What tire width should I run on my endurance bike?

For most riders on typical roads, 28mm tires at around 4.5–5.5 bar (65–80 psi) provide an excellent balance of speed, comfort, and grip. If your roads are particularly rough or you ride long distances, 30–32mm tires at 3.5–4.5 bar (50–65 psi) will be faster and more comfortable. Contrary to old assumptions, wider tires at lower pressures are faster on real roads because they absorb vibration rather than bouncing over it. Start at 28mm and experiment — you will likely find that wider is better.