Effects of draft in large group
 

Question for all of you aerodynamicists out there. If you have identical riders, on identical bikes, identical aero position..... you get the point a bunch of identical folks. How much faster, if any, would a peloton of 50 riders be than a small group of 3 or 4 if the lead riders in both groups are putting out identical watts.

No faster at all, in the short term. But much faster over a period of time, because there are more riders to share the work and those in the middle of the pack will stay fresher because they are better protected from the wind.

5 mph. 15 mph. All in between.

Every single rise or roller will be significantly faster every single time as there's just so much more speed and momentum.

Headwinds and false flats will also be significantly faster short and long term.

Explain the headwind and false flats if you don't mind. Remember, I'm saying the ones doing the work in both groups are pulling at identical watts. I didn't say it before, but I'm meaning consistent power output also.

I'm really trying to narrow it down to how much, if any, benefit where is aerodynamically from the folks riding behind you. Is the more the merrier/faster?

Benefit from folks riding behind you? None. From folks riding in front? Huge. Say you're in a pack of 50 riding at 40kph. The guy or gal at the front will be turning themselves inside out, tongue dragging on the wheel after a few minutes. The riders at the back will be coasting half of the time, eating little sandwiches, and yakking about the movie they saw last night.

Try a site called: 'bikecalculator.com'. You can enter various combinations of speed, headwinds and wattage. The effect of wind pressure is easily apparent, both in theory and practice.

Folks riding behind you can capture some of the airflow coming off your back, preventing it from swirling behind you and contributing to the low-pressure area suctioning you backwards. But IIRC, even the difference between zero and one drafter tends to impact air drag on the order of only a couple percent. I doubt 4 riders versus a peloton has much impact, especially if we're not assuming different immediate formations around the leader.

A consistent wattage is absolutely pointless. It completely negates the entire point of the peloton.

In huge fields you're not even consistently pedaling in the draft. You're just sucked along. In a 4 man group you're pedaling constantly. You may take 400 watt pulls and then do 400 to get back in the draft and then continue doing 250-300 as you're moving back through. In a huge field you might do 500 for a few seconds and then simply coast for 20-30 secs as you drift back and then swing in and pedal at 50-100 for a bit.

It's a massive, massive difference.

Maybe there's some effect, but a rider in front of a pack of 10, 20, or in front of only 3, putting out the same watts, will go the same speed, so the riders behind him will go whatever that speed is. Is this a trick question?

The title of the thread says "effects of the DRAFT" and then the op says how much faster is a peloton versus a small group. The answer to that is significantly, significantly faster.

The qualifier of "at the same" wattage makes zero sense in application as it completely negates the point of a small or even large group. Might as well compare individuals at that point. And it has nothing to do with the thread title.

At first this was kind of confusing, but then I realized a lot of it was only an attempt to say "all else being equal except the number of riders in the peloton " in other words, does the size of a peloton provide an advantage. I believe the answer is yes, especially when the peloton is a few riders wide, because drag is more dispersed. If you're talking about a single paceline, the guys in the back are NOT having lunch and chatting while the rider in front is working his guts out.

When you see everyone single file in a race, they are all working, maybe not as hard as the one at the front, but the guys in the back could be hanging on for dear life. When they're bunched up, sure, have a snack, take a break, whatever. Of course that's about more than just the effects of drafting, but that's part of it.

So you think the question really is asking how much faster would the riders be going that are leading because of reduced drag, in front of a large group, vs. a small group? (with same wattage output for either scenario). It has to be pretty negligible i would think, and per Rubik's point, it's not the point of a peloton.

If the lead riders never changed, then it would seem that would equalize the large and small groups as they don't benefit from more people behind them but that would be unlikely as the riders behind putting out less effort would naturally overtake the lead at some point.

Consider a formation where the front is a sort of triangle, with the center rider's sides protected by riders slightly behind. If the drag caused by loose clothing is enough to make a difference in a TT, eliminating the drag on the front rider's sides would seem to provide a similar benefit.

