My son discovered the luminous blue bicycle on his fifth Christmas, next to the tree. That cold morning, I led him along living room and dining room circuits as he got the hang of riding on two tires, with a lot of help from training wheels. He was still years away from any possible attempt at the Tour de France, which got under way again this month, and his only performance-enhancing drug was the exuberance of a little boy. Blue-green eyes wide open, he pedaled and pedaled and pedaled.

Late the next summer, I removed the training wheels and set them aside in our garage so Nicholas could learn to ride without them. We rolled the bike up our driveway and into our tree-lined street.

Few cars pass through, but we live on the side of a hill, so turning one way at an intersection means a steep drop and turning another way means a steep climb, too much for a small boy better suited for the level surface of the Champs-Elysees. Also, our street is flat for a short stretch in front of our house, but ends a block away in a dramatic descent. A short distance in the other direction, there's a big dip liable to literally throw off a budding bicyclist.

Within these confines, I showed Nicholas how to balance on the 16-inch wheels, then how to get started.

"Pedal, pedal, pedal," I said, as he started moving.

I supported him with my hands under his arms and showed him how to turn the handlebar before he hit the dip in the road, and how to brake.

Back and forth, back and forth we went, each evening for days on end. He wore his dark-blue helmet, I wore my seldom-used jogging shoes. He struggled to balance, I struggled to run alongside. I didn't have a bike of my own to exercise with, so each lap felt like a mountain stage to me. I thought that maybe I should have kept the training wheels on, because his bike was killing me.

Nicholas managed to ride for about 200 feet in a straight line, but then would sometimes stumble when he tried to turn or brake. Winter came and we put the bike in the garage. I rested.

The next May, I ambitiously drove with Nicholas and his bike down to a winding path at the bottom of the hill. There, he focused hard on pedaling, his eyes narrowed in concentration. Every so often, briefly, without telling him, I stopped propping him up with my hands to see how far he could ride on his own.

"Pedal, pedal, pedal," I said, panting alongside.

The solo distances got longer. One day, I told him that if he rode his bike down the path on his own, from a bridge to a stop sign about 500 feet away, I'd buy him an ice cream from the truck parked nearby.

He did it.

Within a couple of years, he outgrew that bike and got a black, 20-inch model for his eighth birthday. The training wheels went in the trash, and the blue bike went into basement storage for a few months before we decided to sell it. Our neighbors thought about buying it for their son, but it was too small for him, too.

So we took them up on their offer to display it at their yard sale. Nicholas and the neighbor's son set up a lemonade stand near the bike: 50 cents for a cup of lemonade, $50 for the bike.

"But we're flexible," I joked to my neighbor. "We're willing to go as low as $49.99."

Around midmorning, under an azure sky that matched the bicycle, a father came to the yard sale. He took a close look and told his son what a nice bike it was (worth $200 new), although his son seemed more interested in another one with an image of Spiderman on the frame. The father liked Nicholas' so much he didn't try to negotiate with me, other than to request that I lower the seat with a wrench, which I did.

He paid, and I watched him roll the bike up the driveway and into our street. "I'll put some training wheels on it," he reassured his son.

The father laid Nicholas's first bicycle in the trunk of his car to take it away. The pang in my gut felt like a Tour rider had run into me without warning, driving his handlebar into my stomach.

My wife, Beth, and I now have our own bicycles so the three of us can ride together. Because we live on that steep hill, we sometimes strap our bikes to the back of our car and drive to a 2,700-acre estate open to the public, where the landscape of wildflowers and oak is flat.

Once there, Nicholas leads us along the miles of paved and gravel trails as he pedals, pedals, pedals.

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