Dolphins and the Tuesday Night Crits

Dolphins, it turns out, apparently understand instinctively and from the beginning what I am only beginning to grasp.

A new paper by Daniel Weihs (free, reg. req.) calculates that baby dolphins swimming in mom’s slipstream gain between 30 percent and 60 percent of the force required to keep up. Weihs, of the Israel Institute of Technology in Haifa, calculated the hydrodynamics, then looked at aerial photos. He found the dolphin calves swimming in exactly the spot his equations predicted would be the most efficient.

Which brings us to the Tuesday Night Crits, and Aaron Wilson’s explanation that I needed to learn to listen to the wind. The quiet spot, he explained, is the place you wanna be when you’re trying to draft off of another rider.

Bicycle Bill added a Cat 4 race this past Tuesday. Roughly translated, that’s “old farts and beginners,” both categories in which I seem to fit. There were about 25 people who lined up for the start, and instead of being spit out of the back of the pack immediately, I found myself racing with the clump.

The physics of the draft – the thing the dolphins get so instinctively but has taken me a while to master – is profound. Riding at the back of a pace line at 24 miles per hour, you use 27 percent less energy than the guy at the front. Behind a pack of eight, you use 39 percent less energy. Obviously, there’s all kinds of game theory to be understood here, because what’s the point of being in the front? For the dolphin, there’s an obvious mom-child thing going on, but in a bike race who you love and are therefore willing to sacrifice for is a bit more complex.

Whatever. It just seemed like fun Tuesday, sitting in the middle of the pack going close to 30 miles per hour down the tailwinded back stretch, when I saw Aaron itching off to the side like he was going to attack. He did, I tried to go with him and failed, and found myself on the front of the pack, pushing the chase for a lap to reel him back in.

In game-theoretical terms this was a bad idea. I was spending a whole lot of energy hauling the other guys behind me. But blasting around the fourth corner into the home straight at the head of the pack without touching my brakes (it’s a big, wide turn) was about as much fun as I’ve had on two wheels.

I dropped back into the pack after my lap of glory, but we’d managed to bring the break back and we ended up after 8 miles of racing in a bunch sprint. I can’t sprint for shit, but I still was inside the top ten, and our average speed for the race was 24.4 miles per hour, which is the fastest I’ve ever gone on a bike.

I did a couple of laps’ warm down, then lined up for the C race, letting the fast boys go and settling down with a couple of stragglers in a pace line and we still put in a respectable 22 mph for another 20 minutes of racing.

Turns out dolphins also will swim in the stern wave of a small boat for the same reason. Like the cyclists in the peloton, dolphins in the boats’ wake had lower heart rates than those that weren’t drafting. Ducklings are doing it to when they swim behind their mothers, and various flock-flying birds.

Just took me longer to catch on.


  1. Birds do exactly the same thing. This is going to be a lousy explanation, and I take no responsibility for its accuracy…

    When a bird’s wing movement direction changes (ie. going from a downstroke to an upstroke, or vice versa), it loses the circulation going round the wing giving it lift and has to expend energy getting that back again. But this circulation is actually cast behind it in a vortex. When birds are migrating, the following birds use that vortex to recreate their own circulation – again, using less energy at the expense of the leader.

    This is why migrating birds take turns to be at the front.

  2. Now the next thing is: how long to stay in front? When do you get off the front? Does the pack drop you now that you did the work?

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