was scientific evidence that the lead rider in a group did benefit some very small amount from having a trailing rider/riders draft him.”
People keep repeating this usually saying as you did that they read it “somewhere”, but no one has been able to supply a citation (I know about Kyle’s statement on isidetri.com, http://www.insidetri.com/train/bike/articles/1311.0.html but he doesn’t provide any data to support his assertion, the reference there only addresses the following riders). I think this is becoming another urban myth.
In reply to: "I had always heard exactly the opposite … that having a rider sitting on your wheel will drag on you a bit. I have nothing to site to support that. It may be a psychological thing. But if having a rider on your wheel pushes you, why would teams in bike races send riders to “mark” any move made by a key rider from an opposing team? "
When a team sends a rider to go suck on the wheel of another team, that rider sits on the wheel and puts no effort into pedaling with the lead rider thereby constantly pulling on the rear wheel of the lead rider and forcing him to pull both cyclists. If the two were to work together and the rear rider puts effort into pedaling, stays with the lead rider and doesnt sit back, then the two will have an advantage because the lead rider will benefit from the draft. If the rider in the back just “sits in” with no effort he makes it difficult for the guy up front.
Think about the paceline in the team time trial. They all recieve an advantage from the group effort.
The following rider can either “pull” the lead rider or “push” him, depending on the distance they’re at, but we’re talking about forces with a very small magnitude, certainly forces that you can’t feel.
i raced on the raod for a few season in master A. when you’re on the front it’s up to you how hard you go. if you sit up, the group moves around you. even in bigger group rides i found this can happen. now can someone push you to the front? i’d say yes. if you pull to the outside, lets say just to get out of the crowd, they can react and get behind you. then all of a sudden your pulling 50 riders wondering how it happened. Then in another 20 seconds someone jumped and you’re hanging on for dear life at the back.
road racing is an awesome sport. every triathlete should go out and do a few raod races.
If you have two riders, one right behind the other, and I mean as close as possible w/o touching, you could consider the two bikes and riders to be in fact one long vehicle. When you push thru the air on your bike, the air you have pushed thru will “curl” around behind you into vortices. Those vertices of air that are swirling behind you will in fact push you to some extent (you’ve also changed the air density behind you, but let’s try and keep it simple here). That effect is pretty neglible in most cases. If you have a single rider, with vehicle length l, there will be some fancy formula (which I may have to go look up again now, damn that curiosity!) to calculate both the drag (force pushing back on the rider) and any forces pushing the rider forward (like these trailing vortices), which will have some relationship to l. If you have two riders comprising one vehicle, the length l is nearly doubled. If I recall correctly, the drag (pushing) force has less of a relationship to l than the training (pulling) forces do - drag is more related to frontal surface area. But those trailing forces will increase in magnitude, again probably in a pretty neglible way.
Once you get a huge pack of riders, the frontal surface area is huge, so the impact to the lead rider has got to be almost completely wiped out.
I’m going to go dig up my fluid dynamics stuff and check.
Close explanation, but it would be better to idealize the rider’s body as a cylinder for drag approximations since it accounts for a large portion of the total drag. If you were to assume the flow around the rider is turbulent, the reverse flow caused by the vortices would be cancelled by the higher skin friction drag. Now the effect of a second rider depends a lot on how close their bodies are rather than how closely their wheels are spaced. In a relative headwind with the second rider directly behind the first, there is a distance of about 2D, with D being the wetted diameter of the cyclist’s body. This distance is just on the edge of interfering with those vortices enough that you could increase the pressure in the region behind the first cyclist such that there could be a reduction in pressure drag pulling on the first cyclist.
Now, if you had two cyclists in an echelon with a relative head/crosswind, the distance between the two could be reduced to less than D, which would give a lowered pressure differential across the body of the first cyclist. But this would only decrease the magnitude of the drag at the relative wind angle such that magnitude of drag in the direction of motion would not decrease noticeably.
“Sitting” on a rider to make him do more work is really just a psychological effect.
He seems to support the contention that any reduction in drag would be suffiently minute that it would be unnoticeable by the rider. I think that is what I indicated, as well. So I think we are in agreement here.
Yes, there can be a reduction is drag on the first rider if there is a trailing/drafting rider. No, it is not great enough to be noticeable.
I guess we’re down to the level of semantics now. I, too, agree there is a reduction in drag and estimate it on the order of 0.1% or less. So for the purpose of argument, if we all agree that this is the magnitude of the effect, how do we answer the original question; is the leading rider pushed along by the trailing rider? I think the best answer is that he is not. If others want to answer that there is an effect but it’s too small to detect, I have no problem with that.
I used the link and went to the article. I have to say, I liked Dr. Chester Kyle’s statement regarding his wind tunnel testing. But I guess you can tell why. At least I have learned company when talking out my a** with unsupported contentions.
“Answer from aerodynamics professor and Project 96 and 1984 U.S. Olympic Team bike designer, Dr. Chester Kyle:
We measured this in the General Motors Wind Tunnel in 1996, and on the track using the SRM crank dynamometers. The lead rider in a 4-man pace line uses about 2 to 3 percent less energy than they would if riding solo.”
I have a problem with Kyle’s reply though. If you read the rest of his answer, he cites a paper as the source for his answer; but if you read the paper, it reports the data on drag reduction for the following riders, but does not have data on drag reduction for the lead rider (though the answer you quote implies the paper does). I’ve also been unable to find any other publication where he reports the data on the lead rider. So I have to ask, 1) why isn’t the data on the lead rider published, and 2) why did he phrase his answer to give the impression that it was.