The paper treats the subject of ability from the point of view of its relation to the present trend in motor-truck design, setting forth some of the fundamental considerations involved. An ability formula when applied to automotive vehicles is to determine a “factor of experience” from which engine sizes and gear ratios can be calculated. While passenger-car performance is measured in terms of speed and acceleration, the latter are not the most important considerations in motor trucks, the speed of which is limited by the use of a governor. Wind resistance also is negligible at truck speeds. Practically the only resistances to be overcome by a motor truck are road friction and the force of gravity.
Both road and grade resistance are in direct proportion to weight carried and are usually expressed in terms of pounds per pound. If the tractive force of the driving-wheels be expressed in the same terms, it becomes a simple matter to compare the resistance to be overcome with the force available for doing it. It makes no difference in truck ability what the location of the driving-wheels and the disposition of the load may be. The author uses eight formulas in developing his thesis and compares his equations with those of H. K. Thomas, C. T. Myers and Mr. Roebuck.
The problem of speed versus economy of operation is fully discussed. High speed costs money. Excessive high-gear ability costs money. As the fuel problem becomes more serious something must be done to improve truck economy and to enable truck engines to operate on the poorer grades of fuel. Marine engines use kerosene satisfactorily, something that has never been done successfully by either trucks or passenger cars.
The author believes that the use of pneumatic tires for motor trucks will greatly widen the field, but emphasizes the fact that high-speed pneumatic-tire trucks and slow-speed solid-tire trucks are two fundamentally different propositions and should be treated as such.
He states that to operate successfully on pneumatic tires a truck should be specially designed for this service and have the characteristics of a large passenger chassis.


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