The Denison review. [volume] (Denison, Iowa) 1867-current, 1919-02-26
ual rates, and for that reason will not
be considered further.

| udl dlSS, lOl lAdL 1OuooA Will Aol
be considered further.
The wild III of tire is important On
soft road surfaces a wide tire is dis.
tinct advantage over narrow one.
Twenty-four tests by the Missouri ag-
ricultural experiment station with IL
inch tires on soft surfaces gave an av-
erage tractive resistance of 1856 pounds
per ton while under the same condi-
tions except with six inch tires the av-
erage tractive resistance was 290
pounds per ton. The 1 u inch tires re-
quired the expenditure of about one
third more energy. The same is not
true on firm surfaces, especially on
hard surface roads. In fact there is
but little to be gained by using wide
tires on hard roads except to distrib-
ute the weight of the load safely over
a greater area.
Tractive resistance increases as the
diameter of wheels decreases. The
average of nine tests by the Missouri
Iexperiment station on various types
of roads gave tractive resistances per
ton as follows: For so inch wheels,
130 pounds; for SO inch wheels, 14S
pounds, and for rs inch wheels, 1856
pounds. The 26 inch wheels caused
an increase in effort Of forty-three
per cent more than was required for
SO inch wheels.
The mere contact between the
wheel tire and the surface is the most
important and the most variable part
Of all the resistance. In registering
the total tractive resistance, an in
strument of the recording and inte-
grating type known as the Iowa dyna-
mometer was used. This was design
ed by Professor Davidson while on the
staff of Iowa State college. 1t auto
matically measures the draft, sup
plies direct reading, and at the same
time retains graphic record made
on strip of paper drawn under re-
cording pencil. The record so pro-
vided supplies an accurate check up
ION the reading made direct.
Numerous tests have been made
with the above instrument on al
sorts of road surfaces in Iowa and
other states. The following tabula-
tion is averaged results showing the
total tractive resistance in pounds for
loads of. 1000 pounds gross, on level
grades.
The following gives the kind of
road, condition Of road and the tract
i've resistance in pounds:
Brick or concrete, snlooth'surfaced,
80 pounds.
Macadam, best, so pounds.
Macadam, good, so pounds.
Gravel, best, 80 pounds.
Gravel, good, 100 pounds.
Earth, smooth, dry, hard, 100 pounds
Earth, average, $50 pounds. (
Earth, mud, stiff but firm under
meath, 200 pounds. ....e. b.. ..s-.
Earth, mud, stiff and deep, 300
pounds. s... -,
Earth, deep, sticky, clay, 450 pounds.
When pulling loads up grade an ex-
ira effort is required to overcome
grade or gravity resistance which is
constant, increasing directly as both
load and grade. 1t can easily be fig
ured by the approximate formula :, G
equals p w in which G equals grade
or gravity resistance in pounds. P
equals per cent of grade expressed in
Fhundredths, and w equals weight of
load in pounds. Example: Given a
load Of one ton gross to pull up ten
per cent grade. Figure grade or grav-
ity resistance. Substituting in the
preceding formula G equals .10X20OO.
Equals 200 lbs. or one-tenth the weight
of load. Similarly for a one per cent
grade, G equals .01X2000 lbs. or 20
lbs, per ton. For level or zero grade,
we have G equals .O0X20O0 or O. lbs.
Grade or gravity resistance is 20
pounds per ton for each one per cent
increase in grade.
Numerous tests have proven that
team of horses in average condition
can exert a pull equal to one-tenth of its
weight and travel along steadily at
about three miles per hour without un-
due fatigue, and that when hauling
up steep grade it can exert a pull
equal to one.fourth of its weight for
distances not to exceed about twelve
hundred feet, and that in starting
loads, and for pulls of SO to 100 feet
the team can exert pull equal to one
half of it's weight.
From the above tables of resistance
for various surfaces, it appears that a
team of twelve hundred pound horses,
|exerting pull equal to one-tenth of
it's weight, or 24O pounds, on level
road, could, without undue strain,
walk along steadily with loads as fol-
lows: tons gross on brick or con-
crete surface, tons gross on the best
of macadam, 8 tons gross on the best
of gravel, "a tons on dirt road in the
best of condition, ton gross in mud
with firm foundation beneath the sal
low mud, and that the same team
would have a good load to pull stead
lily at three miles per hour if it hauled
the averoge empty wagon in deep
sticky clay.
The more improved the road sur
faces become, the more noticeable will
the grades become, and the more will
heavy grades limit the weight Of loads.
We have not the time and space to
discuss this at present but may do so
in the near future. Suffice it here to
say that the surfacing of heavy grades
does not deliver the usually expected
results. and does not permit you to in
crease greatly the maximum load for
your team to haul.
Reduce the grades first, then i'm
prove the surfaces and watch the loads
increase and the hauling costs de-
crease.