Slow vs fast riders
Everyone knows aerodynamic drag increases the faster you go, so an aero bike is important for fast riders. But what about the rest of us?
Let's take a fast rider who can go for an an hour at an average speed of 40km/h. An aero advantage (frame, wheels, helmet) gives him a 2km/h speed advantage. When we give the same advantage to a slower rider, he gains 1.392km/h. So the slow rider gains less speed from the aero improvement. This is as expected, based on the drag equation where drag force goes up with speed.
However, we usually race a fixed distance, not a fixed time. So let's compute how long it takes to ride a 20km TT distance. It’s simple math: To get the finishing time, divide the distance by the speed. For example, if our fast rider goes 40km in one hour, it takes 30min to ride 20km. Do the same for the two speeds, and we obtain this result:
The faster rider saves 1:26, while the slower one saves 1:47! Why does the slower rider save more time? He’s on the course for more seconds, so saves more time overall.