Turbulence - Is it harder to ride at the back than in the middle of a group?

[IBarrett]

Evening all,

its well known if you're riding in a group it's harder to lead because of the air resistance and that you punch a hole in the air for the guy(s) following
I got thinking last night when at the tail end of our group and wondered if the same effect of turbulence and drag which applies to the back of a racing car also applies to the tail end Charlie in a group of cyclists.
So in effect it's harder to ride at the back than it is in the middle of a group.

Has this been discussed here or documented anywhere?

 

[Shaun]

I can't say I've experienced or noticed this before (and I've done my fair share of clinging on to the back of a group ) but then I've never really been a fast rider and I expect any impact from this would increase relative to the speed of the pack; any of you racers ever felt that being the back marker is not as free a ride as you might expect?

 

[Yellow Saddle]

Your observation is correct. There are two reasons why it is harder at the back than third or fourth from the front. The first is aerodynamics. The benefit reduces slightly as you are further back in the group, with the best position being about third or fourth from the front.
The second reason is the elastic band phenomena. This you may have noticed in stop-start traffic where a group of cars are stopped and then the light turns green and they go again. The second car starts moving when, say, the first car is already 5m ahead. The third car starts when the second car is 8 meters ahead and the fourth car starts off when the third car is 15 meters away. To then maintain an equal following distance of 5m, the last car has to make up 10 meters whereas the third car only 5m. The longer the queue, the worse the elastic band.
In a peloton the same happens. The leader adjusts speed for whatever reason and the gap ripples backwards with ever-increasing gaps between cyclists. By the time the last rider can react, the gap is huge and he has to jump. Doing this repeatedly very quickly exhausts your energy stores. Usually this "jump" is fuelled from ATP, not aerobic fuel sources and there is a very limited quantity of that available to the rider. (We improve ATP usage with interval training).
It takes a very skilled bunch of riders to minimise the stress on the rear person. Even though the person at the rear won't remain there all the time, over the course of 40kms you may end up there 100 times and 100 jumps takes it's toll.
The elastic band could be used tactically as well. If there is a breakaway of say 5 people but one of the 5 is from an alien team and thus the enemy, you wear him down. Each time he has just done his turn at the front and drifts back, you wait until he has just tucked in behind the last rider and then you cause a little jump. Not a massive one, just enough to make him think he can now sit and rest but alas, not. Do this five times and he falls out the back of the peloton.
Another way to wear down an unwanted wheelsucker is to wait for a headwind slightly from the right. You then maneuvre your peloton so that the last person can't tuck in because there is no road on the left, just gutter. He then hangs on but with half his body in the wind. As soon as a friendly rider goes to the back, you move the peloton over and give him plenty of space.

 

[400bhp]

I've found out to my cost, when racing this year, that at the back is not a good place to be. Trouble is, moving up the pack is a lot easier said than done.

The elastic band phenomena, like @Yellow Saddle pointed out, being in full effect and exacerbated in crits with tight bends. Crits are not my strong point, saying that, I'm not sure what is.

 

[andrew_s]

The elastic band effect is really a spring effect - it works in braking too.
The front person slows for a sharp corner, the second person brakes a fraction later, and has to brake harder not to run into the back of the rider in front, and the next person in line even harder. By the time you are 10 riders back, you will be nearly stopping, and having to sprint to get back on the wheels.

Another problems with being at the back is the indication of potholes. The front rider indicates a hole, but it takes the second rider half a second to react and indicate in turn, and if he's gone further in that half second than the gap between riders, will be closer to the hole when indicating than the first rider was. Several riders back, there's no time to indicate or dodge, just grab the bars tight, unweight the saddle, and hope.
Shouting rather than indicating communicates further back, provided that everyone echoes the call rather than assuming that because they can hear the call, the next rider back can too.

