Part two, the class at the Overland Expo was great.
They basically parked two 4WD vehicles in front of sand. One a small Toyota pickup, the other an SUV. Two different tread designs. Drove each across the sand at stock pressure.
The pickup started struggling in 2WD and did the wheel hop/axle wrap thing a bit, I think the SUV made it without any real spinning or hopping. I think they put the pickup into 4 and drove it the rat of the way.
We then inspected the tracks, measured width, and also marked the LENGTH of tire patch in the sand.
They raked the sand smooth, leaving the length and width marks, then aired down each vehicle....but also set the right side of each at a different pressure than the left side. So we covered the spectrum of 5 different reduced pressures. They marked the length and width of each.
He talked about a lot of things from tread design and sand type (which varies a lot!). The biggest things I remember:
The big difference airing down makes is in LENGTH not in width (so think about that with a dually 16" tire)! The length will gain a LOT and make a LOT of difference in behavior and traction, but the width changes much much less. So, you can probably make a big difference by airing down a dually, before the tires ever touch, assuming you have at least some space to begin with.
It always depends on the specifics of the situation and you have to simply go by trial and error as you learn your vehicle. Don't be afraid to try! Have a refill means! Try the sand test with a take and measure how the tire footprint changes as you lower.
