Some of us wonder why, when, etc. we "air down" our tires when we go 4 wheeling. Basically we air down to get better traction and to provide a more comfortable ride. The following information is from the web site for Oasis Off Road Mfg, http://www.oasis-off-road.com. This web page has a nice table that provides a Tire Deflation Guide for quite a few tire sizes and vehicle weights. Oasis sells automatic tire deflators that can be screwed on to your tire valve stems and will deflate yours tires to a pre-set pressure. Staun also makes deflators that can be screwed on to your tire valve stems and can be found at; http://www.stauntyredeflators.com

In the February 1997 issue of Peterson's 4-WHEEL AND OFF-ROAD magazine the subject of "How to choose AIR pressure" is discussed by Feature Editor Rick P'ew'e. We suggest that you read this article. Portions of the article specifically related to "airing down" are passed along for your information:

• Learning to drive on soft tires takes practice and patience, Fundamentals include no quick turns and no bashing hard surfaces. High-speed sand and mud turns will surely debead a too low tire. Always air up before hitting the highway.
• Basically, the faster you go the more air you need, On smooth surfaces such as granite or sand, lower pressure aids in flotation and traction while the protection of high pressure is not needed.
• Over inflated tires on the trail offer little traction and no shock-load absorption. Letting out a little air will often allow the tires to pull the rig easily over the top without all the fuss of broken components,
• A tire with lower pressure is more puncture proof in low speed situations.
• Proper tire pressure is and always will be what's right for you and your situation, not what someone else is running - and especially not the figure listed on the doorjamb.
• The proper tire pressure for individual circumstances depends on the size and load rating of the tire, the stiffness of it's construction, the rim width verses. tire width, the gross weight to the vehicle, the type of terrain, the speed of the vehicle, and the drivers expertise,
• If you can't air back up before hitting the highway, air down only to a safe pressure to make it back home. Or get a tire pump / air compressor.

Remember that it's the volume of air in the tire that supports the weight of the rig, not the pressure. A large tire has more volume than a small one, which is why more air volume needs to be crammed into a little donut to support the same weight as a big tire and hence different weight ratings. Generally the lighter the vehicle and the bigger the tires, the less pressure you can run.

Harry Lewellyn from Ecological 4 Wheeling adventures recommends measuring the height of your rim from the ground at full pressure, then deflating until the height measures 75% that of full pressure. eg: If the bottom of your rim is 10" off the ground at full pressure, air down until it is 7.5" off the ground.

General Rules:

1) Increase pressure approximately 3 psi for each 10 mph over 20 mph, until normal highway pressures are reached. For example: A 3000 lb. vehicle with 31x10.50R15 tires traveling at 40 mph should have about 15 psi in the tires (9 + 3 + 3 = 15).

2) Decrease pressure by approximately * for extremely soft snow. The exception to this is a 33x9.50R15 tire, which usually benefits from an increase in pressure.

3) Decrease pressure approximately 1 psi for every two inches tire diameter is increased beyond this chart, assuming a corresponding increase in width of the tire.

Remember, these are suggestions. Set your tire pressure where you feel comfortable driving when off road.

Use extreme caution when driving with partially deflated tires (any pressure other than the manufacturer's recommended pressure) whether on or off pavement. If you are traveling too fast while turning with partially deflated tires you may pull a tire's seal off of it's wheel. You will instantly lose all the air in that tire, which may result in your vehicle rolling over or going out of control, causing death, bodily injury and/or property damage. The dangers of traveling with partially deflated tires are NOT LIMITED TO THIS EXAMPLE !

Revised: 3/9/04