I've ridden without one. It is hard work. (An Avocet post that broke its clamp and dropped the seat 3 miles from my destination. Seat into my jersey pocket. A lot of standing. Shifting (with DTs) was hard and time consuming. I climbed the 150' hill to the finish in a 42-14 because I didn't know it was coming and there was no way to shift once I started up!)

Ben