The enterprise. [volume] (Wellington, Ohio) 188?-1899, 1897-12-22
FARM AND GARDEN.
TRAcTlvE FORCE TESTS.
Resistance of Road Surfaces Meas
rrnh hr The nrnnAnnrrnnIn -.

Resistance of Road Surfaces MeRss
ured by the TractOgrnph. ,s9@
Traction may be defined as the re-
Blstance which a stationary body Of
fers to motion, or the force required to
move given weight on agiven surface.
1t is found that the resistance offered
by different surfaces varies consider
ably, and consequently the force re-
quired to impart motion to bodies on
them varies likewise. Experiments to
determine the force of traction on diff
ferent surfaces have been made from
time to time, during the last 60 years,
the latest being those conducted by the
road inquiry office of the department Of
agriculture.
In order to secure continuous rec
ord as well as measure of the tractive
force, an apparatus called tSacto-
graph, arranged to make q g<aphic
record, was attached to ioaded
wagon which was driven over different
surfaces and gradients. These tests
gave the following results:
The force of traction is not constant,
but varies with the character of tine
road at any given instant, being most
uniform on the smoothest surfaces,
and constantly increasing the varia-
tions as the roughness of the road in
creaseS until 1t becomes merely a
quick succession of violent pulls. A
team is thus subjected to a continuous
| jerking motion, which greatly in
creases the fatigue caused by the sim
pie pull necessary to move load. On
asphalt the variation of traction is very
small; on smooth macadam it is some.
what more, and on an ordinary dirt
road it is seven or eight times as great
as on macadam. If the dirt road be
actually bad the result is practically
u series of heavy blows transmitted tc
the team through the collars, and these
blows are estimated to be doubly al
fatiguing as a steady pull, even at the
maximum traction of the road. On 6
smooth road the traction itself is less
and is comparatively constant, so tha
the pounding effect on the team dis
appears, thus enabling them to ust
their whole strength in hauling mucl
heavier loads with less power.
The effect of the variation of trac
tion, due to regularity of road surfac,
is analogous to the effect of vibration OF
a bicycle rider. Every wheelmal
knows how vibration increases as road
become rough; but, owing to pneumat
ic tires, the comparison is not entirel,
fair Ride a pneumatic-tired whee
over a piece of poor macadam; thel
ride one with cushion tires and finall,
one with solid tires, and the enormou
increase in vibration and greater diff
Guilty of propulsion will illustrate tn
changes in tractive force on teams go
ing from good to poor roads.
During the tests small mules eas
lily drew over 5000 pounds up
ten per cent. grade of smootl
macadam, but were unable to pul
the same load down a six pc
cent. grade of sand, though the indi
Gator showed that nearly double powe
: was applied, and three-quarters of tn
| load was removed before it could b
started. A loaded wagon, with tive
inch tires, drawn over dirt road Gu
1t into deep ruts, while the same loa
, with four-inch tires only smoothed tn
. surface, and it was found that tn
traction on the road where the narro,
/ tires had been used was double what
: was on the section where the wide tire
were used.
J The tractive force for different roa
-, surfaces, expressed in terms of tn
number of pounds required to move on
ton, as found in these tests, is as fo
: lows:
= Tractiy