WHEELS
AND
TYRES
the recommendations, the owner
will
obtain the
best results both from the tyres and the
car.
Tyre Pressures:
Correct tyre pressures for 5.50"-15" are
:
Front
22
lbs. Rear
24
lbs.
Note.-Pressures should be checked when the
tyres are cold, such as after standing overnight,
and not when they have attained normal running
temperatures.
Pressures shown are for normal motoring
when sustained high speeds are not possible.
Special Pressures
for
High
Speed
Motoring
(a) For touring at sustained speeds in
excess of 85/90 m.p.h., pressure in
front and rear tyres should be in-
creased by
6
lb. per sq. in.
(b) For predominantly and regularly high
speed touring of continental
type,
pressures in front and rear tyres
should be increased by 8 lbs. per
sq.
in.
Tyres lose pressure, even when in sound
condition, due to a chemical diffusion of the
compressed
air
through the tube walls. The
rate of loss in a sound
car
tyre is usually between
1 lb. and
3
lbs. per week, which may average
10% of the total initial pressure.
For this reason, and with the additional
purpose of detecting slow punctures, pressures
should be checked with a tyre gauge applied
to
the
valzr!
not less often
than
once per week.
Any unusual pressure loss should be in-
vestigated. After making sure that the valve is
not leaking the tube should be removed for a
water test.
Do not over-inflate, and do not reduce
pressures which have increased owing to in-
creased temperature. (See
"
Factors Affecting
Tyre Life and Performance," page
3).
Valve Cores and Caps
Valve cores are inexpensive and it is a
wise precaution
to renew them
periodically
Valve caps should always be fitted, and
renewed when the rubber seatings
have become damaged after constant
use.
Tyre Examination
Tyres o~z cars submitted for servicing
should be examined for
:-
Idation pressures.
Degree and regularity of tread wear.
Misalignment.
Cuts and penetrations.
Small objects embedded in the treads,
such as flints and nails.
Impact bruises.
Kerb damage on walls and shoulders.
Oil and grease.
Contact
with
the
car.
Oil
and grease should be removed by
using petrol sparingly. Paraffin is not
sufficiently volatile and is not recom-
mended.
If oil or grease on the tyres results
from over-lubrication or defective oil
seals suitable correction should be
made.
(c)
Repair
of
Injuries
Minor injuries confined to the tread
rubber, such as from small pieces of
glass or road dressing material, require
no attention other
than
the removal of
the objects. Cold filling compound or
"
stopping
"
is unnecessary in such
cases.
More severe tread cuts and wall rubber
damage, particularly
if
they penetrate
to the outer ply of the fabric casing,
require vulcanised repairs. The Dun-
lop Spot Vulcanising Unit is designed
for this purpose and it is also suitable
for
all
types of tube repairs.
Injuries which extend into or through
the casing, except clean nail holes,
seriously weaken the tyre. Satisfactory
repair necessitates new fabric being
built in and vulcanised. This requires
expensive plant and should be under-
taken by a tyre repair specialist or by
the tyre maker.
Loose gaiters and
"
stick-in
"
fabric
repair patches are not satisfactory sub-
stitutes for vulcanised repairs and
should be used only as a temporary
<L
get-you-home
"
measure if the
tyre
has any ap reciable tread remaining.
They
can
o
t!
en be used successfilly
in
tyres which are nearly worn out and
which are not worth the cost of
vulcanised repairs.
Clean nail holes do not necessitate
cover repairs. If a nail has penetrated
the cover the hole should be sealed by
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