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TYRE WEAR.
Recent changes in the fundamental prin
ciples of wheel and axle geometry and
steering assembly of practically all auto
mobiles, have left manv autnmnhiln
dealers and service shops groping in the
dark to find the cause of steering trouble'
and tyre wear.. These changes did not
come gradually; they came with a rush,
as-a necessary development due to the
sudden widespread . preference for balloon
tyres and the urgent, need for additional
braking power, given by four-wheel brakes.
The sudden demand for balloon tyres a
few years ago exposed weaknesses of
the. ten current steering construction in
a glaring light, because balloon tyres
brought four times the tread surface in
contact with the road at every turn of
the wheel. And how costly this would
prove in case of misalignment is amply
illustrated by the fact that scientific
demonstrations show that when' pitch and
toe-in are one inch out of true, a tyre
is dragged sideways a mile for every 16
miles of travel. The first step to cor
rect this situation .was to 'dish' the front
wheels or give them the angle of pitch;
so . that ' the wheels were closer to
gether at the bottom than at the top.
Second, it was' necessary to 'pigeon-toe'
them, or give them the angle of toe-in;
so, ;that the front part of the wheels
were closer together than the rear. And
then in order to get away from the hard
steering, and keep the weight of the car
on the centre rib of the tread as the
wheels were turned from side to side,
it became necessary to tilt the front axle
backward, giving the angle known as
castor. The correct angles of the pitch,
toe-in and caster had to be determined
by experiment; and it was found to vary
according to the length of the wheel
base, the weight and balance of the
car, the positions of the springs, and
many other factors. With the result that
specifications vary for every .make of car
and truck, and virtually every model. And
whenever the delicate balance of the
steering geometry became upset by such
a shock as striking a bump or hole, or
by sagging of the springs, unequal ten
sion ot the brakes, or by any one of many
other incidents of ordinary driving, the
car developed a tendency .to weave back
and forth on the road, to wander, to be
hard to turn, to scuff tyres, or to shiminy.
Any one of these might prove too
costly in its damage, to tyres, or so dan
gerous for driving that correct wheel
and axle alignment becomes imperative.
Motorists are advised by the Dunlop :Rub:
ber Co. that whenever undue tyre ' wear
is apparent, it is always' advisable to
have the alignment of the wheels and
axles checked iip by an expert.
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