While wheelin' offroad, it is common to reduce your tire pressure. With a lower tire pressure, more of the tire is in contact with the ground. This is especially usefull on rocky terrain, where the tire can then flex around the rocks for better traction. Obviously, before getting back on the road, the tires must be reinflated. No problem if you have a Hummer H1 or other truck with Central Tire Inflation System (CTIS). But, most of us are not that fortunate.
Most people have seen, if not used, a portable 12VDC air compressor that plugs into the cigarette lighter socket (CLS). Generally speaking, most of these products are nearly useless for large tire vehicles, such as Hummers H3s. Such compressors typically advertise their ability to inflate rediculously high pressures. Do you know anybody that needs to inflate tires to 350 PSI? What they don't tell you is that they only get that high pressure rating because they push such a rediculously small volume of air per second.
I have, however, come across a product that can take my 285/75R16 tires (33" diameter, 11.22" wide) from 20 PSI to 38 PSI in about 2 minutes per tire. The typical, portable air compressor would have taken about 20 minutes to do the same! For marketing reasons, Q-Industries sells this high volume, low pressure, portable, 12VDC air compressor under two names:
This air compressor is awesome for truck / SUV tires. It is built in a rugged, all-metal chasis and has a built in air pressure gauge. There is an air filter to remove that offroad dust that is undoubtably in the air. The switch is covered with a rubber boot to keep the muck out. It even comes with a 12 foot coil of air hose with a metal quick connect fitting on the pump end, and a screw on fitting on the tire end: none of those cheap plastic lever connectors that never hold the valve stem. Everything packs nicely into the included nylon bag. Because of the electrical current requirements of this compressor, however, it cannot be plugged into the CLS. You'll have to pop the hood and attach it directly to the battery.