Jaguar XJ (2008 year). Service manual — part 65

261

Wheels and Tires

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Wear

All tires 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 tire.

It is illegal, in certain countries, to
continue to use tires after the tread has
worn to less than 1.6 mm over three
quarters of the width and the entire
circumference of the tire.

It should be noted that the properties of
many tires alter progressively with wear.
In particular, the wet grip and aquaplaning
resistance are gradually but substantially
reduced. Extra care and speed restriction
should therefore be exercised on wet
roads as the effective tread depth
diminishes.

Incorrect wheel alignment will accelerate
tire wear. If there is wear on the inner or
outer edges of the tread pattern it will be
advantageous to have the cause detected
by having the wheel alignment checked.

Do not interchange tires from side to side,
front to rear or vice versa.

Damage

Excessive local distortion can cause the
casing of a tire to fracture and may lead to
premature failure. Tires should be
examined especially for cracked walls,
exposed cords, etc. Flints and other
sharp objects must be removed from the
tire 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.

Tire repair

Damaged tires should be replaced with
new tires fitted. They must not be repaired
in view of the high performance capability
of the vehicle.

Tire replacement

When replacing tires, it is preferable to fit
a complete vehicle set. If either front or
rear tires only need to be renewed, new
tires must be fitted as axle sets.

After new tires have been fitted the
wheels need to be dynamically balanced.

Do not fit tires with a different tread
pattern, size or speed rating.

The installation of replacement tires with
steel cord body plies in the tire sidewall
may cause malfunction of the TPMS and
is not recommended (cord material
information is moulded on the tire
sidewall).

Additionally, if your vehicle was equipped
with run-flat tires, replacing them with
tires that are not identical to those
originally fitted may cause malfunction of
the TPMS, and is not recommended.

JAG0393G

Wheels and Tires

262

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Always check your TPMS indicator after
replacing one or more tires on your
vehicle.

Tire ageing

Tires degrade over time, even when they
are not being used. It is recommended
that tires generally be replaced after six
years of normal service. Heat caused by
hot climates or frequent high loading
conditions can accelerate the ageing
process.

You should replace the spare tire when
you replace the other road tires due to the
ageing of the spare tire.

263

Wheels and Tires

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TIRE QUALITY GRADES

United States Department of
Transportation/Uniform Tire Quality
Grades

The following information relates to the
tire grading system developed by the
National Highway Traffic Safety
Administration which will grade tires by
tread wear, traction and temperature
performance.

Tread wear

The tread wear grade is a comparative
rating based on the wear rate of the tire
when tested under controlled conditions
on a specified government test course.
For example, a tire graded 150 would
wear one and a half (1.5) times as well on
the government course as a tire
graded 100.

The relative performance of tires depends
upon the actual conditions of their use,
however, and may depart significantly
from the norm due to variations in driving
habits, service practices and differences
in road characteristics and climate.

Traction - A, B, C

The traction grades, from the highest to
the lowest are AA, A, B and C. The
grades represent the tire’s ability to stop
on wet pavements as measured under
controlled conditions on specified
government test surfaces of asphalt and
concrete. A tire marked C may have poor
traction performance.

!

WARNING:

The traction grade assigned to this tire
is based on braking (straight ahead)
traction tests and does not include
acceleration, cornering hydroplaning
or peak traction characteristics.

Temperature - A, B, C

The temperature grades A (the highest), B
and C represents the tire’s resistance to
the generation of heat and its ability to
dissipate heat when tested under
controlled conditions on a specified
indoor laboratory test wheel.

Sustained high temperature can cause
the material of the tire to degenerate and
reduce tire life, and excessive
temperature can lead to sudden tire
failure.

The grade C corresponds to a level of
performance which all passenger car tires
must meet under the Federal Motor
Vehicle Safety Standard No. 109.

Grades B and A represent higher levels of
performance on the laboratory test wheel
than the minimum required by law.

!

WARNING:

The temperature grade for these tires
is established for a tire that is properly
inflated and not overloaded. Excessive
speed, under-inflation or excessive
loading, either separately or in
combination, can cause heat build-up
and possible tire failure.

Wheels and Tires

264

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WINTER (SNOW) TIRES

The tires fitted as original equipment are
designed with a rubber compound, tread
pattern and width specially suited for high
speeds in normal road conditions, but
they are less suitable during extremes of
low temperatures, snow and ice. The use
of winter tires will considerably improve
the vehicle’s handling during these
conditions.

It is recommended that only Jaguar
approved winter tires are used
(see page 274).

Tire directional indicators must be
rotating in a clockwise direction when
viewed from the right-hand side of the
vehicle, and counter-clockwise when
viewed from the left-hand side of the
vehicle.

Do not exceed the tire speed rating when
using winter tires.

Winter tires must be used in vehicle sets,
that is, fitted on all four wheels.

SNOW CHAINS

Snow chains, of the recommended type,
may only be fitted to rear wheels.

Contact your Jaguar Dealer for details
and availability of approved snow chains.

The maximum speed when using snow
chains is 48 km/h (30 mph).

Remove the snow chains immediately the
roads are clear of snow.

Ensure the fitting instructions supplied
with the snow chains are kept in a safe
place, for example, with this literature
pack.

Note: Dynamic Stability Control MUST be
switched OFF when using snow chains.