If you have spent any time around off-roaders or even web or Facebook groups dedicated to off-roading, you have heard people speaking of airing down. There are MANY benefits to airing down when off-roading. Many people think it is about traction, but that is just one of several benefits.
Face it, we all grew up hearing that having your tire pressure below 30 pounds or so will result in some kind of tire catastrophe, but now you are being told to run considerably lower than 30 pounds of tire pressure. Let's look at that a bit.
To be clear, I am speaking of using non-beadlock wheels. Beadlocks are nice to have, but very few of us have or need them on a daily-driver. Beadlocks are not required for the pressures and low-speed wheeling I am speaking of here. We are talking about using pretty much standard, everyday wheels together with proper off-road-ready tires. Understand, some wheel/tire combinations are better than others. For instance, wide-for-tire wheels are more likely to have the tires come off the bead at lower pressures than slightly thin-for-tire wheels. For example, with a 35x12.50x** tire, a 9" wide wheel may give excellent bead retention at relatively low pressures, but a 10" wide wheel may not offer near the same performance and may require much higher air pressures to maintain bead retention. Generally, I have found that slightly thin (for tire size) wheels do much better than wider ones.
Of course, we are not talking about running these lower pressures on paved roads or at normal on-pavement speeds. This is ONLY about off-pavement driving at slow speeds. Caution and common sense are ALWAYS appropriate. I can only share my experience. YOU have to make the final call on what is the correct pressure for you and your rig.
Lower air pressures, when off-road, aid with traction by creating a larger contact patch of tread on the ground and by allowing the tire to form to the road/rock surface. This additional traction is what most people think of when discussing the benefits of lowering tire air pressures. However, there are others.
The Montana trails I usually wheel on are often covered in a lot of baseball-sized to basketball-sized rocks. At normal tire pressures, these roads are rough (really rough!) and will pretty much beat the crud out of you, your passengers, and your vehicle. A suspension soft enough to smooth these roads out would be useless at on-road speeds. By airing down, we give the suspension some help, by making the tires softer. The aired-down tires absorb a lot of the impacts, vibration, and roughness from the trail, making them a lot more tolerable.
An added benefit of airing down is it can be easier on the environment. The increased traction which comes from airing down lowers the tendency of your tires to spin. Spinning tires tend to dig holes and damage the trails. Additionally, the larger footprint of an aired-down tire spreads the load (weight of our vehicle) out over a greater surface area. This helps to keep us from sinking or digging into the road/trail surface and helps us tread a little more lightly.
What you air down to will depend on your vehicle weight, tire size and design, and the wheel design and size. Smaller tires will require more air pressure than larger tires to remain stable. Air pressures of, for example, 10 PSI, might be fine off-road for a 37" tire, but could be far too low for a 28" tire. Even in the same conditions and on the same vehicle. You may need to play with your pressures to find the best one for your vehicle, tires, wheels, and trail conditions.
I can't tell you what pressure you should run for your particular combination of components. However, I can tell you what I do personally. I am running E-rated, 35"x12.5x17" tires and a 9" wide wheel under my 4-door Wrangler. For summer trails, I am generally going to be at about 14 psi for most trails. If the trail will have some higher speed sections, I may go a few pounds higher for stability. If it is a particularly bumpy, slow driving trail, I might go a couple of pounds lighter, just for the extra comfort.
Always remember that the lower the tire pressure you set, the slower you must go for safety. Quality air-down tools will help make airing down easier. Don't forget a way to air back up. I highly recommend joining a quality off-road club to help you figure out the small details and help you do this and all off-roading safely.
Be careful out there, and always, Wheel Safe!!
Opinion By: Richard Hiltz
A small disclaimer: The graphic is not intended to be an exact representation of what happens with every tire, tire model, tire load rating, or every tire/wheel combination, when aired down. It is just a visual representation for general reference.