Originally Posted by
msu2001la
Every tire, rider and course is a bit different, so it's something you should experiment with, but generally speaking your teammates are probably correct in saying that 30-35psi will be faster than 40+, assuming you can run that low of a pressure without pinch flatting. Lower psi will smooth out the ride and roll faster over bumps, give you more traction in wet/mud, but it also comes at a greater chance of pinch flatting. This is the basic risk/reward factor in CX tire pressure.
Generally you want to run the lowest psi possible. Clinchers with inner-tubes pinch flat much easier than tubulars, and they also have stiffer sidewalls so the benefits of running them at ultra-low pressures more diminished and also come with higher risks. Keep going down this rabbit hole and you'll quickly learn why tubulars are so popular for CX.
I weigh around 165lbs and 35psi is about the minimum I feel comfortable running my 33mm clinchers, but I'll run as low as mid 20's on my 33mm tubulars, and the newer Donnely tubulars don't even have an inner-tube to pinch (it's a tubeless casing), so I would imagine they can be run extremely low and still not flat.
I'm 170 and have gone down to 40psi on my ghetto tubeless set up. My kid is 130 and run his in the low 30s. I was afraid he would burp them on off-camber stuff, but he was fine.
And FWIW, Cody Kaiser advises going high pressure in muddy conditions to help the tire dig down to more solid ground. He says if you go low pressure in mud it will tend to float and skate over the mud. YMMV.