WHEELS
AND
TYRES
driving and braking are greater than
when the tyre is part worn. Higher
tread mileages will usually be obtained
if new tyres are fitted in the autumn
or winter rather than in the spring or
summer. This practice also tends to
reduce the risk of road delays because
tyres are more easily cut and penetrated
when they are wet than when they are
dry. It is therefore advantageous to
have maximum tread thickness during
wet seasons of the year.
(f
)
Road Surface
The extent to which road surfaces
affect tyre mileage is not always
realised.
Present day roads generally have better
non-skid surfaces than formerly. This
factor, combined with improved car
performance, has tended to cause
faster tyre wear, although
dcvelop-
ments in tread compounds and patterns
have done much to offset the full
effects.
Road surfaces vary widely between one
part of the country and another, often
due to surfacing with local material. In
ACTUAL
PATH
!!
NO
SLIP
ANGLE
/
/
some areas the surface dressing is
coarser or of larger
"
mesh" than in
others. The material may be com-
paratively harmless rounded gravel or
more abrasive crushed granite or knife
edged flint. Examples of surfaces pro-
ducing very slow tyre wear are smooth
stone setts and wood blocks but their
non-skid properties are poor.
Bends and corners are severe on tyres
because a car can be steered only by
misaligning its wheels relative to the
direction of the car. This condition
applies to the rear tyres as well as to the
front tyres. The resulting tyre slip and
distortion increase the rate of wear
according to speed, load, road camber
and other
f'dctors. (Fig.
0.)
'l'he effect of hills, causing increased
driving and braking torques with which
the tyres must cope, needs no elabora-
tion.
Road camber is a serious factor in tyre
wear and the subject is discussed on
page
8.
An
analysis of tyre performance
must
include road conditions.
U
CENTRE
OF
TURN
WITH
NO
SLIP
ANGLE
Fig.
6
Diagrammatic Illustration of Slip Angles.
5
To Next Page
Loading...
