ROLLING STOCK EQUIPMENT

In general two plans are followed in building a motor truck. The first is to build a rigid truck so that it will resist all shocks and distortions that come from rough and uneven roads. The second plan is to build a flexible body so that the chassis will “give” rather than resist when subjected to hard strains. Although the rigidly-built truck may be entirely satisfactory for most forms of trucking, it is practically impossible to build one on the rigid principle that will stand up under the heavy strains to which a logging truck is subjected unless it is to be operated over good paved roads. When only ordinary unpaved public roads are available, flexibility is one of the most important characteristics to look for when selecting a truck. Where the operator is hauling over his own pole or plank road this consideration does not play so important a part, as the road bed then is more likely to be free from holes and irregularities.

All makes of trucks are more or less alike in general construction, differing only in minor details, so that the personal whims of the buyer will largely determine the kind he will select. It is advantageous to have as long a distance as possible between the driver’s seat and the bunk over the rear axle, in order to allow more of the load to be carried by the truck, and less by the trailer, giving better traction to the drive wheels, but necessitating extra strong rear springs and axles.

The type of power transmission best suited to the use of the logging truck is a question that has received a great deal of attention. There are three general methods of transmitting the power: (1) by chain; (2) by worm drive, and (3) by internal gear drive. Each has its advantages. It is claimed by many that the chain drive saves many hours of “shut-down time” due to the fact that if anything breaks in the transmission, it will be a link in the chain as this is the weakest point. It is then only a matter of a few minutes to insert another link. With the worm driven vehicle, a break in the transmission requires an expensive shut-down before the matter can be repaired. The worm drive, on the other hand, very seldom breaks if proper care is used.

The chain drive also allows the replacement of the sprocket with one of a larger or smaller diameter thereby giving a higher or lower gear ratio, which cannot be done with the worm gear. This seems to be of some advantage to an operator when changing his setting from one with a short haul and steep grades where a low gear ratio is required, to one where the haul is long and fairly level, and where speed in transit is an advantage.

On the other hand, in starting on slippery grades or wherever the traction is poor, the worm drive will give better traction than a chain drive because there is difficulty in taking up the slack that is always present in the chain before letting in the clutch fully. The slightest jerk given to the wheels when the slack is taken up is likely to cause them to spin, thereby losing all the tractive power of the drive wheels. In the worm gear there is no slack to take up and the power can be applied more gradually, thus reducing the chances of spinning the wheels and losing the traction.

The question of the weight of the truck used for logging purposes is not as important now as it will be in the future. Laws are being passed in nearly every state limiting the maximum weight to be carried on each wheel by trucks using state or county roads so that the total weight of the truck without load will be important. When operating over state or county roads the load is limited to from 2400 to 3000 feet, B. M., of Douglas fir, depending upon the locality. In such cases, it is an advantage to have a lighter truck, say one of 31⁄2 tons capacity. By adding additional leaves to the rear springs of a truck of this capacity it may be made to carry a larger load than it would be possible to put on a 5-ton truck and still comply with the law. The pulling power of the 31⁄2-ton truck and the 5-ton truck is practically the same so that the difference in dead weight between the two may be carried in a profitable manner by adding four or five hundred feet B. M. of logs. Another advantage of the lighter weight truck is speed. The 31⁄2-ton truck is geared to make from 14 to 16 miles an hour, while the 5-ton truck is usually limited to from 10 to 12 miles an hour.

Whenever the legal weight limit does not enter into the problem, as in operating over a pole or plank road for the entire distance, it is, of course, advantageous to carry the largest loads possible. In such cases a 5-ton truck with an 81⁄2-ton trailer is the most profitable investment. This allows a much larger load to be carried in proportion to the overhead charges. The disadvantage of the 5-ton truck is that it is very heavy and unless the roads are good, it will easily sink into the ground and cause trouble. A common fault of the 5-ton truck today is the overweight of the front end, which is too heavy for the width of tire on the front wheels. This can be very easily overcome by the use of wider tires.