It is really hard to guess at that. For instance at Austin 70.3, the width of the roads and turns usually means you get slowed down by the people you are passing rather than sped up. You may also have to surge a little bit to pass in the 20 second window at times which costs energy.

I can tell in my wife's power file where she finally got through all the traffic, and was able to settle in to a much more steady power output

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Apologies - I know you asked for quantifiable data.

I swam a 1:18 and biked a 5:08 and more or less passed 600+ people and maybe got passed by 5. My friend and training partner rode a 4:59 (includes 5 for drafting penalty). I strongly believe that a 13 minute gap between us two is reasonable (i.e. no meaningful slingshot effect). If I had a bigger slingshot advantage, I would have expected to be closer to 5 hours.

Also, if there is a draft benefit I think it pales compared to benefit of 'sitting in a group' that sets a pace you can follow for the whole bike portion. I think it is mentally taxing passing people the whole bike portion.

-B

Fair enough, but this is an educated guess. Assume I am rider 1000 and my wind blockers are spaced 25 meters apart stretching around 16 miles when I start my 70.3 bike leg. Assume they are all riding about 20 mph constant and I am riding 28 mph so I will eclipse every one of them by the finish. I think this equation is solvable, I just know nothing about cdA and all the cycling stuff that benefits you in terms of speed/wind yaw, other jargon etc.

Fair enough, but here is some (equally weak) contrary evidence. One of the big slingshot debacles I remember on ST was when age grouper Drew Scott won Buffalo Springs with a ridiculous bike split. He outsplit Joe Umphenour by 7.5 minutes on the bike. At 70.3 Austin last weekend, Drew outbiked him by only 3 minutes racing Pro. Assuming Joe was sitting in a legal draft on both occasions, while Drew was only on the second occasion, and they put out equal power, and the courses are equal, and the winds were the same, etc. etc. I know this is weak...but you get the point. Enough of these examples and we may get a handle on the slingshot effect, which I think is pretty substantial frankly

I have no doubt the slingshot is a valuable benefit of tanking the swim.
I have no clue how you would control all the variables to even throw a rock at a guess to what the value is.

For me, I think the biggest benefit is between the ears.
I usually am solo by mid-ride. Once I am out of traffic, I FEEL a big difference mentally not having rabbits to chase as often. I end up using the power meter as a leash while I am moving through the field, but it becomes a whip once I am solo.

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@christopher_borden •
Spinning Spoke • Dimond Bikes • Flo Cycling • Castelli Cycling

Based on my exp in a WTC-crowded race, it's way too hard to try and get any sort of precise figure because it's in a nearly constant state of flux. Not only do you get the slingshot from overtaking slower riders, but faster riders overtaking you as well (at least a few of them); there were several segments where riders essentially formed 3 columns while appearing to do an honest job of trying to maintain proper spacing: a roughly 18-20mph 'slow' lane, a 21-23mph passing lane, and a 24+mph 'express' lane. Every so often it'd suck getting stuck in a slower lane waiting for a break in the next faster lane to get around, or try to pass someone slower and then find yourself having to maintain the surge much longer than you'd expected to continue overtaking the next guy and the next without blatantly cutting back into someone else's draft zone before you reached the front of the line. (I'm not talking about other cases where I saw people in a huge pack that clearly didn't give a shit to even bother attempting to space out and follow passing protocol, etc).

...But then on the flip side that benefit becomes a handicap when riders inevitably bunch up at every aid station or significant turn, etc, after which it takes even longer for the 'slinky' to un-bunch. And, there's the case when somebody overtakes you and then proceeds to cut in and let off the gas so suddenly you have to brake, or else you have to re-pass without dropping back the prescribed amount first because you're afraid of causing a collision with another rider you just passed yourself who wasn't going that much slower and would now be coming back up on your rear wheel again. It was more mentally draining having to constantly worry about trying to maintain this 'encroachment buffer' around you at all times than it was physically taxing. I won't be signing up for one of those again; if & when I ever decide to do another IM, it'll be a much smaller independent or at least a Challenge race with a somewhat smaller field and wave starts.

