Depending on what you're doing, you could probably go almost to 20 psi. I think I was running around 12psi on my 40U, but I rarely checked the tire pressure and sometimes it would get down under 10psi before I checked it. It may have been 3 or 5 psi one time. I never noticed any difference in handling when the pressure was over 10 or under 10. The tires were something x 24 I think. I don't recall the size off the top of my head.