Run mid-to-high teens PSI for sand, 18-22 PSI for rock, and mid-to-high teens for mud, all on standard wheels. Never drop below 15 PSI without beadlock wheels, which let sand pressures fall into the single digits and rock pressures down to 14-16 PSI.
Airing down is the single highest-value thing you can do before a trail, and it costs nothing. Dropping pressure lengthens the tire's contact patch, which spreads your weight over more ground, soaks up impacts, and lets the tread conform to terrain instead of skating over it. But there's a hard limit: drop too low without the right wheels and the tire can unseat from the rim (a de-bead), usually at the worst possible moment, leaning on a side-slope. This guide covers what each surface wants and where the floor is.
How low is “aired down”
There's no single number (it depends on tire size, load range, and how heavy your rig is), but the goal is the same everywhere: a visibly longer, flatter footprint without the sidewall bulging so far it risks the bead. A heavier truck on stiff Load Range E tires needs to drop further from street pressure to get the same patch growth as a lighter rig on softer tires. That's why a good calculator starts from your door-jamb placard pressure, which already reflects the vehicle's weight and the tire's load range, not a blanket “run 18 PSI.”
By surface
Sand
Sand rewards the largest footprint of any surface: you're trying to float on top, not dig in. This is where you go lowest. Most rigs run in the mid-to-high teens on Load Range E tires; with beadlock wheels you can safely drop into the single digits. The calculator's bead-retention floor is 15 PSI on standard wheels and 8 PSI on beadlocks. Without beadlocks, hold at or above 15 PSI (more on that below). Air down before you hit the soft stuff, not after you're stuck, and keep it under about 15 mph once you're in the teens.
Rock
Rock crawling is about conformity and sidewall protection, not float. You want the tire to wrap around edges for grip, but enough pressure to resist a pinch flat or a de-bead on a sharp ledge. Most experienced crawlers settle around 18–22 PSI without beadlocks, and 14–16 PSI with them. Published load and inflation tables for LT tires start at 35 PSI, so nothing in this range carries a rated load: these are crawling pressures for crawling speed, a few miles an hour, not for the graded road back out.
Mud
Mud is a compromise: some airing down helps the tread open up and find the firmer base below, but go too low and you lose the ability to self-clean and you risk spinning a tire off the bead under torque. A moderate drop (think mid-to-high teens on standard wheels, staying at or above the 15 PSI floor) is usually right. Momentum and tread pattern matter more here than the last 2 PSI, and momentum means a steady roll under about 15 mph, not speed.
Gravel and dirt roads
For maintained forest roads you don't need to go nearly as low: a modest drop from street pressure smooths the washboard and saves your fillings without much de-bead risk. This is the most forgiving surface, and the one place a normal forest-road speed is still fine, because the drop is small; anything in the teens is a trail pressure and gets a trail speed.
Slow down when you air down
Every pressure above comes with a speed. A tire at trail pressure flexes more, builds heat faster, and gives up steering response, and a hard side-load at speed is what rolls a bead off the rim. Below about 20 PSI keep it under roughly 15 mph; at single-digit beadlock pressures, treat it as walking pace. The dash TPMS warning is no help here: it trips at a fixed threshold below placard, about 25 percent under on US-market vehicles, and stays lit the whole time you're aired down. Set and check pressure with a gauge you trust, and air every corner to the same number.
The 15 PSI de-bead floor
Here's the rule that keeps you out of trouble: without beadlock wheels, don't run below about 15 PSI. A standard wheel holds the tire bead in place with air pressure alone; drop too low and a hard side-load can break the seal and roll the tire off the rim. The 15 PSI figure is a conservative rule of thumb, not a tire-maker spec: the pressure a bead lets go at depends on the wheel, the tire, the side-load and the speed, which is why the floor carries margin and why speed matters as much as pressure. Beadlock wheels mechanically clamp the bead, which is exactly why they let you run single digits in sand. Our calculator enforces this: when a terrain's share of your placard pressure lands below the floor, it raises the result to 15 PSI on standard wheels (8 PSI on beadlocks) and says so in the verdict. It will never quietly hand you a dangerous number.
Re-inflate before pavement
Aired-down tires on the highway build heat fast, wear the shoulders, and can fail. Always air back up to your door-jamb placard pressure before you get back on the road. Carry a compressor sized for your tires; a small plug-in portable can take several minutes per tire on 33s, which gets old on a four-tire reset.
Bottom line
Start from the surface guidance above, then dial it in for your actual rig with the Airing Down Calculator. Lower for sand, moderate for rock and mud, never below 15 PSI unless you're on beadlocks, and slow down while you're low. Air down before the trail, air up before the highway.