Volvo XC90 Owner's Manual page 149

Wheels and tyres
General
Driving characteristics and tyres
The tyres greatly affect the car's driving
characteristics. The type of tyre, dimensions,
tyre pressure and speed rating are important
for how the car performs.
When changing tyres, ensure that tyres of the
same type and dimensions, and preferably
also the same make, are fitted to all four
wheels. Follow the recommended tyre
pressures specified on the tyre pressure
label, see page 151.
Designation of dimensions
The dimensions are stated on all car tyres.
Example:
225/70R16 102H.
225 Section width (mm)
70 Ratio between section height and
width (%)
R Radial ply
16 Rim diameter in inches (")
102 Tyre load index (in this case 615 kg)
H Speed rating (in this case
210 km/h).
Speed ratings
The car is approved as a whole, which means
that dimensions and speed ratings must not
differ from those specified on the vehicle's
registration document. The only exception to
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these conditions is winter tyres (both those
with studs and those without). If such a tyre is
chosen, the car must not be driven faster than
the speed rating of the tyre (for example,
class Q can be driven at a maximum of
160 km/h).
Remember that traffic regulations determine
how fast a car can be driven, not the speed
class of the tyres.
Note! Maximum permitted speeds indicated.
Q 160 km/h (used only on winter
tyres)
T 190 km/h
H 210 km/h
V 240 km/h
W 270 km/h
New tyres
Tyres are perishable. After a
few years they begin to
harden at the same time as
the friction capacity/charac-
teristics gradually deteri-
orate. Therefore aim to get
as fresh tyres as possible when you replace
them. This is especially important with regard
to winter tyres. The week and year of
manufacture, the tyre's DOT marking
(Department of Transportation), are stated
with four digits, for example 1502. The tyre in
the illustration was manufactured in week 15
of 2002.
Tyre age
All tyres older than six years should be
checked by an expert even if they seem
undamaged. The reason for this is that tyres
age and decompose, even if they are hardly
ever or never used. The function can
therefore be affected due to the tyre's
constituent materials being broken down,
and it should then not be used.
This also applies to spare tyres, winter tyres
and tyres saved for future use.
Examples of external signs which indicate
that the tyre is unsuitable for use are cracks
or discolouration.
The age of the tyre can be determined by the
DOT marking, see illustration above.