I noticed that airing down really helped me preform much better on the trail, but i only went down to about 18 psi in my 31" 10.50s.

what i'm wondering is how low is too low. and will going that low help any?
what should i run pressure wise to get the best traction?
does the best PSI for your rig change because of tire size or weight?

 

I air'd down to 12 psi when I was at pismo beach the other day. a friend of mine went to 10 in his 31x10.50s i think. but this is in sand...

 

What size rim are you running? That can make a big difference
I run 10 in the rocks on my 35x12.5 with an 8 inch rim

 

Excellent article below:
- http://4x4now.com/sfjun96.htm

I find Harry's "sand pressure" (75% sidewall height) is about the lowest you want to go like in deep sand or snow for that given wheel/tire combo mounted on your vehicle. Then work between that and your normal pressure as terrain dictates. Higher pressures for higher speed or harder terrain and lower when you are going slower and need more traction.

I usually start at 20 psi for washboard gravel and faster dirt roads, 15 for most rocky trails then lower as needed. I've run my 33x9.50 or 10.50 tires as low as 6psi in snow and I used to drop my old 33x15.50 Swampers into the 1-2psi range in snow and sand.