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A Study of the Use of Lowered Tire Pressure on Forest Product Transportation Vehicles

OCTOBER 27, 1987

The forest service has undertaken a study of the effects of tire pressure on the cost of transporting forest products from national forests. The study stems from preliminary works--done by the U.S. Army and the Forest Service Technology & Development Center, San Dimas, California--that indicated that the use of lowered tire pressure in low speed applications has many more benefits, including:

  • Increased vehicle mobility ( thus fewer miles of road required)
  • Reduced vehicle operating costs (i.e., tire replacement and truck repair expenses, etc.)
  • Reduced driver fatigue and medical complaints
  • Reduced road maintenance requirements
  • Reduced road surfacing requirements

Central Tire Inflation (CTI) systems are mechanical systems that allow a driver to adjust a vehicle's tire pressure while the vehicle is in motion. Using these systems, a truck can be operated with tire pressures appropriate to the speed and strength of the road section being negotiated and the load being carried.

The radial tires in use today can be much more effectively used by adjusting their pressures to match the speed and load of operation. Thus, a radial tire commonly operated at 110 psi on high-speed, paved roads when fully loaded might be operated at pressures as low as 45 psi (again, when loaded)--if speeds do not exceed 25 mph, and as low as 25 psi when empty and speeds are below 35 mph.
A prototype CTI system was used on 10-wheel logging trucks in Alabama and a 10-wheel dump truck in Washington to inflate tires from 45 to 75 psi in 4 to 5 minutes. Inflation from 45 to 100 psi took approximately 13 minutes. Larger air compressors, or reserve air tanks, would improve these times.
Several options are now available to equip trucks with CTI systems. Parts lists and plans are currently being prepared by San Dimas Development and Technology Center for those truck owners who desire the simplest system and have the mechanical ability to install the necessary parts. Hodges Transportation Inc. and AM General have also indicated that they can provide more sophisticated systems. These systems are only available on a special order basis.

Structured tests conducted on test courses where variables can be controlled and quantification of effects can be documented. Also, drawbar pull tests were conducted to document differences in mobility. Operational Field Tests are being conducted to demonstrate the technology and subjectively evaluate the effectiveness of the use of lowered tire pressure using CTI systems under actual field conditions.


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