Bicycling put together a package called “The 50 Greatest Things About Cycling,” and one of my suggestions was “speed.” I’d sort of figured that single word would suffice, but when we decided I should do more on it — I’m the go-to guy for overthought, voicey essays — I was surprised by how much I had to say, and then as I got near the end, how little.

Eleven miles per hour: Flying. It was one of those days so windy it becomes a personal legend. After mostly tacking against 15-40 mph westerlies for 50 miles, my friend and I pointed bars straight into the screamer and crawled forward at 5-7 mph. When the road dipped below a fallow cornfield or cut between cliffs striated with jasper, our pace would spring to an 11-mph that, after two hours of single-digits, felt as fast as I’ve ever pedaled a bike. I might have been doing 37 in the Thursday night crit.

Speed isn’t a number. It’s a sensation. And it’s a sensation that, as the wind reminded me and as any bar-room physicist can tell you, is relative.

On the simplest level, we experience speed against each ride’s context. The sole 50-mph downhill on the local loop feels insane. Corkscrew your way down something like Mt. Ventoux’s 14 miles and you find yourself slowing to 50 so you’ll be safe in corners.

Speed also depends on the speed of the observer, according to the cyclist Albert Einstein. When you’re riding, because you and your top tube are traveling the same speed, it isn’t moving relative to you. To the cyclist you’re passing, it might be moving 10 mph. To the kid standing on the sidewalk, it might be moving 30 mph. And because speed is nothing but distance over time, whenever you turn a pedal in pursuit of one more mph, you blow the stability of the world as we know it into the realm of relativity. It’s like this: You cruise down a one-mile road at 12 mph, timing yourself on a computer while a friend standing still on the curb times you as well. (Assume the impossible, that you both start and stop your timers at exactly the same instant.) To your friend, you completed the mile in 300 seconds. To you: 299.9999999999952 seconds.

I don’t understand the science. And I know those blips are impossible to measure or feel. But I believe that cyclists know speed changes everything. It changes an afternoon, it changes how our kids look at us, it changes the taste of water in a plastic bottle, it changes gelatinous carbs into fire. It changes us. Add up all those 0.0000000000048 seconds stolen in the saddle and you get something beyond blurry eyes and town-line victory flourishes and savory danger and frustrated dogs. Like I said, I don’t know what you get, or why, but I know this: Shaking the fabric of the universe itself makes me grin like a fool.

Originally published in Bicycling magazine, March, 2004