Man, when I was a kid we learned to ride on a fixed gear. It had solid rubber tires and we called it the "schkreepa bike" because that was the noise it made when you rode it. "Schkreepa...schkreepa...schkreepa" I wish I knew what happened to it, because I've been contemplating the same thing for my five year old. He recently made the transition from tricycle to mini-bmx with training wheels.