 

[T.M.H.N.E.T]

Your observation is correct. There are two reasons why it is harder at the back than third or fourth from the front. The first is aerodynamics. The benefit reduces slightly as you are further back in the group, with the best position being about third or fourth from the front.
The second reason is the elastic band phenomena. This you may have noticed in stop-start traffic where a group of cars are stopped and then the light turns green and they go again. The second car starts moving when, say, the first car is already 5m ahead. The third car starts when the second car is 8 meters ahead and the fourth car starts off when the third car is 15 meters away. To then maintain an equal following distance of 5m, the last car has to make up 10 meters whereas the third car only 5m. The longer the queue, the worse the elastic band.
In a peloton the same happens. The leader adjusts speed for whatever reason and the gap ripples backwards with ever-increasing gaps between cyclists. By the time the last rider can react, the gap is huge and he has to jump. Doing this repeatedly very quickly exhausts your energy stores. Usually this "jump" is fuelled from ATP, not aerobic fuel sources and there is a very limited quantity of that available to the rider. (We improve ATP usage with interval training).
It takes a very skilled bunch of riders to minimise the stress on the rear person. Even though the person at the rear won't remain there all the time, over the course of 40kms you may end up there 100 times and 100 jumps takes it's toll.
The elastic band could be used tactically as well. If there is a breakaway of say 5 people but one of the 5 is from an alien team and thus the enemy, you wear him down. Each time he has just done his turn at the front and drifts back, you wait until he has just tucked in behind the last rider and then you cause a little jump. Not a massive one, just enough to make him think he can now sit and rest but alas, not. Do this five times and he falls out the back of the peloton.
Another way to wear down an unwanted wheelsucker is to wait for a headwind slightly from the right. You then maneuvre your peloton so that the last person can't tuck in because there is no road on the left, just gutter. He then hangs on but with half his body in the wind. As soon as a friendly rider goes to the back, you move the peloton over and give him plenty of space.

This post is solid gold

 

[andrew_s]

wondered if the same effect of turbulence and drag which applies to the back of a racing car also applies to the tail end Charlie in a group of cyclists?

Yes.
If you have someone close behind, you experience a bit less drag than if you don't. That's true even if there are only two of you and you are the front rider. In a larger group, the tail end Charlies don't get this benefit.
In a really big group (TDF peloton), the riders along the side edges will also see more drag than those in the middle.

The "elastic band effect" is more commonly referred to as the "concertina effect"

 

[S-Express]

All I can say is that over hundreds of road races and crits, I've never felt any disadvantage or any difference in being at the back of a bunch - from an aerodynamic perspective. As pointed out earlier, there are many other 'tactical' reasons why being at the back is not necessarily an ideal place to be - but aerodynamics (or specifically, having to make a higher effort at the back than being elsewhere in the bunch) does not appear to be one of them.

Interesting view on the aerodynamics of bunch racing here: http://cyclingskills.blogspot.co.uk/2008/07/most-efficient-positions-in-pack.html - no idea whether it's valid or not, but it seems to suggest that being at the back is not as bad as some are implying, which certainly bears out my own experience. Worst places to be, according to the chart here, are the first few rows, which is a shame, because from a tactical perspective, being in the first 10 or so is definitely the best place to be. It does kind of support the notion that the fittest riders tend to be at the front anyway, for whatever reason.

 

[S-Express]

If there is a breakaway of say 5 people but one of the 5 is from an alien team and thus the enemy, you wear him down. Each time he has just done his turn at the front and drifts back, you wait until he has just tucked in behind the last rider and then you cause a little jump.

Have you ever done this? If I was the 'alien' rider in your break, I wouldn't be doing any turns on the front. I'd be sitting in and saving energy, because I'd be well aware I was going to get mugged at some point further down the road.

 

[cyberknight]

The elastic band effect is really a spring effect - it works in braking too.
The front person slows for a sharp corner, the second person brakes a fraction later, and has to brake harder not to run into the back of the rider in front, and the next person in line even harder. By the time you are 10 riders back, you will be nearly stopping, and having to sprint to get back on the wheels.

Another problems with being at the back is the indication of potholes. The front rider indicates a hole, but it takes the second rider half a second to react and indicate in turn, and if he's gone further in that half second than the gap between riders, will be closer to the hole when indicating than the first rider was. Several riders back, there's no time to indicate or dodge, just grab the bars tight, unweight the saddle, and hope.
Shouting rather than indicating communicates further back, provided that everyone echoes the call rather than assuming that because they can hear the call, the next rider back can too.

+1
In a club ride the front swerved and braked to avoid road kill and as i was near the back i only had time to grab my brakes and got rear ended by the guy behind me .

