The Washington times., 1922-12-24
means TO PREVENT
|sK|DD|NG EXPLAINED.
Rear Wheels Slip Easily On
Quick Application Of
Brake Pressure.
BY b. J. LEMON,
United States Tire Company.

United etstes Tire Company.
Why an automobile skids In of in
terest to q motorist. but what TO do
to prevent skidding and what to do
when the car. 10 skidding are equally
important topics.
The main cause Of skidding of rear
wheels Of motor cars IL due to the
action Of the brakes operating
through the rear wheels. Slddding,
of course, normally occurs only
when the roads arc slippery.
An automobile wheel rotates and
progresses over the highway In but
one direction or plane. This direc-
tion for the rear wheels is deter
mined by the front wheels under con-
troll of the driver. While the rear
wheels grip the ground and rotate
they control the direction Of the car.
However. a. soon a. the rear
wheels are locked by the brakes
they begin to slide, and a. they slide
sidswiss practically a. easily ~ for
ward they lose the power to direct
the car.
WHEELS SLIDE EASILY.
Il takes comparatively little brake
friction to lock and slide rear wheels
on slippery roads because there ID
little friction between the tire and
the road surface. When once the
driving wheels begin to slip the car
10 kept In motion by the force Of
inertia acting at the cars center Of
ton is opposed by the resistance Of
all four wheels on the ground, q re-
sistancs that 10 greater in the ro-
tating front wheels than In the sid.
Ing rear wheels. Unless the com
binsd ground resistance Of all
wheels. tending TO stop the car, acts
on the same point as the force of
inertia tending to carry the car for
ward. there results what In called a
'foroe couple" which causes the car
to skid or spin around.
After the wheels once start 70
slip q very small force couple"
will produce siidding. and the skid
distance u dependent upon the
magnitude Of the force couple
which in turn depends on car speed
and weight. Turning the front
wheels In the direction of the rear
wheel skid helps to reduce skid
ding because II reduces the magni-
tude of the force couple" Also
periodically releasing and rsapply-
Ing the brake 20 the rear wheels
can set q grip offsets forward slip
and consequent side skid.
Two means are employed to pre-
vent skidding In motor vehicles.
These are the use Of non-skid or
rough tread tires and Of anti-skid
chains. Non-skid tires are designed
to give forward traction and to
prevent side slip. A. long as there
10 traction the rear wheels will
turn. and as long a. the rear
wheels turn there will be no Sc
rious side slip. unless the front
wheels are blocked.
Non-skid tires furnish reliability
and safety In driving-reliabiiity. In
permitting the vehicle to operate
successfully oyer almost any kind
Of road and during all seasons Of
the year, and safety by permitting
the vehicle to hold the road at all
speeds. and allowing the brakes to
be most effective,
Non-sl<id treads on tires were
used first on rear wheels and now
are considered absolutely essential
for such uses. Later non-skid tires
were placed on front wheels be-
cause the treads prevented front
wheel skidding. ~ well a. permitted
the rotation or exchange Of the
front and rear tires.
QUALITIES ANALYZED.
A we'll designed non-skid tread
should give on rear wheels suffi-
cient forward traction to permit
the car to operate without chains
under most road conditions and At
the same time insure against side
slip. It must permit quick and
smooth response TO clutch. accelera-
tor and brakes. It must not I'm
pair greatly ease Of steering when
used on front wheels. II must not
set up vibration In the car nor
produce disagreeable hummins
noises. II should present an At,
traotive appearance. The Royal
Cord Tread 10 regarded as the best