I'll add more, Yes 26m235 is a frequent poster and has posted that same opinion here.
He ignores the 19.7mph in favor of 15 mph then arbitrarily says that it is actually 9 mph. Then he throws out some reduction percentages due to less wind resistance.
The problem here is that Jonas' calculator already takes into account of less air resistance at slower velocities. 26m235 errs in that he want to double-reduce wind resistance.
The problem
(ventolin had already done this problem before)
A 2:03 marathon is 123 minutes
123 minutes is 7380s
7380/42195 = 17.49 per 100m segment.
Let's go ahead and say that the wind velocity was 9 miles per hour instead of 19 with 31 mile an hour gusts like it was.
I'll use 8.9 miles per hour instead of 9.0 becasue it is 4.0 m/s. I like round numbers.
Go to Jonas calculator plug in 17.49 4.0 20m altitude
http://myweb.lmu.edu/jmureika/track/wind/index.html
You get 0.445 per 100m or
0.445*421.95 = 187s or 3:07
I personally don't like these calculators because it is unknown what the formula is and I think that 3:07 is too high. Secondly who knows how much his math breaks down on the fringes? For the 100m the only factor is how much wind resistance reduces maximum speed. With a tailwind there is less resistance therefor the sprinter can go faster.
With a marathoner he still gets the benefit of a loss of air resistance, making him faster, but more important, he doesn't suffer the cumulative effort of work against that air resistance for those two hours. This is huge.
Jonas calculator gives a 2:03 marathon time with an 8.9mph tailwind 3:07 advantage. I'd bet than his calculator is off of and is only half that, but factoring in the additional benefit of energy not used fighting the air resistance, it's probably a push so we're back to that 3:07 figure again.
I will go on to tell you that I respect 26m235 opinion a lot. He generally plays fair and presents his case, but I think that he hasn't given as much of a look to this as he normally would.
So thanks to djconnel and Giovanni Ciriani for their inputs on this, which I'm pasting directly below:
Assume a human is 1.7 meters tall by 40 cm wide, with Cd close to 1 for a cylinder with normal wind incidence. That's CdA = 1.5 meters squared. Then assume the wind is blowing at around 2 m/sec (very fast for road-level given how fast these guys are running) with an air density near 1.2 kg/m-cubed. That's 6.25 N = 6.25 kJ/km. Minetti measured close to 3.4 kJ/km/km for running:
http://jap.physiology.org/content/93/3/1039.full
. So if a runner weighs 60 kg, that's 204 J/m, of which the tailwind is saving 6.25 J/m, which if speed is proportional to power, is 3.8 minutes saved. (courtesy djconnel).
So that's 3 min and 48 seconds.
And then there is this, the wind resistance and relative velocity argument:
Aerodynamic drag for a runner is about 3% of forces acting against him/her. Today's wind in Boston (according to wunderground.com) was 14 mph W to E, which is just about the same speed the top runners were running at. Therefore the runners didn't experience aerodynamic drag. Since their power output remained the same, a 3% advantage translates directly into a 3% higher speed, and a 3% lower time = 3 min and 36 sec. (Courtesy G. Ciriani)
I'm going to work with an engineer to see if it's possible to refine the assumptions a little and work towards a clearer understanding of the physics. However, we're in the ball park of 2 to 3%, 3 to 4 minutes. Now, let's compare that to performance variations.
JKs pre event guess. 3-4 minutes wouldn't shock him.
My post race guess - 3-4 minutes
according to Jonas calculator 3:08
according to djconnel and Giovanni Ciriani 3:36 aand 3:48
All of us have supplied a rational behind our estimates. The flatearthers only defense is that we hate Ryan Hall, and/or Mutai, or Boston, or else we are bitter and jealous that we can't run 2:03.
ITS THE WIND, STUPID.