Maintenance 7 - 19
Wear
All tyres fitted as original equipment
include tread wear indicators (TWI) in
their tread pattern. When the tread has
worn to a remaining depth of 1.6 mm the
indicators appear at the surface as bars
which connect the tread pattern across
the full width of the tyre.
It is illegal, in certain countries,
to continue to use tyres after the tread
has worn to less than 1.6 mm over three
quarters of the width and the entire
circumference of the tyre.It should be noted that the properties of
many tyres alter progressively with wear.
In particular the ‘wet grip’ and
aquaplaning resistance are gradually but
substantially reduce
d. Extra care and
speed restriction should therefore be
exercised on wet roads as the effective
tread depth diminishes.
Incorrect wheel alignm ent will accelerate
tyre wear. Fins on the inner or outer
edges of the tread pattern are caused by
excessive toe-in or toe-out respectively.
As fins may also be caused by high
cornering speeds or road camber, it is
advantageous to have the cause detected
by having the wheel alignment checked.
Tyre repair
It is recommended that damaged tyres
are discarded and new tyres fitted.
They must not be repaired in view of the
high performance capability of the
vehicle. Damage
Excessive local distortion can cause the
casing of a tyre to
fracture and may lead
to premature failure. Tyres should be
examined especially for cracked walls,
exposed cords, etc. Flints and other sharp
objects must be removed from the tyre
tread; if left in they may work through the
cover. Clean off any oil or grease
contamination by using a suitable
cleaner.
Caution: Do not use paraffin
(kerosene), because this has a
detrimental effect on rubber.
Tyre use after vehicle storage
After a long period of a vehicle standing,
tyres may become locally distorted with a
flat area. This will cause an uneven ride
for a few miles until the tyres have
warmed up and the ‘flat’ rounds off.
However, to reduce the effects of
flat-spots, the tyres of a stored vehicle
may be inflated to pressures not
exceeding 60 lbf/in² (4.2 bar, 420 kPa,
4.3 kg/cm²).