I'm a 1:10 swimmer and have similar experiences once out on the bike. the PM is a godsend for keeping things sensible

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I reject your reality and substitute my own!
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I did the B2B half on Saturday. I am a slow swimmer but came into this race with a much better bike than before. I constantly made passes for most of the event - I "think" I got help by riding up and around and to the next rider. I "felt" the slingshot effect.

I think it'd be pretty easy to put together some formulas in Excel that calculate this from a theoretical standpoint, but I also think it'd be totally worthless... Too many variables to actually be worth anything practically. I did Austin 70.3 on Sunday... I started in one of the latest waves and am a shitty swimmer / decent cyclist (2:32) so I had the pleasure of passing a fair amount of people. All in all, I'd say it negatively impacted my time if anything. I would guess there were only maybe 10-20 people I passed where I got real aero benefit. On the flip side of that, if you count all the hold ups due to passing difficulties (narrow roads, people on the left, etc...), I don't think I broke even. In a smaller race, or a race where everyone was riding closer to the same speed I could see the calculations getting somewhat more practical, but still not really all that close...

Too many variables, but my guess would be as much as 1.0 mph in speed for aggressively executed passing relative to no passing shields at all. I perceived roughly this amount of benefit in a race I had ridden several times in practice and often had ridden at close to race power, with only other race differences being other riders on course, aero helmet and, of course, differences of wind on the respective days (but don't remember noticing much wind on either occasion).

Training ride of course @22.4 mph /238W: http://connect.garmin.com/activity/202133754
Race on course @23.6 mph / 240W: http://connect.garmin.com/activity/228830334

Do not know how many people I would have passed on the bike, but probably around 1k.

I did three solo training rides of the Whistler IM course. On the training rides I cut the course short by about 1km. These came to:

5:28 on 204w avg NP 1.09 VI
5:35 on 197w avg NP 1.11 VI
5:43 on 194w avg NP 1.05 VI

On race day I swam 1:13 and had a slow T1. Not sure how many people I passed, but it was a lot - I didn't catch up with people going my speed until 2.5 hours into the ride. Time:

5:18 on 204w avg NP 1.07 VI

Rode the same bike, same wheels, same clothes and helmet. So all other things being equal, the effect of slingshotting was 10+ minutes for me.

Edited to add VI.

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Graham Barron Design: Custom west coast house design http://www.grahambarron.com/

Interesting idea to quantify. I would start by saying the the smaller the delta velocity (difference) between the two riders, the longer you would stay in their draft zone, thus the greatest benefit. Blowing past someone going 20mph when you are riding 28mph probably has a limited benefit. Given that a rider must pass within 20s and that a legal distance behind the rider is 4 bike lengths (7m), it seems like the delta velocity could be calculated to stay in the draft zone for the maximum allowable time. D = V x T. V = 7m/20s= 0.35m/s ~ 0.8mph.
Now to determine the watts saving for a given rider, I would think you would need to do some real world testing of how many watts are saved during the pass versus maintaining that speed without draft and multiplying by the number of riders passed. That's is why nobody has probably tried to quantify this, because the variable speed of riders and time to pass would be too difficult to quantify. My 2 cents.

now that is some good data. same tires too?

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Yeah but were all other things equal? Even wind stronger by a few mph could conceivably account for that difference. Also there are a lot of interesting things you could say about average power too; for example, was there more variability on one ride vs. the other?

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I think this was covered a few years ago in some detail on David Wardens Tri-Talk podcast. IIRC it was a nice benefit to both riders. David K

