On bicycles.se a question came up about whether one cyclist drafting another cau

Question

On bicycles.se a question came up about whether one cyclist drafting another causes the lead cyclist to be slowed down. A contributor suggested that the opposite might be the case, that the leading cyclist would be 'helped' too. Clearly, in the real world of cycling there are winds, potholes, traffic and other variables, plus the lead cyclist would not necessarily notice a small bit of extra help. Therefore 'probably not' is not the answer I am looking for, a bit of theory would help.

Another 'drafting situation' happened at Monza today in the qualifying for the F1. The Ferrari team had one of their cars give the other an aerodynamic tow along one of the straights, this helped their number 1 driver get to 4th on the grid, a position he would not necessarily have achieved otherwise, in a race where fractions of a second do matter. If you can better visualize F1 cars than bicycles, then today at Monza is another situation where drafting went on. We know it helps the guy behind, but does it also help the guy up front?

Explanation / Answer

Following closely would speed up both vehicles in certain cases. Consider two cylinders following each other, end to end, at 100 mph, 1000 feet apart. Each cylinder would have a lot of air resistance.

Now consider the cylinders following one another at 1mm separation. The wind resistance will be less for the second cylinder because it's not getting hit in the face with all the wind. There will be less resistance for the lead cylinder because there is no suction to speak of pulling back on it. So the two cylinders are more efficient when they're 1mm apart.

The same thing would apply to cars, depending on shape, separation, and speed.

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