The most basic way to air down your tires is to depress the valve core with a stick or your key, but this takes forever and a day to get a street-pressure tire down to wheeling pressure. If you didn't know it, many tire gauges have a point on the back of the head to allow them to depress the valve core and release air. | 
The next easiest option is to remove the valve core. The valve core screws into your valve stem and can be unscrewed with a simple valve-core removal tool. We also try to install valve caps with a built-in removal tool on all our 4x4s. Be very careful not to drop the valve stem in the dirt when it comes out with all that air pressure behind it. If you do drop it, simply screw the valve cap back on while you're hunting like a maniac for the core, otherwise your tire will quickly go flat and you'll also be hunting for an air tank or compressor. | 
A more high-tech version of the valve-core removal tool is the E-Z Deflator tool from Currie Enterprises. This complete unit screws onto your valve stem and then allows you to remove the valve core within the body of the tool. Next you pull up on the slide valve and air is released. Push the slide valve back down and you can check the internal air pressure with the built-in gauge. Then when you're as low as you want to go, simply screw the valve core back in and go wheeling |
Another angle on airing down your tires uses products that screw onto your valve stem and continuously let air bleed out. The four air deflators from Tera Manufacturing screw together to form a handy key ring, then simply screw them on the valve stem and they depress your core to let the air out. You can check the pressure with the deflators on the stem, and then simply remove them once they reach the desired pressure, as they won't stop themselves. | 
The Staun Products tire deflators come in a handy little leather pouch and can be screwed onto your valve stems at base camp and they will automatically deflate your tires while driving to the trail. The cool part is that they will stop at a preset pressure. Unfortunately, you will need to first lower a tire to your desired pressure by another method so that you can set the Staun units to stop at that pressure. We have found the Staun units very useful, but we also cut out the instructions and keep them with the deflators since they can be tricky if you don't use them often or want to change the pressure setting. However, if you know that you'll always air down to a certain pressure, simply set them to that amount and lock them in--then every time you hit the trail simply screw them on and drive. Remember to remove them before wheeling, and if they get dirty you should clean them as the dirt can influence their precision. | 
Another style of automatic deflators is those made by Trailhead Deflators. These come in a zippered carrying case and they can be preset to a determined pressure by tightening an internal setscrew with an included Allen wrench. Plus the kit comes with laminated instructions and a tire gauge. |
The Trailhead kit comes in two versions, a 5- to 20-psi version for Jeep and 4x4 owners, and a 15- to 40-psi version for motorhomes. In addition, the kit includes a helpful tire-deflation guide that can help a novice wheeler determine a safe tire pressure for many different 15- and 16-inch wheel-and-tire combos. Simply set the guide to your tire size, cross-reference the vehicle's GVW, and you are given a recommended pressure to air down to. | 
The final automatic deflators come from CB Developments via Extreme Outback Products. These are some crazy little units that you can easily adjust from 3 to 13 psi with higher-pressure versions also available. To set the desired pressure, simply press down the plunger and turn to the setting. Then screw the deflators to your valve stem and a low whistling buzzing sound emanates from them till the pressure is reached. Though quick and easy to use, most deflators cannot be used during driving like the Trailhead and Staun versions, but the Extreme Outback is self-cleaning. | 
Other types of air-down tools are those that are installed permanently into the wheel. Advanced Air Systems, the makers of the Powertank CO2 tanks, offers the Monster Deflator Valves that thread into a larger hole than the standard valve stem. This 716-inch hole must be drilled and tapped into your wheels and it is suggested to do it opposite the stock valve. Once the 14-18 pipe thread hole is ready and the new valve is in place, you can simply unscrew the red locking ring and it opens up four 18-inch holes to allow quick airing down. |
Not only do the Monster Valves air down quickly, they can also be aired up quicker since the larger stems allow more airflow, and they come with a big adapter fitting to go from a standard air line to the monster valves. Plus, since your wheel now has two valve stems, you can check the pressure on the stock stem while airing up or down on the monster valve. | 
The Rapid Air Down valve stem must be installed on the wheel prior to mounting the tires. They can be aired up conventionally, but then to air down simply unscrew the big grooved nut and let the air escape through the holes in the body of the valve. Though previously made by Klune-V, these are currently available through Trail Ready and Quadratec. | |