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drafting

Old 05-15-19, 12:38 PM
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HardyWeinberg
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drafting

Interesting article on drafting in swimming; not only can you reduce your workload by 30% if you are following someone in the right location, but you can also steal some of their laminar flow and inflict extra work on them

https://www.nature.com/articles/d41586-019-00279-7

I figure air is not viscous enough for drafting a rider to cause that rider to work harder, but I guess I never really thought about it.
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Old 05-15-19, 02:13 PM
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Originally Posted by HardyWeinberg View Post
Interesting article on drafting in swimming; not only can you reduce your workload by 30% if you are following someone in the right location, but you can also steal some of their laminar flow and inflict extra work on them

https://www.nature.com/articles/d41586-019-00279-7

I figure air is not viscous enough for drafting a rider to cause that rider to work harder, but I guess I never really thought about it.
I read years ago that drafting actually *helps* the rider in front ... but only by about 5%. That makes sense to me, as it should be like having a boattail or other structure behind the rider and decrease reynolds flow behind them.
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Old 05-15-19, 02:34 PM
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Originally Posted by Biker395 View Post
I read years ago that drafting actually *helps* the rider in front ... but only by about 5%. That makes sense to me, as it should be like having a boattail or other structure behind the rider and decrease reynolds flow behind them.
I remember reading something similar myself.
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Old 05-15-19, 02:53 PM
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Originally Posted by Biker395 View Post
I read years ago that drafting actually *helps* the rider in front ... but only by about 5%. That makes sense to me, as it should be like having a boattail or other structure behind the rider and decrease reynolds flow behind them.
That was my first thought also but it's a different situation. We help the lead cyclist by filling the low pressure area behind him (where the air swirls, but we're redirecting it around us instead).

This article cites the bow wave in the water as disrupting the laminar flow on the lead swimmer's body, and that seems reasonable to me. We have that in the air also, but I've seen it calculated as a matter of inches ahead or less at bike speeds - and when I originally saw that calculation I wondered "how can that possibly help the lead rider"? The answer is, it's not the bow wave that does anything to him.

The difference, I'm fairly sure, is that we're looking at two different things having the impact. In the case of the cyclist it's the low pressure turbulence behind him that we're interfering with, which helps him. In the case of the swimmer it's our own bow wave interfering with the flow against his body, which hurts him.
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Old 05-15-19, 06:08 PM
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My wife and I ran the cycling case at Velo Sports Center during an aero testing session. When I ride behind her, I lower her CdA and the result was consistent riding around the track as ERO measured her CdA in real time.

ERO has the capability to monitor 4 cyclists on the track and allow an optimization of rider positions in team events.
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Old 05-16-19, 09:05 AM
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Originally Posted by wphamilton View Post
That was my first thought also but it's a different situation. We help the lead cyclist by filling the low pressure area behind him (where the air swirls, but we're redirecting it around us instead).

This article cites the bow wave in the water as disrupting the laminar flow on the lead swimmer's body, and that seems reasonable to me. We have that in the air also, but I've seen it calculated as a matter of inches ahead or less at bike speeds - and when I originally saw that calculation I wondered "how can that possibly help the lead rider"? The answer is, it's not the bow wave that does anything to him.

The difference, I'm fairly sure, is that we're looking at two different things having the impact. In the case of the cyclist it's the low pressure turbulence behind him that we're interfering with, which helps him. In the case of the swimmer it's our own bow wave interfering with the flow against his body, which hurts him.
Gotta love this place ... only here can you get into a discussion about laminar flow and bow waves.
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Old 05-16-19, 01:21 PM
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Being a big guy, I often have folks latch on during group rides. I can promise it makes no discernible difference in my effort to hold speed. Theoretical truth does not always translate to real world situations as it does not calculate all conditions on the road, like the effect of cross wind. Maybe on an indoor track.
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Old 05-16-19, 01:28 PM
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Originally Posted by Biker395 View Post
Gotta love this place ... only here can you get into a discussion about laminar flow and bow waves.
Gotta love this place..... only here can we buy into theories (or realities) that have no real effect on our riding performance or satisfaction.

But I'm not opposed to investigation and 'pure' science.

Now where are those aero shoe covers of mine.
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Old 05-17-19, 12:36 PM
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Originally Posted by Biker395 View Post
Gotta love this place ... only here can you get into a discussion about laminar flow and bow waves.
Dad gum engineers and scientists.....oh wait!!!
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Old 05-17-19, 12:49 PM
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Originally Posted by Biker395 View Post
Gotta love this place ... only here can you get into a discussion about laminar flow and bow waves.
and reynolds flow!
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Old 05-17-19, 04:37 PM
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Several years ago .. on US 101 going down the coast,

Wind shear /bow wave off a passing semi, * knocked an elderly rider off his bike ,

he fell to the left and was run over by the trailer back wheel. ...

* A motor home can knock you off too ...
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Old 05-17-19, 06:51 PM
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And the latest on racing says the best place to be to save energy in the peloton is smack in the middle of the pack, where you expend a tiny fraction of the energy of the outside riders. But it's also more demanding of bike handling skills and situational awareness, so I wouldn't do that unless I absolutely trusted the riders around me.

In actual practice if I ever draft nowadays it's only when I've fallen off the back and a friend is towing me back. I don't mind if someone drafts me but they'll be disappointed in how slow I am.
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Old 05-18-19, 12:31 AM
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Originally Posted by fietsbob View Post
Several years ago .. on US 101 going down the coast,

Wind shear /bow wave off a passing semi, * knocked an elderly rider off his bike ,

he fell to the left and was run over by the trailer back wheel. ...

* A motor home can knock you off too ...
Not a semi and not a coastal state, but there was this case: Cyclist killed after aerodynamic design of bus caused him to be sucked under vehicle. It's probably under appeal now.
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Old 05-20-19, 10:22 AM
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Whether it does or doesn't is really not important. What is important in the overall energy savings of the group of riders. And any strategy that one might try to base on such still has more to do with the drafting rider saving energy than the drafted rider losing more energy.
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Old 05-20-19, 11:09 AM
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Back in my swimming days, I knew drafting someone worked just like in cycling. But I wonder about affecting the front swimmer. It never affected me enough to notice. In competition there are lane lines to minimize wakes and you have to get really close to take advantage. It only works when both swimmers are crowding the same lane line.
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Old 05-20-19, 01:31 PM
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Originally Posted by HardyWeinberg View Post
and reynolds flow!
Would that be 531 or 753?
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Old 05-20-19, 01:38 PM
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Originally Posted by John E View Post
Would that be 531 or 753?
I don't know about the relative viscosity of the different alloys at different temperatures...
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Old 05-20-19, 01:47 PM
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Burt or Ryan?
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Old 05-20-19, 02:31 PM
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Triathletes draft all the time in the swim leg. Is also why we switch leads in a lap pool workout, those following have it easier.
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Old 05-22-19, 09:44 AM
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Drafting while swimming in triathlons is where this usually raises its head (pun intended). Has anyone here besides me actually tried to draft in OPEN WATER? You can't see four lengths ahead of you unless you raise your head in most open water situations, at which point your drag increases and your body tries to sink. Drafting in open water is extremely difficult for most age groupers, IMHO.
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