Anything in the low to upper 20s is common. There is no single tire pressure that's going to work for everyone. Terrain, conditions, bike type, bike setup, rider weight, riding style, and tire size are some of the variables to consider. I raced a lot of XC back in the day so I always wanted to run as low a pressure as possible. Now that I only ride trail and big, pedally backcountry rides, I run higher pressures (24 f / 27 r) because I want support and feedback from my tires. In the wet season I run a bit...