(c) No vehicle of four wheels or less whose gross weight with load is over 24,000 pounds is permitted to operate over or along a public highway. Any vehicle having a greater weight than 22,400 pounds on one axle, or any vehicle having a combined weight of 800 pounds per inch-width of tire concentrated upon the surface of the highway (said width of tire in the case of solid rubber tires to be measured between the flanges of the rim) is also barred by the provisions of this law, with the following exception:
PROVIDED, that in special cases vehicles whose weight including loads whose weight exceeds those herein prescribed, may operate under special written permits, which must be first obtained and under such terms and conditions as to time, route, equipment, speed and otherwise as shall be determined by the director of licenses if it is desired to use a state highway; the county commissioners, if it is desired to use a county road; the city or town council, if it is desired to use a city or town street; from each of which officer or officers such permit shall be obtained in the respective cases. Provided, that no motor truck or trailer shall be driven over or on a public highway with a load exceeding the licensed capacity.
Chain Drive. Trucks equipped with a chain drive should be supplied with an extra set of chains so that they may be changed and cleaned every week. To clean the chains, they should be soaked in kerosene which removes the dirt, grease and gum that has accumulated. By doing this the life of the chains will be quadrupled. The small amount of time that it takes will pay.
Top. The truck should come equipped with a top over the driver’s seat that is easily detachable. In bad weather the driver should be protected from the elements, but the top should be removed in good weather as it is in constant danger of being broken during loading. Many operators leave the top off entirely and the driver must dress for the weather. A good demountable top will add to the comfort of the men and often helps to keep a good man at his job.
TRAILERS
The development of the trailer has made motor truck logging practical. Every truck has greater tractive power than it can utilize in the propulsion of the ordinary load. Its limitations are due to a short-bulk carrying capacity and not to any lack of pulling power. The ordinary truck has a draw-bar pull of 2600 pounds. The draw-bar pull per ton of load varies from the minimum of 50 pounds on a level pavement to 250 pounds on a level dirt road, depending upon the character of surface.[5] Twenty pounds of additional pull are required for each degree of gradient. For example, a fore and aft plank road offers a resistance of about 60 pounds pull to a ton of load. If this were located on a seven per cent grade, it would require a 60 pound pull to overcome the load resistance plus seven times twenty or 140 pounds additional pull for the grade, a total of 200 pounds to pull one ton. Dividing 2600, the draw-bar pull of the truck, by 200, the resistance offered by road and grade, gives 13 tons as the load that can be pulled by the truck over this surface and grade. As this must include the weight of the trailer, which when equipped for logging is about three tons, it leaves a total of 10 tons that the truck can pull. This is equivalent to about 3000 feet B. M. of Douglas fir logs, the average load that is hauled. While such an adverse grade as cited in this illustration is avoided if possible with a loaded truck, the illustration will serve to show the pulling capacity of the truck. The hauling of loads of this size would be impossible without the use of the trailer. The normal load, then, may be increased two, three, or even four times, by the use of the trailer, over the maximum load that can be carried by the truck alone.
[5] Operating Cost of Motor Truck Computed. Timberman. Feb., 1918. Page 60.
Objection to the trailer that it tends to shorten the life of the truck is hardly worth consideration. According to a careful analysis it has been estimated that the use of the trailer does not shorten the life of the truck by more than one year, which is of little consequence when the saving due to the size of the load that can be carried is taken into consideration.