I know we can get crazy with how you ride, how much you weight, and a million other specifics. My question is rather general in nature and asks what kinds of pressure do you typically run for certain courses.
Lets assume that if the course has a mix of condidtions (some dry, some wet sections) you run Xpsi...
If it's a dry/fast course, do you run higher or lower pressure than you typically would?
If it's a soft/wet course, do you run lower or higher pressure than you typically would?
Drier higher. Advice that rhymes is always right.
In all seriousness you'll go a bit higher for dry otherwise you feel like you're riding a flat and it's slower. In the mud you want all the surface area you can get, so lower pressure.
I think the one thing to remember, is that at least here in Norcal, is that drier does not always mean less bumpy. In fact, sometimes the dirt is so dry it's like rock hard concrete, but not smooth at all. On a bumpy course - you'd definitely want to go lower assuming you can avoid pinch flats. Lower pressure helps with traction, but as Oliver said, tread can go a long ways there too. Pressure should more often be dictated by how bumpy the course is - as that will make a huge difference in speed, even if traction is already plentiful.
You didn't say if you're running clinchers or not, that will definitely be a factor. The type of tube is too (see our CXM Labs snake bite / pinch flat test in Issue 9 of the print mag). You can also of course pinch tubulars (Tufos are much harder to pinch since they don't have tubes) - a good tubeless clincher setup could be the way to go too. FWIW, I ride high 20s psi in clinchers, mid 20's tubeless/tubular and weigh 160 pounds. Very few courses and course conditions have me at higher pressures.
Fast courses often do mean higher pressure, if it's smooth, or if it has high-speed bumps as the higher speeds mean it's easier to pinch if you do hit a bump.
Soft/wet does typically allow/require lower pressure because you want traction and you are typically going slower.
There's a great article in Issue 13 on all of this tire pressure stuff ("Pressure Refresher") should really get your hands on - as well as the tire pressure time trials (Issue 3, Issue 6 "Under Pressure Pt 1, Pt 2) we did in past back copies. All available here (and most avail via digital). In general, with the exception of cornering handling and flat risk, our time trials show that lower is better even just on moderately bumpy grass. Take a look at the two rounds of testing we did. That opened a lot of people's eyes to the quantifiable benefits of low pressure beyond traction.
Actually issue 13 just arrived. Thanks for the info, just the kind of thoughts I was looking for.
This year I will be on a tubular set with Grifo's with a set of clinchers in the pit that I can swap out tires if need be.