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AGF 4x4 Resources · Field guide

Tires & air

How low to air down, how old your tires really are, and what to do with a flat a long way from a tire shop.

A red Land Cruiser crawling over loose rock on a high mountain trail
Rocks near Cooke City, 2026. This is where airing down earns its keep.

Air-down planner

A starting point, not a final number. Start high, then drop 2 to 3 psi at a time until the rig stops spinning or bouncing.

Ranges are common practice for 33 to 35 inch all-terrain tires (OK4WD). Without beadlocks this page never goes below 15 psi, the floor WARN gives for regular wheels. Tall sidewalls and LT load ranges behave differently, so watch the tire, not just the gauge.

Driving aired down

  • Slow down. Low pressure plus speed heats the tire and can wreck it or blow it out.
  • No sharp, fast turns. Side load is what pulls a bead off the rim. Ram's owner's manual warns low pressure "may cause tire unseating with total loss of air pressure."
  • Air up before pavement. Every manufacturer source says the same thing. Carry a compressor and a gauge, or don't air down.
  • Check cold pressure at home against the door-sticker number, not the number on the sidewall.

How old are your tires?

Find the DOT code on the sidewall. The last four digits are the week and year it was made: 0322 means week 3 of 2022.

Some vehicle and tire makers say to replace tires 6 to 10 years old no matter how much tread is left (NHTSA). Old rubber cracks, and a cracked sidewall on a rock trail is how a day ends early.

Flat on the trail

  • Sidewall or shoulder damage: put the spare on. Those can't be repaired properly, even in a shop.
  • Small hole in the tread: a string plug from your kit can get you home. Air it up, check it again in a few miles, and keep speeds sane.
  • Then get it fixed right. The tire industry standard (USTMA) is a plug-and-patch repair from inside the tire, after it's off the rim and inspected: tread area only, a hole no bigger than 1/4 inch, and never overlapping another repair. A plug alone isn't a proper repair.
  • Lost a bead? Clean the bead and rim, get the tire back over the rim lip, and use a ratchet strap around the tread to push the beads out while you air it up fast. Stand clear while it seats.

A full-size spare that matches your other tires is the real fix. Know where your jack points and lug key are before you need them.

What to carry

  • A good gauge (the one on the compressor lies) and deflators or a valve-core tool
  • A compressor that can refill all four tires in a sane amount of time
  • String plug kit, spare valve cores, valve caps
  • Full-size spare, jack that lifts your lifted rig, a board for soft ground, lug wrench and lock key

Running bigger tires? Check speedometer error and gearing in the 4x4 calculators →

Sources