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DESERT TRAVEL A Lesson in Desert Safety By Bruce F. Barber
He had never really given it a thought. That is, he knew his tires had good tread on them but had never thought much about their width. Now, however, having buried his dune buggy in soft sand, he began to wonder why and a comment he'd once heard came to mind. That was, "You'll be sorry you decided on narrow tires." Narrow? At eight and a half inches in width they didn't look narrow but, suddenly, he was buried to the hubs in sand and he began to wonder... This man, who is one of a hundred I've known over the years, had laid a trap for himself. Like most of us, he knew too much for his own good. That is, he thought he knew enough about tires to write a book but he had no appreciable desert experience. And, among the many (desert-related) lessons to be learned is one called SAND, one of the most difficult mediums to drive in (or on). Other, related, lessons include Wheel Size, Taxable Horsepower, and Tire Inflation. The key to driving on sand is related to the coefficient of traction (a mathematical formula none but a few can work). Formula or not, providing the proper traction for trouble-free driving in sand requires an optimum amount of tire surface being in contact with it. The usual method involves the use of wider-than-normal tires beginning with the10.5-inch tire (a full two inches wider than the tires used by the man mentioned above). Whereas the 10.5-inch tire is a starting point, the actual width depends entirely on vehicle type and weight although a given vehicle's fenders may limit allowable tire width. Most of us running the San Felipe Desert (men and women driving Sandrails, Dune Buggies and Baja Bugs) use 11.5-inch driving tires and 8.5-inch steering tires mounted on matching rims. You see, the owners of these Volkswagen engine-powered vehicles are also concerned about tire assembly weight and the (engine) horsepower required to rotate their tires. Consequently, most of our 11.5s are mounted on 9-inch wide rims while our steering tires are mounted on 7-inch rims. Having said what we have above, it is essential to point out the fallacy of tires in use on the "Jeep" style vehicles (Jeeps, Suzukis, Geos and etc.) as well as most other 4-wheel drives including pickup trucks and S.U.V.s. Most of these tires range in width between 7.5 and 9.5 inches. And, although the 4-wheel drive vehicles have an edge over other vehicles, the smaller tires mentioned (and sidewall construction) remain a problem to be reckoned with. Wider tires, including the 12.5 to 14.5 paddlewheel style, are not required in the desert and a) owing to tread and sidewall construction, are more susceptible to puncture; b) in combination with the requisite wheels, are so heavy they can sap needed horsepower in soft sand terrain. Whereas tire pressure controls the amount of available surface in direct contact with the roadway (whatever it may be), sidewall construction can permit or prevent a given tire from "ballooning" to apply more surface to the roadway. Ballooning is a condition created by reducing tire pressure. Most of us tend to think of "highway pressures" being in the vicinity of 32 pounds per square inch (although pickup and other truck tires can run to 45 psi). When thinking about pressures to use with desert vehicles-vehicles to be used on pavement, dirt and sandy surfaces-one has to open his or her mind to the reality of traction. Consequently, we set aside our "highway pressure" knowledge and begin to think in terms of traction in desert regions. We begin by inflating 10.5- or 11-5-inch tires to twenty pounds per square inch and run at that pressure for all surfaces until we anticipate soft sand. At that point, regardless of the type of sand (because there are many types of sand, we herein identify only volcanic, seafloor and granitic), we will reduce tire air pressure to 11 pounds per square inch (a pressure that works well in almost all sands) and proceed with caution. NOTES: a. Admitting lower pressures are used on special occasion(s), it must be recognized there is a pressure one does not go below for fear of losing a tire's grip on its wheel. Therefore, reducing a tire's pressure below 11psi is not recommended. b. Whereas many men and women are reluctant to reduce tire pressure for fear of running soft tires on hard pavement, the most important consideration when a vehicle is stuck in sand is getting it on that hard surface first and worrying about soft tires later! Besides, desert safety demands every vehicle be equipped with a tire pump!
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