Beadlocks have their place but are not required for the pressures and low-speed wheeling I am speaking of here. I am discussing using standard, everyday wheels, and proper off-road capable tires. Some wheel/tire combinations will do better than others, though.
For instance, wide-for-tire wheels are likelier 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 higher air pressures to maintain bead retention. Generally, I have found that slightly thin (for tire size) wheels do much better than wider ones.
We are not recommending 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 the correct off-road pressure for you, the terrain, and your rig.
Lower air pressures, when off-road, aid with traction by creating a larger contact patch of tread on the ground and 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, the real benefits for summer driving include less vibration, less shock from rocks, and a much-improved ride overall.
Of course, the terrain varies greatly from one trail to the next, but the Montana trails I usually wheel on are often covered in baseball-sized to basketball-sized rocks, with larger ones thrown in here and there. 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. However, by airing down, we can help the suspension by making the tires and the resulting ride softer. The aired-down tires absorb a lot of the trail’s impacts, vibration, and roughness, making the ride much more tolerable and even safer.
An added benefit of airing down is it can be easier on the environment. That is why “TreadLightly!” recommends doing it too. The increased traction 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 keep us from sinking or digging into the road/trail surface as much and helps us tread lightly without making ruts. The additional traction means we do not have to spin our wheels, digging into the trails. (or need to do that far less)
What pressure you air down to will depend on your vehicle weight, tire size and design, and wheel design and size. Smaller tires will require more air pressure than larger tires to remain stable and carry the same load. 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’s 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, 35x12.5x17 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 has some higher-speed sections, I may go a few pounds higher for stability and bead security. On the other hand, if it is a particularly bumpy, slow driving trail, I might go a couple of pounds lighter, just for extra comfort and traction.
Always remember; the lower you go, the slower you go.
A quality air-down tool will help make airing down faster and easier. But don’t forget a way to air back up. A portable compressor or CO2 tank is a must for airing back up to normal pressures before driving on paved roads.
I 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!!
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.