b'Engineer Innovation | Sport SciencePressure Coefficient1.00.60.2-0.2-0.6-1.0Baseline Car Only Pacers only Pacers + CarFigure 3: Drag force acting upon Kipchoge in each of the four scenariosof the four scenarios. The dark blue areasshould be available for him to transfer to show areas in which the air velocity isthe road surface, and in principle run less than five miles per hour (mph). Infaster. See figure 4.both the cases with pacers, Kipchoge is running into a five mph "wind" despiteGiven that Kipchoge is capable of traveling at almost 13.1mph. running at roughly about 300 watts (W), the difference between undrafted and From the plots of velocity, you can seefully drafted scenarios is around 31W, that the pacers do a great job ofmeaning that he can probably devote an shielding Kipchoge from the wind. Ourextra 10 percent of his effort to running calculations suggest that the only realfaster in the latter case.benefit of the car and timing combination is in preventing KipchogePerhaps surprisingly, most of that saving catching the wind in his face. The wakeis generated by the close delta formation behind the timing board tends to skewof pacers around Kipchoge which upwards more because of the high- generates a 28W saving even without speed flow beneath the car (which has athe car, which only adds another 3W to flat floor) expanding as it exits thethe total.diffuser and the chasing pack has a higher pressure zone ahead of it, whichBecause power output varies with the then diverts the flow around it. cube of velocity it is possible to estimate the amount of time saved in comparison More usefully, we can integrate thewith the undrafted runner. Our pressure acting over the surface of ourcalculations suggest that the pacers virtual Kipchoge, and calculate the dragsaved Kipchoge about 4 minutes and 9 force acting upon him in each of the fourseconds compared with a solo runner, scenarios. (see figure 3) and the pacers and car combination saved him about 4 minutes and It is easier to interpret these results if we35 seconds.consider the energy required to overcome drag, which is the forceThe undrafted case is an absolute worst-acting on our Kipchoge, multiplied by hiscase scenario (other than perhaps forward velocity (just under 13.1 mph).running into a headwind). Elite The energy that Kipchoge saves in notmarathon runners do not set world having to overcome aerodynamic dragrecords while running alone, typically 12'