The Washington herald., 1921-11-20
EARNING CAPACITY
FOR AUTO VEHICLE.
HAS TWO FACTORS
Directly Depends Upon
Total Mileage and Ton
mage Handled.

poses Is directly dependent upon
the total mileage covered daily and
the total tonnage handled. That H.
Its ability is rated in tom miles
Ability 10 also dependent upon the
hexibility Of q transportation unit
In its application - work Of Fary-
ing demands. SO that 1t VIII keep
engine power and man power en-
ployed during all the working
hours. The ma ximum ton-mIleage
can not be obtained unless the
vehicle 10 performing useful work
continually. While running, the
vehicle Is saving money. While
standing still IL IL of no greater
service than q warehouse. Thus, the
most important factor of highway
transportation Is to keep the
vehicle moving.-A. A. d.
There are two ways OF accom-
plishing this. by the use Of de-
mountabie bodies or trailers. Either
of these permits loading or unload
ing one unit while the other unit
is being moved by the vehicle. The
first method presents a number OF
Disadvantages. the first cost is high
and they can not be as readily
adapted to all classes of work.
Special equipment is necessary for
handling the bodies and unless the
vehicle has a large capacity. little
time can be saved. The trailer has
an advantage in that IL can be
adapted to any vehicle, large or
small, and is of particular value In
handling large. bulky loads which
can not be carried readily on the
conventional chassis because OF the
unusual overhang. They. of course.
III
efficient on city streets or level
vantage on billy or bad roads, II
they decrease the operating speed
OF the power unit.
The trailer has the same relation
to the truck that a freight car ha.
to locomotive. Trucks have
ample power to pull an additional
load. and like the locomotive or any
draft animal, can pull more than
they can carry. This is due to the
vehicles latent draw-bar pull
which Is only brought into action
when the vehicle Is required to pull
rather than carry load. In start
ing a loaded four wheeled vehicle.
the force required to put il in mo-
tion is directly proportional to that
portion OF the load concentrated
over the rear wheels. other condi-
lions of weight distribution over
front and rear wheels and road con-
ditions as t. type Of pavement and
degree OF grade being equal. Under
these conditions the power trans
mitted from the engine TO the rear
axle is sufficient to start the load
by means of the proper gear reduc-
tion between the engine and the
rear wheels. This gear reduction
is always made low enough to start
the vehicle under full load in low
gear under the most severe condi-
lions possible under average work
ing requirements.
When a semi-trailer is employed.
the major portion OF the load is
generally concentrated over the
trailing wheels so that that portion
concentrated over the vehicle
wheels is less than in the case Of a
four-wheeled vehicle and as
truck alone. This reduction in the
weight concentrated over the rear
wheels does not require the full en-
CINE power to start the load and
the difference between the power
used under this condition and that
required to start the load when
carried on the truck itself is con-
verted into draw-bar pull to tow the
major portion of the load carried
on the trailing wheels
As the power required TO pull a
load is less than that required to
carry 1t. the power required to move
the load over the trailer wheels can
be obtained from the engine with
out overlooking IL. Tests have
proven that the average fully load
ed truck will develop a draw-bar
pull equal to one-half OF its rated
capacity. Thus a one-ton truck will
develop a draw-bar pull of one-haIf
ton or 1000 pounds. and a fve-tcn
truck. two and one-half tons or
5000 pounds
The draw-bar pull required to
move a truck and trailer varies