You can plug in my name into sportstats and see all my Demi Esprit half IM bike splits. This is a race run on a formula 1 race track in Montreal, for 20 loops of a 4.2K loop, plus an out and back. Total bike course is just under 89K so let's add a couple of minutes to those splits. My bike times there have ranged from 2:09 to 2:20 depending on how the wind is flowing. This is also the only truly flat race I have done. The other faster courses have been Timberman and Tupper Lake. Off the same watts at Demi Esprit, I am generally around 10-15 min faster than other half IM's....let's say 2-4 minutes due to no hills, the rest froma continuous slingshot. I'm generally riding there at 45-50 kph in the tailwind sections and 35-38 kph in the headwind/sheltered...add in the braking and you get bike splits that are ridiculously fast. Some of it is flat, some of it is pavement, some of it is shortness of the course. But MOST is from continouslyly slingshotting riders who are going 5-10 kph slower. The slinghshot effect is insane. Timberman/Tupper Lake caliber courses, 2:25-2:31 range. All of this off the same wattage range and similar set ups. Slingshot can be huge. Clearly the demi Esprit times are huge outliers to my normal times. Guys like MTL, Murphy's Law (did a 2:05 the year I biked 2:09) and Desertdude also have data to show how much of an outlier than Esprit Slingshot ride is. Yeah, we love it because it is super fast and you legally get a fast time, but none of us are fooling ourselves that we're pro zone. the entire course may as well have a tailwind (kind of like those point to point marathon courses that are done with a net downhill and prevailing tailwind to help people get BQ times).

Could it be estimated by assuming 10 seconds of draft per rider passed times the number of riders passed to get the total time of getting a draft effect and then factor in the speed differential at constant power output when drafting versus when not drafting (not sure what that would be, but approximations must exist)?

There was a ST feature article that included a spreadsheet with detailed breakdown of the IMMT 2012 race - not sure where that is now, but I recall it showed me passing about 1,000 riders (terrible swimmer and decent cyclist). My bike time was at least 10 minutes faster than I could have hoped for, and I attribute that solely to the slingshot effect.

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"No more hurting people - Peace"

Good point. Also did he have his race kit on in traiing ride? Same helmet? Was he in the aero position more in the race vs. training? Did he brake less on downhills in training or have to stop for stop signs, intersection, etc. Stopping to use the bathroom? Basically, the VI on both efforts needs to be the same to compare fairly.

I know when I compare training rides to races, one HUGE difference for me, is the roads in my town on the first 2 miles are terrible, limiting my speed and I have 4 stop signs and 2 stop lights. It adds up to a couple minutes. Then I might pull over to pee a coupel times too.

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TrainingBible Coaching
http://www.trainingbible.com

You could do a "napkin" calculation as follows: (too busy to look up all the variables)

Assume a speed of the riders being passed.
Assume a time that the person passing would spend in the draft zone.
Assume a power for out of the draft and in the draft.

Now calculate the power saved by sitting in the draft zone for the legal time.
Calculate the acceleration and speed that the passing person would achieve if they went to the non draft power in the draft zone.
Calculate how much time is saved as that additional speed decays after the person passing leaves the draft zone.

Now you have a time save and watts saved for each pass. Estimate a number of passes times the time saved, and how much extra effort you can put out based on the saved watts times number of passes and you have your answer.

As you can see, with that many "assumes" and "estimates" in the calculation it would be little more than a WAG.

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"...the street finds its own uses for things"

A few things... vi identical? same amount of time in aero? same amount of slowing for turns/stopsigns/lights? slowing/stopping for water? same wind?

It seems like there's a lot of things that can't be measured.

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Wasn't the wind coming back in to Whistler really calm for IMC? I hear it is regularly a very strong headwind as you climb back in to town. I would think a windless day would be far more to blame (or in this case, thank!) then the sling shot effect.

Also, I would like to add that slingshotting can help faster swimmers. I am a relatively strong swimmer and weak cyclist. I get out in the FOP and the first 3rd or so of my bike leg is spent watching the speedsters blow past me like I'm standing still. I'm pretty sure I'm getting a substantial benefit from their passing and being in their wake as they ride away. If it was one or two guys, I'm sure it's not a big deal, but when it's 100 guys, that is a lot of time spent getting some unintended drafting benefit.

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Long Chile was a silly place.

Yes, same tires. Conti GP 4000 S.

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Graham Barron Design: Custom west coast house design http://www.grahambarron.com/

I edited my post to add VI. The last ride was lower mostly because I was trying to reduce VI.

Similar amount of time in aero. The training rides were unsupported so I stopped for drinks, and stopped the garmin during stops. The training rides were windy and the race wasn't. Not sure how much the wind would affect it, since it was a tailwind in one direction and headwind in the other.

Yeah it's not very scientific data, but it's something.

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Graham Barron Design: Custom west coast house design http://www.grahambarron.com/

You dont wear your aero helmet in training?

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"One Line Robert"