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slipstream questions

Old 07-02-14, 11:42 AM
  #1  
67tony 
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slipstream questions

Is there a website that shows the relationship between trailing distance and drafting efficiency?

And, how about the percentage difference between different riders in a single-line group, for instance the difference between position 5 or 6, compared to position 4, 3, or 2?
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Old 07-02-14, 11:55 AM
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never seen such but that curve will clearly vary depending on the speed of the leading and trailing riders. as to the other question, other than the leader, the effort required for others in the line will be very similar
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Old 07-02-14, 12:36 PM
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Also: effective wind speed and direction and the relative sizes of the riders.
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Old 07-02-14, 12:57 PM
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Originally Posted by caloso View Post
Also: effective wind speed and direction and the relative sizes of the riders.
Yep. Some guys are like drafting a blade of grass. Some guys are like drafting a school bus - sometimes with the exhaust included...
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Old 07-02-14, 01:03 PM
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Originally Posted by achoo View Post
Yep. Some guys are like drafting a blade of grass. Some guys are like drafting a school bus - sometimes with the exhaust included...
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Old 07-02-14, 01:18 PM
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Lol, when there is a big guy in the echelon I also make it a point to draft from him


Also distance matters, some guys like to draft 2 inches away others guys 1-2 feet
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Old 07-02-14, 01:31 PM
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Originally Posted by 67tony View Post
And, how about the percentage difference between different riders in a single-line group, for instance the difference between position 5 or 6, compared to position 4, 3, or 2?
Racing cyclist power requirements in th... [Med Sci Sports Exerc. 1999] - PubMed - NCBI
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Old 07-02-14, 01:37 PM
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It's a good question and I've wondered myself. Say, outdoors no wind and everything else being equal how does it drop off with distance? Proportional? Square of the distance? Step function? I'm pretty sure of a noticeable draft boost even 5 or 6 bike lengths back, and I'm guessing that if you're close enough it doesn't make a whole lot of difference from an inch to a foot. I could be wrong. Surely someone at some time has put together a decent approximation.
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Old 07-02-14, 02:44 PM
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Too many variables, but this is probably close (unless you're waving).....
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Old 07-02-14, 03:02 PM
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Originally Posted by FLvector View Post
Too many variables, but this is probably close (unless you're waving).....
Informative. But, the draft is improved by the intervening bodies between the drafting bike and the leader (else it wouldn't drop to 64% further back) so the effort level of just one rider drafting at a given distance would be something somewhat higher than the chart.

In other words, the third guy at 64% in the paceline, if he didn't have the guy at 71% in front of him, would have to have an effort level higher than 71%. 80, 90% something like that. Then the fifth guy, with no one between him and the lead, would be even worse.

Waving, have the whole pace line wave in unison. I'll bet that the waves would have their own little drafting effect.
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Old 07-02-14, 03:15 PM
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The graphic above is meant to show the percentage difference between different riders in a single-line group at the different positions 1,2,3 etc., and the effort when in these positions. It's not meant to show the drafting efficiency without riders in their respective positions. It shows that after the position of the 3rd rider, the drafting effect is essentially the same as the riders behind them, which is often what I experience. Again, lots of variables to consider.
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Old 07-02-14, 03:26 PM
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Originally Posted by FLvector View Post
The graphic above is meant to show the percentage difference between different riders in a single-line group at the different positions 1,2,3 etc., and the effort when in these positions. It's not meant to show the drafting efficiency without riders in their respective positions. It shows that after the position of the 3rd rider, the drafting effect is essentially the same as the riders behind them, which is often what I experience. Again, lots of variables to consider.

Right, I was extrapolating. About the only thing to deduce (in the latter case) is that someone in the number 3 spot gets something less than the 29% reduction in drag. That's more information than before though.

I just realized that the chart explains something else, the big complaint in drafting threads about someone in front of you gapping. Aside from the obvious that you have to make up the lost ground some time. Number 3 guy, who is now number 2 in the sub-pace-line when number 2 lets a gap form, suddenly sees his effort level jump from 64% to 71%. The guys behind him don't care as much except for getting yo-yo'd.
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Old 07-02-14, 03:40 PM
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Originally Posted by wphamilton View Post
...

