Death Valley question

Started Nov 6, 2008 | Discussions thread
mmullen
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Re: I don't think it would be a fun drive in a car, just long and tedious.
In reply to David I Hale, Nov 25, 2008

David I Hale wrote:

Picture a balloon.. If you fully inflate it, it's very easy to pop
it.. if it's only halfway inflated, it takes much more effort to pop
it as the surface will give more.

A passenger tire is very different from a balloon.

There is no "correct" pressure for off-road driving, it really depends upon the specific tires, rims, terrain and conditions. This discussion was regarding the wisdom of taking a passenger vehicle into a remote area. True, off-road tires can be aired down and with the right tires and rim locks can go to 5 psi or even below at very slow speeds for rock climbing, etc. Off road tires have tougher sidewalls and should be mounted on rims that have good support for the tire bead.

Passenger radials have soft sidewalls because they are designed to flex. That is why radials sidewalls bulges outward, even with the correct pressure. This bulge makes the fragile sidewall of a passenger radial susceptible to cuts from sharp rocks and lowering the pressure too much increases the vunerability.

Also, wheel rims on some newer SUV's and cars have poor rim bead support and should not be aired down because it is the tire pressure that keeps the tire bead of a tubeless tire seated on the rim. The softer the sidewall of the tire and the less support the wheel rim offers, the more true this is. The last thing you want is a flat in the middle of no where.

Yes, if you have all terrain tires and rims and the means to re-inflate the tires before driving at speeds above 30 mph, by all means, air them down. The optimum amount will be determined by the specific tires and existing conditions. It also depends upon what your goals are. The pressure that provides the optimum traction for climbing over steep technical rocks will not be the pressure that provides the most protection from flats and broken beads.

Most light passenger tires and rims can go to 25 psi without serious issue as long as speeds are kept down, however, I recommended 30 psi because the tires will almost always be warm when the tires are aired down (due to driving). Warm pressures are about 5 psi higher than cold pressures so never airing below 30 psi insures the tires will always have at least 25 psi cold. And at these pressures you will need to air them up before extended driving at higher speed to avoid increased risk of blowout.

BTW, I have 29 years experience driving off-road in Canada, Mexico and the US with primarily four wheel drives but also considerable experience using less than optimum equipment to get to wild and scenic places in vehicles including VW Rabbit and bug, Subaru wagon and Volvo sedan. What works well with heavy-duty off-road tires and wheels cannot always be safely applied to modern light passenger equipment.

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Mike Mullen

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