APRIL 2019 53TECH TALK
Hands up how many of you have never
rotated your tyres. I don’t think it’s something
that many do, but it’s recommended by
manufacturers like Goodyear and Continental,
and they’re not going to be wrong about
something like this. It’s basically the practice
of moving your tyres between front and back
so they wear evenly.
Obviously, you can only do this if you’re
running a square set-up all-round but, it
does make sense as naturally the tyres on
the driven wheels will always wear faster
because they’re having to put the power on
to the road. As a general rule, it’s best to have
the tyres with most tread at the back of your
car. Why? Well, if you’ve got more grip at the
back then the worst that will happen is a bit
of understeer when you’re really pushing on,
so you can back off to come out of that. But,
run with worn tyres at the back and your car
will be prone to snap oversteer in slippery
conditions, as the rear end will be loose.All modern tyres are radial in design, and they’re all made using virtually the same
construction process. The main variations relate to the actual compound being
used and the tread pattern that the tyre wears. A tyre begins its life with the steel
beads, which are covered in rubber to form the tyre bead and the basis upon
which the rest of the tyre can be built. The tyre liner is next, and this is a non-
porous, nylon-reinforced rubber layer that joins the beads and forms the inner
layer of the tyre, keeping the air where it belongs, between the wheel and the
tyre itself.
Next come the body plies, made from nylon-reinforced rubber again, and these
give the tyre its shape. The number of plies varies but, on a typical road tyre, you’ll
fi nd two or three. Steel belts are next, and these steel-reinforced sheets of rubber
give the tyre strength and durability, and the number and type of these used will
help to determine the fi nished tyre’s speed and load ratings. Typically, there will
be two or three of these layers in most road tyres. The layers are then covered
with a fi nal coating of nylon-reinforced rubber, before the tread cap is applied.
As its name suggests, this is the fi nal layer of thicker rubber into which the
tread pattern is cut. The tyre’s not fi nished yet, though; at this stage it’s ‘green’
and all those layers of rubber will need to be cured before the tyre can be put to
work on the road. The curing process involves applying heat and pressure, which
causes the layers to bind together, creating a rubber laminate, and gives the tyre
its desired characteristics. The tread pattern is also indented at this stage and the
sidewall information is added, too.TYRE ROTATION? TYRE CONSTRUCTION
RUBBER COMPOUNDS
A tyre’s surface isn’t just made of rubber, there’s a combination of diff erent materials used
and it’s this mix that determines how the fi nished tyre will perform in diff erent conditions
and at diff erent temperatures, the amount of grip and traction it’ll provide and how long
it will last. Obviously, a tyre engineer’s dream would be to create a tyre that performs
perfectly in all conditions, lasts a long time, is quiet and comfortable yet still delivers
impressive performance. Ultimately, though, that’s all but impossible.
Each tyre will obviously be designed with a specifi c goal in mind and some
compromises will be inevitable so, for example, a very high performance tyre will use
a softer compound that performs best in dry conditions, but its wet grip might be
compromised. Alternatively, a tyre designed for optimal fuel economy and low wear will
use a harder compound that won’t off er the highest levels of grip or traction.
There are numerous ingredients that make up any one tyre’s rubber compound, and
altering these and their ratio results in diff erent performance characteristics. Some of the
ingredients include: carbon black, which provides reinforcement and abrasion resistance;
silica, which helps to prevent the build-up of heat; sulphur, antioxidants and antiozonants.
If it sounds complicated, that’s because it is. But, by working with these ingredients, tyre
companies are able to change how a tyre behaves in any given situation.