Waving, have the whole pace line wave in unison. I'll bet that the waves would have their own little drafting effect.
if going to the trouble to incorporate synchronized waving, might as well optimize it and carry some carbon one-armed ping-pong type racquets to paddle your way along, in sync of course. no point in wasting energy.
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Old 07-02-14, 03:48 PM
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Originally Posted by hueyhoolihan View Post
if going to the trouble to incorporate synchronized waving, might as well optimize it and carry some carbon one-armed ping-pong type racquets to paddle your way along, in sync of course. no point in wasting energy.
That evokes an awesome mental image. That could also serve to optimize the signals they seem to be fond of.

And is it possible that the rackets could act as vortex generators, pulling the divergent air flow back to the composite pace-line object, actually improving the aerodynamics? Has anyone actually tried this and measured the difference?
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Old 07-02-14, 04:18 PM
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Originally Posted by FLvector View Post
Too many variables, but this is probably close (unless you're waving).....
I'm pretty sure Broker only looked at four riders total.
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Old 07-02-14, 04:36 PM
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Originally Posted by wphamilton View Post
That evokes an awesome mental image. That could also serve to optimize the signals they seem to be fond of.

And is it possible that the rackets could act as vortex generators, pulling the divergent air flow back to the composite pace-line object, actually improving the aerodynamics? Has anyone actually tried this and measured the difference?
the possibilities are vast and complex as your imagination.
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Old 07-02-14, 05:02 PM
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Originally Posted by wphamilton View Post
It's a good question and I've wondered myself. Say, outdoors no wind and everything else being equal how does it drop off with distance? Proportional? Square of the distance? Step function? I'm pretty sure of a noticeable draft boost even 5 or 6 bike lengths back, and I'm guessing that if you're close enough it doesn't make a whole lot of difference from an inch to a foot. I could be wrong. Surely someone at some time has put together a decent approximation.
5 or 6 bike lengths would be 8.5-10 m, I don't notice any drafting at that distance (at least at my moderate speeds, nearly always below 40 kph), but 1" (well, 2"...) distance is clearly different than 1' IME.
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Old 07-02-14, 05:16 PM
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Not sure of the exact numbers but it feels easier drafting "Big Bill" verses Dr. Mike (the hobbit)

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Old 07-02-14, 08:09 PM
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When you're at the limit, 5 bike lengths may as well be 5 miles.
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Old 07-03-14, 05:52 AM
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Originally Posted by caloso View Post
When you're at the limit, 5 bike lengths may as well be 5 miles.
+1

I found this informative...How to Draft and Ride in a Paceline | Bicycling Magazine
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Old 07-03-14, 06:09 AM
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Originally Posted by wphamilton View Post
That evokes an awesome mental image. That could also serve to optimize the signals they seem to be fond of.

And is it possible that the rackets could act as vortex generators, pulling the divergent air flow back to the composite pace-line object, actually improving the aerodynamics? Has anyone actually tried this and measured the difference?
And to bring in the thread about breaking in a paceline, the rackets could be used to give you your minor adjustments in speed when you're getting too close.
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Old 07-03-14, 07:36 AM
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What if everyone was waving synchronized ?
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Old 07-03-14, 08:34 AM
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Originally Posted by caloso View Post
When you're at the limit, 5 bike lengths may as well be 5 miles.
+2. I recall Flecha saying he was at the back of a group, 1 km remaining, at about 50 kph, he stopped pedalling for a second to avoid a pothole, a very small gap formed (1 bike length at most), he was dropped.
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Old 07-03-14, 08:37 AM
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Riding at your limit behind a fast pace line sure, I'd imagine that you'd need all the help you can get. But are you all saying that there is no draft at all at 5 bike lengths back?
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Old 07-03-14, 09:20 AM
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Here's another graphic showing the drag reduction of the cyclist's position in the group.

Regarding how many bike lengths behind the cyclist does the slipstream disappear, this would be relative to the speed and distance you follow. There's no simple answer since variables such as the size of the cyclist in front, amount of crosswinds to diminish the slipstream, how many cyclists are up front creating the slipstream and how many abreast are they riding, etc. I've noticed the drafting effect diminishes quickly after 2-3 bike lengths back behind a single cyclist, but don't have any numbers to quantify. If I'm looking for the draft advantage, I won't drift any further than one bike length if I can help it.
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