15. GLOSSARY
Tyre
A tyre consists of: I-the actual tyre, II- the rim (wheel),
III-the air chamber (in tube type tyres), IV-pressurised air.
The tyre must:
- withstand a load,
- ensure driving power,
- steer the vehicle,
- aid handling and braking,
- aid vehicle suspension.
I - Tyre The tyre is the main part of the complex that is
in contact with the road and is therefore designed to
support the internal air pressure and all other stress
arising from use.
A tyre section shows the various parts it consists of:
1 - The tread. It is the part in contact with the road while
the tyre is rolling. It comprises a rubber compound
and a "pattern" suitable for ensuring good resistance
to abrasion and good grip in dry and wet conditions, as
well as quiet operating conditions.
2 - Edge or bracing. This is a metal fabric or textile insert,
in the area of the outer bead part. It protects the casing
plies from rubbing against the rim.
3 - Casing. This is the resistant structure and comprises
one or more layers of rubber plies. The way the plies
comprising the casing are arranged give the structure
its name. The following structures are possible:
Conventional: the plies are inclined and arranged so that
the strands comprising a ply overlap with those of the
adjacent ply. The tread, which is the part of the tyre in
contact with the ground, is part of the sidewalls and so
during rolling, sidewall flexure is transmitted to the tread.
Radial: the casing consists of one or more plies with
the cords in a radial direction.
A radial casing in itself is quite unstable. To make it
stable and prevent incorrect tread movement in the
area of contact with the ground, the casing and the
tread are reinforced with an annular structure, usually
called a belt. The tread and sidewall work with differ-
ent, independent rigidities, so during rolling, sidewall
flexure is not transmitted to the tread.
4 - Side ring. This is a metal ring comprising several steel
strands. The casing plies are secured to the side ring.
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