Understanding how to properly regulate your vehicles tire pressure will enhance your 4x4's tire performance on and off the road.
Remember, it’s really the air inside the tire that supports the vehicle, not the tire.
Tire inflation will affect…
- Traction & braking
- Load capacity
- Gas mileage
- Susceptibility to hydroplaning
- Tire wear and failure
- Vehicle handling & stability
- Ground clearance
- Steering response
Tire Inflation Basics
For discussion purposes, let’s assume that 30 psi is the cold tire pressure recommended by the vehicle manufacturer at normal operating weight.
The tire is assumed to be cold if it has not been driven for several hours, out of direct sunlight and the ambient temperature surrounding the tire is about 60 degrees F at sea level.
Please note that when running radical off road tires, the vehicle manufacturer’s recommended inflation pressure may not apply, due to your tires maximum pressure limitations.
Also take into account other common sense tire inflation basics, such as vehicle weight, tire type and terrain considerations.
What is the Best Tire Inflation?
There is no simple answer to this question. I learned the hard way when I first began buying All-Terrain tires and wide rims back in the 1980's. My stock 29 inch tires were 35 psi max and my new 31 inch BFG AT’s were 50 psi max.
I always ran my stock tires at 32 lbs lightly loaded and 35 lbs heavy so I figured I should run my new 50 psi AT's at 45 lbs light and 50 lbs heavy. Wrong… I rapidly wore down the centers of my new tires.
Through trial and error, I found that 32 psi turned out to be the magic number... lightly loaded and 45 psi heavy. You can always experiment to find the right combination.
Determining Best Tire Inflation for Your Vehicle
First inflate your tires to recommended pressure, then place a chalk line across the tire tread. Drive ahead about 10 feet and see where the line first wears off.
Too much air pressure and the center wears first, too little and the outer edges wear first. Keep experimenting until the chalk wear is even all the way across. The result is your best all around tire pressure.
Check your air pressures often with a good tire gauge. Visual checks don’t work. Keep in mind a tire rated at 30 psi will look about the same at both 20 and 40 psi. It is very important to keep all four tires at the same air pressure for better handling and safety.
Temperature influence on tire pressure
Your tire pressure will normally fluctuate 1 psi higher for every 10 degrees rise in temperature and 1 psi lower for every 10 degrees drop in temperature.
Temperature fluctuation examples
1. Driving down the highway heats the tires, so under normal conditions expect the 30 psi tire to gain 4-5 psi in the first half hour and then stabilize.
You stop to check the air pressure (it now shows 34-35 psi, which it should). If you adjust back to 30 psi, you actually have only 25-26 psi once it cools down.
2. You drive hours on the highway to an off road destination. Upon arrival you air down your tires to 15 psi and go four wheeling.
You camp out that night and set out early for more 4x4 fun. Depending on overnight temperatures, your tire pressure could now be below 10 psi. Risky, unless you have beadlock’s.
The point is… know when to check your tire pressure and how to interpret correct inflation with changes in temperature.
Other Influences on Tire Pressure
Normal tire air loss, seasonal change in ambient temperature and punctures, all effect tire pressures.
1. Airing Down
4x4 enthusiasts like to air down their tires for more traction and a softer off road ride. I remember when it was common to air down tires on 2 wheel drive vehicles to get unstuck! Was that the beginning of airing down?
For the most part, airing down isn’t necessary for most off-roaders. Your recommended highway inflation pressures will perform nicely, both on the pavement and during off road excursions. All without having to fiddle with tire pressure.
On the upside… what you can expect from airing down is a smoother off road ride, and better traction, mostly on rocks, sand and snow.
On the downside… you have to go though the trouble of airing down and then airing up again. You have to buy some sort of portable air compressor or storage tank, you will lose ground clearance and you run the risk damaging your tires and rims.
How low can I air down?
Rigs with beadlock wheels and good tires usually run from 4-15 psi, sometimes going down as low as “0” psi for short periods of time.
Rigs with conventional wheels have to experiment to see what works best on different terrain. A good rule of thumb is… don’t air down below 15 psi without beadlocks.
Some wheels found on newer SUVs and pickups should not air down at all, due to poor rim bead support. So it’s a good idea to know your wheels before airing down.
Air down accessories
- Regular and low pressure tire gauge.
- Valve core remover or depressor.
Off Road Air Sources
You have several choices for an off road air source:
1. Engine driven compressor mounted on your engine.
2. Compressed air or CO2 in portable storage tank(s).
3. 12V portable air compressor.
4. Hand or foot pump.
Here are a few handy tire pressure accessories:
1. G.H. Meiser & Co. Makes several neat tire accessories for 4×4 off road use such as the EZ-Deflator and ACCU-GAGE
2. Sun Performance Products Is the provider of the QuickAir onboard and portable air compressors. They also supply the QuickAir Deflator and Low Pressure Air Gauge.
3. Advanced Air Systems, Inc.