Volvo 2008 C70 - Manual (Page 155)

07 Wheels and tyres
154
General
07
Driving characteristics and tyres
The tyres greatly affect the car’s driving char-
acteristics. 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 pres-
sures specified on the tyre pressure label,
see page 158.
Designation of dimensions
The dimensions are stated on all car tyres.
Example: 205/55R16 91 W.
Speed ratings
The car has "Whole Vehicle Type Approval",
which means that dimensions and speed rat-
ings must not differ from those specified on
the vehicle’s registration document. The only
exception to these conditions is winter tyres
(both those with metal studs and those with-
out). 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.
New tyres
Tyres are perishable. After a
few years they begin to
harden at the same time as
the friction capacity/charac-
teristics gradually deterio-
rate. 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 manu-
facture, 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 there-
fore be affected due to the tyre’s constituent
materials being broken down. In such a case
the tyre 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 unsuita-
ble for use are cracks or discoloration.
The age of the tyre can be determined by the
DOT marking, see illustration above.
205 Section width (mm)
55 Ratio between section height and
width (%)
R Radial ply
16 Rim diameter in inches (")
91 Tyre load index (in this case 615 kg)
W Speed rating (in this case 270 km/h).
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
Y 300 km/h