Since you stipulated the lead riders (who are setting the pace) are identical in power and aerodynamics, there will be a speed difference only if 49 trailing riders reduce the drag of the lead rider more than the 3 trailing riders.

The difference between a peloton and a small group of riders is a LOT if you are talking about the rider with 50 in front of him vs 3. I don't know the numbers, but it's an order of magnitude, not small. Now there are real drawbacks to sitting in the middle if it is a race, Accelerations string things out and the further back you are, the harder and longer you have to keep the high pace up to close when it slows down. But for steady speed, those in the midst can just cruise. In the front 10 or so riders, the work is real. (I rode a race with a 120 man field that averaged a hilly 105 miles just under 27 mph. I spent time in a 6 man break, the first 10-15 riders, the middle of the field, the 30 man split off the front and about a mile chasing that split. Hard, hard race. But the time I spent sitting in the field was recovery time (at probably faster average speed than the time I spent in the 30 man group).

I've never seen numbers on this, but we all knew that a big cloud of air moved with the peloton. Sitting far enough back, you were in it and life (at least as a trained bike racer) was easy.

Ben

I understand everything you say, but the consistent wattage is the only way I knew to set the parameters for my question. So it wasn't pointless in the context of my question. Others have answered the question I was after & curious about.

Exactly. Do you know if 49 trailing riders do reduce drag more than 3 trailing riders? This really wasn't a question where I'm trying to get any benefit from an actual ride. I was just curious & didn't know the best way to ask.

Some perspective:

"Bert Blocken came to a similar conclusion in his 2013 study on the aerodynamic drag of two drafting cyclists. Blocken wanted to find the optimal strategy for team time trials and how all riders could be used to full effect. He found that in a four-rider paceline, the lead rider’s drag is reduced by about 2 to 3% compared to if they were riding solo. The second rider in line experiences a reduction of about 27% while the third and fourth riders see drag reductions of approximately 35%."

I'm sure 49 trailing riders offer more benefit than 3 or 4, but I'd wager it isn't a big difference.

Go watch a road race on a smaller circuit. The Redlands Classic has a stage in my town, 20 laps of a ~2.5 mile course. I've watched a 3-7 man breakaway lead out by over 2 minutes, only to watch the peleton reel them back in less than a lap.

This year, the Cannondale team was setting the pace in the men's race for about the first 17 laps, and had broken the field into two groups. Then the main group decided it was time. Caught the lead pack, and spit them out the back with one to go.

I don't think anyone from Cannondale finished in the top 50. I've only seen a successful breakaway a handful of times. The group of 50 is a much bigger machine, and will take down that group of 3 nearly every time.

I'd wager that the advantage of the wedge that a peloton makes provides more advantage to the lead rider than having a straight line behind him. I'd wager it's at least double, i.e., 5-6% compared to riding solo - wouldn't be surprised if it was 10%. But even if it was only another 1%, if it's reliably measurable to that extent, it may not be a big difference, but it is significant. A minute faster in 100 minutes is not nothing.

The biggest contribution will be from the rider directly behind the leader. You're not going to quadruple the effect by adding riders further behind and offset from the leader.

You're not far off. The study mentioned earlier by Bert Blocken showed with one rider directly behind the lead rider he would experience 98% drag vs 96% for two riders behind.

https://cimg7.ibsrv.net/gimg/bikefor...2a7b180375.png

Was reading the thread and waiting for this to be mentioned. Good topic. Its big. Proven in grand tour races throughout the world every year. 4-7 man breakaways get pulled in by the big collective peloton. Big difference in watts, recovery and power sharing.

Actually, I wasn't talking about having more riders further behind as in a) and b) above, I was talking about having a wider front, i.e., riders flanking the one on the point of the wedge, like this:
https://cimg1.ibsrv.net/gimg/bikefor...1b247c9db0.jpg