This is an old article that compares tires in the 20-25mm range. The bike industry has moved to wider tires and 25 or 28mm tires are now quite common on road bi

This is an old article that compares tires in the 20-25mm range. The bike industry has moved to wider tires and 25 or 28mm tires are now quite common on road bikes, and gravel bikes have much wider tires. I would be the optimum is around 25 or 28 for road bikes on typical roads, especially as aerodynamics become a bigger factor.