wear indicators, the mark being TWI, an
arrow, or the tyre manufacturer’s symbol (see
illustration). Tread wear can also be
monitored with a simple inexpensive device
known as a tread depth indicator gauge (see
illustration).
3Ensure that tyre pressures are checked
regularly and maintained correctly (see the
Specifications at the beginning of this Chapterfor pressures). Checking should be carried out
with the tyres cold, and notimmediately after
the vehicle has been in use. If the pressures
are checked with the tyres hot, an apparently-
high reading will be obtained, owing to heat
expansion. Under no circumstancesshould an
attempt be made to reduce the pressures to
the quoted cold reading in this instance, or
effective under-inflation will result.
1•9
1
Tyre Tread Wear Patterns
Shoulder Wear
Underinflation
(wear on both sides)
Check and adjust pressures
Incorrect wheel camber
(wear on one side)
Repair or renew suspension
parts
Hard cornering
Reduce speed!
Centre Wear
Overinflation
Check and adjust pressures
If you sometimes have to inflate
your car’s tyres to the higher
pressures specified for maximum
load or sustained high speed,
don’t forget to reduce the pres-
sures to normal afterwards.
Toe Wear
Incorrect toe setting
Adjust front wheel alignment
Note: The feathered edge of
the tread which characterises
toe wear is best checked by
feel.
Uneven Wear
Incorrect camber or castor
Repair or renew suspension
parts
Malfunctioning suspension
Repair or renew suspension
parts
Unbalanced wheel
Balance tyres
Out-of-round brake disc/drum
Machine or renew
4.2A The TWI mark on the side of the tyre
shows the position of the tread wear
indicator bands
4.2B A tyre tread depth indicator should
be used to monitor tyre wear - they are
available at accessory shops and service
stations, and cost very little
Weekly checks
Most garage forecourts have a
pressure line which combines a gauge
to check and adjust the tyre pressures,
but they may vary in accuracy, due to
general misuse and abuse. It therefore
pays to carry a good-quality tyre
pressure gauge in the vehicle, to make
the regular checks required and ensure
pressure accuracy.
4Note any abnormal tread wear (see
illustration). Tread pattern irregularities such
as feathering, flat spots, and more wear on
one side than the other, are indications of
front wheel alignment and/or balance
problems. If any of these conditions are
noted, they should be rectified as soon as
possible.5Under-inflation will cause overheating of the
tyre, owing to excessive flexing of the casing,
and the tread will not sit correctly on the road
surface. This will cause a consequent loss of
adhesion and excessive wear, not to mention
the danger of sudden tyre failure due to heat
build-up.
6Over-inflation will cause rapid wear of thecentre part of the tyre tread, coupled with
reduced adhesion, harder ride, and the
danger of damage occurring in the tyre
casing.
7Regularly check the tyres for damage in the
form of cuts or bulges, especially in the
sidewalls. Remove any nails or stones
embedded in the tread, before they penetrate
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