Imperial Valley press., 1928-02-04
MILLER COMPANY
EXPLAINS CAUSE
OF TIRE SHIMMY
Engineers Study Odd
Shaking Felt Often BY
Motorists.

is offered by the Vaughn Auto 90.
valley distributors of Miller "Gear-
ed-to .theRoad" tires, from mater
ial sent out from headquarters at
Akron, Ohio.
No doubt large percentage OF
motorists have had little or no ex-
perience with shimmy Shaking OF
the front end.) Those who|have
had any experience with violent
high speed shimmy realize that it
presents a very serious problem to
both automotive and tire engineers.
Although both industries have
studied this condition very thorough
ly the cause of the trouble still re-
mains somewhat mystery. Some
progress has been made in eliminat-
ing it but as yet no one has advanc-
ed sure cure.
There are two types of shimmy,
low speed shimmy and high speed
shimmy.
The first is usually due to slack,
loosoress, or wear in the steering
mechanism. This tyre of shimmy
has been observed in many makes
Of ears which have been run on
ongv high pressure tires. Some
times the application of balloon
tires seem to accertuate this trou-
BILE but cases have been observed
where it is minimiZed. No case
has thus far come to our attention
which we could not overcome by
tightening or rebushing steering
mechanism or changing axle tilt
Should Reduce Speed
The second type-high speed SHIN
mv-is closely related to the first
type in that the front wheels seem
TO oscillatc from one side to the
other instead of rolling forward
along a given path in the same
plane; but the oscillations are much
more rapid and the range from side
to side is less. But in addition 70
the oscillations there is also an up
and down movement. II high speed
shimmy becomes violent the speed
Of the car should be reduced at once
Automobiles vary greatly in their
susceptibility to this high speed
shimmy. The following is n brief
summary of observations on this
type of shimmy.
l. An increase in the air pressure
in the front tires will greatly re-
duce or eliminate high speed SHIN
my.
9. 1t has been possible to reduce
or eliminate shimmv to some ex-
tent by making stiffer tires. How
ever. when the air pressure is al
lowed to run down shimmy is Jus,
about as bad on these stiff tires o.
on the regular balloon tires. Wha'
has really been accomplished IL
only that the air pressure polnr
where shimmy starts has been re-
duced to lower pressure. Further
more. the stiffer construction is OBJ
iectionable because it is working IN
the opposite direction from the de-
sired effect which we have endea-
vored to gain. with the adoption OF
the balloon tire.
8. High speed shimmy is not
caused by loose or worn steering
Dul pO
by such a condition.
4. It is not purely balloon tire
trouble-the tendency can be found
in cars on high pressure tires.
5. Some cars develop shimmr
period as low as 40 miles per hour
which is passed when sreed is in
creased so the car NAV be driven
at the rate Of so to 20 miles Der
hour without any shimmy. Other
ears show no signs of shimmy un'
til a speed of so miles per hour or
more is reached.
Happens Suddenly
g. Shimmy is synchronism or
vibrations of the autom obile ana
road shocks timed with the rare o.
revolution Of the wheels. These
synchronize to produce sh'mr'o
within certain speed ranges. a car
usually requires certain kind Of
road vibration to cause it to shim-
my. Asphalt pavements with low
rolling or wavy Irregularities ar
very conducive to shimmy. A car
may run a great many miles with
out the slightest sign Of shimmy
and then shimmy badly upon strik-
ing the type Of pavement which is
conducive to shimmy. However, no
matter what tvnn of pavement Is
encountered the car will not shin
my unless it is in the proper speed
range.
7. Tread design has an effect on
the susceptibility and intensity to
shimmy. The combination ribbed
design or plain ribbed tread are the
best of any designs we have tried
in reducing shimmy.
8. Balanced wheels. tires. inner
tubes, ETC., are beneficial but do
not eliminate shimmy. Putting a
very badly balanced combination OF
tire, tube and wheel on n car that
did not shimmy, would not cause
this condition TO develop. On the
other hand putting the best combi-
nation of balanced tire, tube and
wheel on car that would shimmy
did not entirely eliminate the trou-
BILE.
9. Shimmy bears relation to
the position and angle Of king pins
and the layout and linkage Of the
complete steering mechanism.
There are many different makes
of steering gears used. A number
are quite different in design, theory
and functionino. Naturally they
do not react the same to shimr'
We are glad, however, to say tho
cor nonufocturnra fodav have done