MG MGB User Manual

0
THE WHEELS AND
TYRES
A
tyre
is
designed
so
that there
is
a
minimum
pattern
shuf■e
on
the road surface and
a
suitable distribution
of
load
over
the
tyre’s
contact
area
when de■ection
is
correct.
Moderate
underin■ation
causes an
increased
rate
of
tread
wear
although the
tyre’s
appearance
may
remain
normal.
Severe
and
persistent
underin■ation
produces
unmistakable
evidence
on
the
tread.
It
also
causes
structural
failure
due
to
excessive
friction and
temperature
within the
casing.
Pressures
which
are
higher than those
recommended
for
the
car
reduce comfort.
They
may
also
reduce tread life
due
to
a
concentration
of the
load and
wear
on
a
smaller
area
of
tread, aggravated by
increased wheel bounce
on
uneven
road surfaces. Excessive
pressures
overstrain
the
casing
cords,
in
addition
to
causing
rapid
wear,
and the
tyres
are
more
susceptible
to
impact
fractures and
cuts.
Effect of
temperature
Air
expands
with
heating
and
tyre
pressures
increase
as
the
tyres
warm up.
Pressures
increase
more
in
hot weather
than
in
cold weather
and
as
a
result
of
high
speed. These factors
are
taken
into
account
when
designing
the
tyre
and
in
preparing
Load Pressure schedules.
Pressures
in
warm
tyres
should
not
be reduced
to
standard
pressure
for
cold
tyres.
‘Bleeding’
the
tyres
increases
their
de■ections
and
causes
their
temperatures to
climb
still
higher.
Their
tyres
will also be underin■ated
when they
have cooled.
Climatic
conditions
The
rate
of
tread
wear
during
a
reasonably dry
and
warm
summer
can
be
twice
as
great
as
during
an average
winter.
Water
is
a
rubber lubricant
and tread
abrasion
is
much less
on
wet
roads than
on
dry
roads. In addition
resistance
of
the
tread
to
abrasion decreases
with
increase
in
temperature.
When
a
tyre
is
new
its
thickness and
pattern
depth
are
at
their
greatest.
It
follows
that heat
generation
and
pattern
distortion
due
to
■exing,
cornering,
driving,
and
braking
are
greater
than when
the
tyre
is
part
worn.
Higher
tread
mileages will
usually be obtained
if
new
tyres
are
■tted
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.
Road
surface
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
developments
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
some
areas
the
surface
dressing
is
coarser
than
others; the
0.6
material
may
be
comparatively harmless
rounded
grave],
or
more
abrasive
crushed
granite,
or
knife-edged
■int.
Examples
of
surfaces
producing
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
the
front
tyres.
The
resulting
tyre
slip
and
distortion
increase
the
rate
of
wear
according
to
speed,
load,
road camber,
and
other factors.
The effect
of
hills,
causing
increased driving
and
braking
torques
with which
the
tyres
must
cope,
needs
no
elaboration.
Impact
fractures
In
order
to
provide
adequate
strength,
resistance
to
wear,
stability,
road
grip,
and other
necessary
qualities,
a
tyre
has
a
certain
thickness
and
stiffness.
Excessive
and
sudden
local
distortion,
such
as
may
result
from
striking
a
kerb,
a
large
stone
or
brick,
an
upstanding
manhole
cover,
or
a
deep
pothole,
may
fracture
the
casing cords.
Impact fractures
often
puzzle
the
car
owner
because
the
tyre
and road
spring
may
have
absorbed
the
impact
without
his
being
aware
of
anything
unusual. Only
one or
two
casing cords
may
be fractured
by
the
blow
and
the
weakened
tyre
fails
some
time
later.
Generally,
there
is
no
clear
evidence
on
the
outside of the
tyre
unless
the
object
has
been
sufficiently
sharp
to
cut
it.
Wheel
alignment
and
road
camber
It
is
very
important that
correct
wheel
alignment
should
be
maintained.
Misalignment
causes
a
tyre
tread
to
be
scrubbed off
laterally
because
the
natural direction
of
the
wheel
differs
from
that
of the
car.
An upstanding
fin
on
the
edge of
each
pattern
rib
is
a
sure
sign
of
misalignment
and
it
is possible
to
determine
from
the
position
of
the ‘fins’
whether
the
wheels
are
toed
in
or
toed
out.
Fins
on
the
inside
edges
of
the
pattern
ribs—nearest
to
the
cariand
particularly
on
the
off-side
tyre,
indicate
toe-out.
With
minor misalignment
the
evidence
is
less
noticeable
and
sharp
pattern
edges
may
be
caused
by
road
camber
even
when
wheel
alignment
is
correct.
In such
cases
it is
better
to
make
sure
by
checking
with
an
alignment
gauge.
Road
camber affects
the
direction
of
the
car
by
imposing
a
side thrust
and if left
to
follow
its natural
course
the
car
will
drift
to
the
near
side. This
is
instinctively
corrected by
steering towards
the
road
centre.
As
a
result the
car runs
crab-wise.
The
near
front
tyre
sometimes
persists
in
wearing
faster
and
more
unevenly
than
the
other
tyres
even
when
the
mechanical
condition
of
the
car
and
tyre
maintenance
are
satisfactory.
The
more severe
the
average
road
camber the
more
marked
will this
tendancy
be.
This
is
an
additional
reason
for
the
regular
interchange
of
tyres.
Camber
angle
This angle
normally
requires
no
attention
unless disturbed
MGB.
Issue2.
60230

MG MGB Specifications

General

Brand	MG
Model	MGB
Category	Automobile
Language	English