Once you start venturing away from the main roads, it won’t take long for you to get stuck your first time. When this happens, you will start looking for ways to keep it from happening. One of the first and most effective ways to improve traction is to air down. Here we will discuss why it is done, when to do it, how to do it, and how much air to use. It is important that you realize that this will serve as a guide only. Your actual results may vary. It is also critical to note that once you intend to do speeds in excess of 25 mph, you need to bring the air pressure in your tires back up to normal pressure to be safe.
Why air down?
Airing down does two basic things to help us maintain traction. First, it allows for a longer and wider footprint. This is important because the more rubber you keep in contact with the terrain, the more traction you will have. In many cases, you can increase your contact with the ground over 200% by airing down. This will increase your overall traction as much 800% assuming you have 4 tires on the ground.
The second thing airing down does for us is that it allows the tire to conform to uneven surfaces. If you imagine your foot for a moment in heavy boots standing on a log, you can see that only a very small portion of your foot is actually in contact with the log at any time. Remove the boot and stand on the log with your bare foot, and your foot can bend and conform to the log giving you a much more firm grip. Tires need to do this when trying to get grip over rocks, gravel, sticks, etc. The difference is truly amazing. An added side benefit is that reducing the pressure in your tires softens the ride tremendously while off-road.
When should I do it?
Airing down is usually done at the trailhead. If you will be traveling over 25 miles per hour, I don't recommend it, but when the going gets tough, and things slow down, taking the air out of your tires would be prudent.
A concern here is airing down stock tires. The stock tires have a VERY thin sidewall. This means that when you air them down, the sidewalls have a better chance of making contact with the nasty things on the ground like rocks and sticks. Be careful.
How do I take out the air?
This really is as simple as it seems and there are any number of ways. You can use almost anything to press down the valve on your tire stem and let the air out. However doing this will necessitate you using a good tire pressure gauge (which you should own anyway!) so that you don't over shoot the target. There are small tools that screw onto the valve to remove air quickly and easily, and I recommend buying these. At the top end of that chain, Oasis-Offroad offers a set of screw on deflators that you can actually calibrate to STOP deflating at a pressure you decide. This means that you can literally screw them on at the trailhead, and in a couple of minutes, your tires will be at the proper off-road pressure! For the price of about $55. If you go off-road a lot you WILL understand what a bargain this is.
How much air should I use?
This is an issue of MUCH debate. Land Rover recommends that the stock tires should not be aired down below 16 psi in the front and 25 psi in the rear. In truth, with a standard load in the rear, this is probably good advice. If you take out too much air, you run the risk of rolling the tire right off the bead. This is very likely with the stock tires since they really don't grip the rim all that well to begin with. With off-road tires in the larger sizes, you can go lower. I have had my 215/85r16 tires at 12 psi without trouble but I don't recommend going that low. I will defer to a chart provided by Oasis-Offroad. They have taken the time to determine optimum tire pressures for off-roading for a range of different sized tires on vehicles of different weight. While the chart is by no means comprehensive, it does offer good insight into what you should be looking at. Please note that Oasis maintains no responsibilty for the accuracy of this chart and bears no responsibility if you have a loss.
So you can see that this is really not a complicated affair, but one that every off-roader should pursue if you want maximum traction off the road. One thing of note. If you plan on airing down off the road, be SURE you have a way to get air back into your tires when you are done.