Suspension losses cause a significant resistance when riding your bike. We knew this from our testing, but it was illustrated in a powerful way during a 300 km brevet a few years ago.
My friend Ryan and I rode in a group of about 10 randonneurs. Everybody was taking equal pulls at the front, until we got to a particularly rough road. It wasn’t chipseal, but an old road surface where the asphalt had eroded away over time between the aggregate. It was hard for us not to miss the fact that the rough road caused more resistance. Even though the gradient hadn’t changed, you could hear one rider after another shift to an easier gear. The pulls at the front became shorter as riders were trying to maintain the group’s speed.
One rider curiously seemed unaffected by the surface change. Ryan was riding his randonneur bike with 650B x 42 mm Grand Bois Hetre tires. He was in the same gear as before, and his pulls at the front remained at the same speed as they had been on the smooth pavement. You could hear the other riders grunting and breathing harder when Ryan got to the front, and he isn’t usually a rider who forces the pace. Fortunately for the rest of us, after a few miles, the rough pavement ended. Ryan was back to normal, since his pulls now were at the same speed as everybody else’s.
I was riding Grand Bois 700C x 32 mm tires during that brevet, which most cyclists would consider ample for paved rides. Yet the difference in speed to the 42 mm tires was remarkable. The difference in comfort was no less remarkable. At the finish, I told Ryan: “That section of rough pavement along the Skagit River was really punishing.” He looked at me a bit incredulously and replied: “I never noticed it.”
Further reading: A blog post explaining suspension losses, how we measured them, and approaches to minimize them.