they do the tests at 30 mph because that is the industry standard speed setting for the wind tunnel, or at least, the speed that is commonly used, therefore valid for comparison. They then extrapolate the drag coefficients that result from the test based on calculated times assuming a rider with a certain wattage output at that drag coefficient. Or something like that. I think he says he figured 200 watts for the time trial and 150 watts for the Ironman.

In any event, they probably have a set calculation that they just plug the drag coefficient into and it yields an approximate time split, given all other variables are fixed.

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