It comes up with such frequency, and is debated with so much passion, that it may be one of the most important questions in the sport of cycling, yet no one has really examined it scientifically. Until now.
The roadie in full regalia, his steely gaze is focused and intent, you give a wave and you're ignored. What's up with that? Would it really hurt him to wave? That's usually a rhetorical question but I set out to find an answer. What does it cost him to wave?
So I took my road bike to a local hill to perform some coast-down tests while simulating a roadie in training. I selected a hill with a relatively gentle grade so that speeds would be similar. In half the tests I coasted in a regular roadie position, and in half I waved all the way down while trying to maintain the same position. I wanted to make the simulation as real as possible so I wore an actual jersey, tight, and spandex cycling shorts. Helmet, sunglasses. All tests were with hands on the hoods (since careful observation has indicated that training roadies ride on the hoods, or with the same back angle while in the drops).
This is the test rig: bike.jpg bike.jpgalthough it's Fredded up it is, as you can see, a road bike with standard road bike geometry, normal saddle to bar drop, 700x25c tires.
To complete the simulation I strapped on a HR monitor and also turned on Strava, as if I were doing hill repeats. For you doubters out there Bike Ride Profile | Coast-down test repeats near Alpharetta | Times and Records | Strava although I didn't use Strava data since my flight recorder box is more accurate. I did three tests coasting, three waving, with no pedaling at any time. Except uphill of course. I started each test at precisely the same point in the road, with the magnet positioned 1/8th of a wheel behind the sensor.
I threw the second waving run out because passing traffic distorted the data. The final repeat in Strava was not a test run - I just did it because just coasting is pretty boring. Here is the result:
The vertical axis is miles per hour, the horizontal is units traveled (unit representing approximately 7 feet, one wheel revolution)
It's pretty clear that waving costs a significant amount of speed, presumably by adding drag. If we need a number, how much drag, here is a real general estimate. Assuming that the highest speed is the terminal velocity for that grade and object (I haven't proven that, but I've been up and down that hill a lot and it is or is close to) then the drag force is equal to the force of gravity. The force of gravity is the same for both roadie and waving, and therefore the ratio of CdxA (Coefficient of drag times area) is the inverse ratio of squared velocities. From the basic drag equation.
In this case, that comes to about 12% greater drag created by waving. So there you have it: drag is increased by 12% when he waves.