Volvo S80 Owner's Manual page 119

All tyres have a dimension designation, such as 215/55R16 93W.
These tyre size designations, which are used by all tyre manufacturers,
can be interpreted as follows:
215 section width (mm)
55 relationship between the section height and breadth (%)
R means radial tyre
16 wheel rim diameter in inches (")
93 code digits for maximum permissible tyre load, in this
case 650 kg
W specifies that the tyre is manufactured for speeds up to
270 km/h (167 mph)
Your car is fully approved, which means that you may not deviate from
those dimensions and performance ratings indicated in the vehicle
registration. The only exception from these regulations concerns winter
tyres and studded tyres, which may have different dimensions and a
different speed rating than indicated in the registration. If you select tyres
with different dimensions, do not drive at speeds faster than those
permitted. The most common speed ratings are indicated in the following
table:
Note: maximum permissible speeds indicated.
Q 160 km/h, used most often with studded tyres
T 190 km/h
H 210 km/h
V 240 km/h
W 270 km/h
When you change tyres: be sure to use the same type (radial), dimension,
designation, and brand on all four wheels. Otherwise, there is a risk that
the handling characteristics of the car could change. Check with your
dealer regarding dimensions which are available for your car. Keep in
mind that the road surface can determine how fast you may drive, not the
tyre speed rating.
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Bear in mind that tyres are perishable goods - after a
few years they begin to harden while their friction
properties deteriorate little by little. Try to use fresh
tyres when changing.
This is especially important for winter tyres. The week
7700444d
and year of manufacture is indicated with 4 digits (e.g.
1502 indicates tyres manufactured week 15, 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 discoloura-
tion.
The age of the tyre can be determined by the
marking, see illustration.