|  |
|
|
What is the offset of a
wheel?
The offset is the distance from the
mounting face of the wheel,
where it mounts against the wheel hub, and the
centreline of the wheel's width.
It will be expressed as a distance, usually
in mm and called ET.
Why is offset important?
When a car is designed, the suspension is
configured in a certain way,
which uses wheels with a certain offset. If
this offset changes, then the
distance between the mounting face and the
centre of the wheel changes
and this can affect the handling of the car. One
situation is tram-lining,
where the car wanders, following imperfections in
the road surface, rather
than running straight. Another possible situation
is torque steer, where the
steering pulls from one side to the other under
acceleration.
What is the PCD?
PCD stands for Pitch
Circle Diameter and is a measure of the wheel stud/bolt
hole locations. The
PCD is a circle with its centre at the centre of the face of
the wheel. The
centres of the mounting holes are equally spaced around this
circle. So for
example, a 4x100mm PCD means four mounting holes, equally
spaced around a
100mm diameter circle form the centre of the wheel.
What
does a Spigot Ring do?
This is a plastic ring that sits inside
the alloy wheel, locating it centrally on
the car's wheel hub. The spigot
doesn't form part of the mechanical join between
the car and the wheel,
that's done by the wheel nuts/studs. The Spigot simply
makes sure that the
wheel is located centrally on the hub. If it wasn't, the wheel
nuts/studs
would have to centre the wheel and if the wheel wasn't perfectly central
on the hub, there could be
possible vibration and balance problems.
|
|
Basket