 

[Yellow Saddle]

Have you ever done this? If I was the 'alien' rider in your break, I wouldn't be doing any turns on the front. I'd be sitting in and saving energy, because I'd be well aware I was going to get mugged at some point further down the road.

Yup. But it depends on the tactic of the moment. Have a look at the races in TV. During the breakaway the alien rider co-operates and often even pulls. He knows he's gonna be mugged but he wants to stay in the little bunch and not get dropped in no mans land and swallowed by the peloton behind.
With a side wind it is relatively easy to wear an alien rider down if he never goes to the front. If there were four of us and you in the little bunch and you don't help, I'd jump you on every corner and pull your elastic until it twangs and then ride you in the gutter or over the white line if there is a commissar watching.

 

[Yellow Saddle]

All I can say is that over hundreds of road races and crits, I've never felt any disadvantage or any difference in being at the back of a bunch - from an aerodynamic perspective. As pointed out earlier, there are many other 'tactical' reasons why being at the back is not necessarily an ideal place to be - but aerodynamics (or specifically, having to make a higher effort at the back than being elsewhere in the bunch) does not appear to be one of them.

Interesting view on the aerodynamics of bunch racing here: http://cyclingskills.blogspot.co.uk/2008/07/most-efficient-positions-in-pack.html - no idea whether it's valid or not, but it seems to suggest that being at the back is not as bad as some are implying, which certainly bears out my own experience. Worst places to be, according to the chart here, are the first few rows, which is a shame, because from a tactical perspective, being in the first 10 or so is definitely the best place to be. It does kind of support the notion that the fittest riders tend to be at the front anyway, for whatever reason.

The diagram in that link shows the most ideal peloton possible. Of course the blue chaps in the middle have it the easiest. It is a wonderful place to be. The riding is effortless and quiet with far less wind noise than any other position. It is also the hardest place to remain. The pack dynamic makes you have to constantly fight to remain there and if everyone co-operates, you're only there for a short while in anyway, as you are constantly moving forward as the tractor pulls over and let someone else take a turn

Such a peloton can usually be found in the forerunners of today's mass-start races, each category will be lead by such a pack for a while. For most people though it is a matter of a small bunch, probably single file and not all that trained and skilled to do what they're supposed to do. If you want to be mercenary, the best place, aerodynamically and tactically is third or forth. The airflow diagram for such a bunch doesn't look like your air-foil in the link. There's a sweet-spot about one third down in the line. Maybe you can't feel it, nirvana is not always all that obvious.

 

[S-Express]

If there were four of us and you in the little bunch and you don't help, I'd jump you on every corner and pull your elastic until it twangs

But in doing that you would be wearing yourself down too - ergo no advantage ultimately - all he has to do is sit on a wheel and go with the accelerations, as the 'elastic theory' has no real impact on such a small group. It also depends on the relative fitness of whoever it is you are trying to drop. Pointless trying to do that with a strong rider - simply trying to ride him off your wheel is probably the worst thing to try.

and then ride you in the gutter or over the white line if there is a commissar watching.

Both of those things constitute dangerous riding though and would likely result in you getting a warning, or being pulled out if the comm saw it. Not worth the risk. Deliberately putting someone over a white line could have a lot of unintended consequences.

 

[Yellow Saddle]

Both of those things constitute dangerous riding though and would likely result in you getting a warning, or being pulled out if the comm saw it. Not worth the risk. Deliberately putting someone over a white line could have a lot of unintended consequences.

Are you assuming contact? I am talking about leaving you no space other than the gutter or over the white line. No comm is gonna cite me for riding on the white line leaving you no space in the wind shadow.

 

[S-Express]

Are you assuming contact? I am talking about leaving you no space other than the gutter or over the white line. No comm is gonna cite me for riding on the white line leaving you no space in the wind shadow.

That would be a good time to attack the groupetto then, break it up a bit. But no, I'm not assuming contact - if there was, then your race would probably be over anyway, one way or the other. However, I think you are overestimating the effect of putting someone in the wind, as opposed to the drafting benefit they will (still) receive from staying on your wheel, regardless whether they have the wind on them or not. Obviously the issue is wind-speed/direction dependent (and group-shape dependent), but let's assume that we are moving forward at a greater speed than the opposing headwind/sidewind. Most fit racers could probably cope with that for a while, which is probably why they are in the break in the first place.