_Bunks._ All trucks for use in log hauling are equipped with a patent
bunk over the rear axle on which the logs rest (see illustration on page
13). This is essentially a steel I-beam (A) which grips the logs so that
they will not slip. At each end of the bunk are V-shaped iron
chock-blocks (B) held by chains which run under the I-beam and are
fastened by an iron gooseneck hook (C) so that the load is kept from
spreading. These blocks may be adjusted to any width of load. The whole
bunk is mounted on a swivel so that it will turn with the logs when
rounding a sharp turn in the road. When dumping the logs at the landing,
each block is loosened from the opposite side so that the danger of the
logs rolling off on the men is greatly lessened.
_Tires._ Solid rubber tires are generally conceded to be the best suited
for the heavy duty required in logging. The use of steel tires is
rapidly declining. The jar on the equipment is in itself enough to
condemn their use. Rubber tires double the mileage of a day's work, more
than double the life of the equipment, allow the weight of the equipment
to be cut in half, and work well on dirt, cement, or any other type of
road. The saving on the life of a pole or plank road by the use of
rubber tires is also an item of considerable importance. There are three
general types of solid rubber tires in use on the logging truck: the
so-called giant tires, the duals, and the non-skid or caterpillar tires.
It is a question as to which of the three is the best. Traction for the
drive wheels and also for the trailer wheels, if the latter are equipped
with brakes, is the problem to be solved.
The duals are satisfactory with light loads and easy grades, on cement,
brick, or other perfect surface road, but when the haul is heavy and the
braking difficult on account of heavy grades, the larger single-tread
giant tires are more efficient. During dry weather it is safe to work
with the single-tread tires on grades as high as nine or ten per cent,
but in wet weather a seven per cent grade should be the maximum unless
some extra means are taken to secure traction, and even then the wheels
will skid if particles of soil get on the surface of a plank road,
unless chains are used or the wheel is wrapped with a light cable.[4]
For very heavy-duty trucking, where resiliency and long service are
prime considerations, the giant type is rapidly superseding the old dual
type as the former contains more rubber and gives more mileage with the
least truck vibration.
[4] West Coast Lumberman. October, 1919. Page 25.
The non-skid or caterpillar tire may well be used on heavy grades or
where the traction is very poor, the general opinion being that it gives
a firmer grip on the road and makes it safer to handle the truck in wet
weather.
There is no standard width of tread for truck wheels. The widths usually
used on the drive wheels of the logging truck and the wheels of the
trailer are twelve and fourteen inches, respectively. The use of tires
of smaller width on either trailer or truck cannot be recommended. The
wider the tires on the trailer, the better it is both for the life of
the equipment and for ease in handling the load. When the surface of the
giant tires becomes worn down so that the grooves become very shallow,
it is desirable to have the tires re-grooved. They will last a great
deal longer if this is done and will also give better traction on the
road. The groove makes the tire lobes act separately on the uneven
places in the road so that only one lobe is subjected to the strain of
the irregularities instead of the whole tire. This is also true with
reference to the strains that are set up internally due to the twisting
of the rubber.