The Moment of Inertia of a nonpoint object is calculated by the
formula: I = k x R2 x M (measured
in kg m²)
Where: M is the mass R is the
radius of the object from the center
of mass k is a dimensionless constant
called the inertia constant that varies
with the geometry of the object in
For example k = 1 for a thin-walled
cylinder around its center or k = ½ for
a solid disc around its center.
The advantage of decreased
weight is that you will achieve an
incremental improvement in your
vehicles power to weight ratio. The
smaller diameter clutch is lighter
even though an intermediate plate
and extra clutch disc is added.
This is because the effect of the
weight decreases dramatically as the
diameter gets smaller. i.e. the weight
is proportional to the radius squared.
If the radius is halved the weight is decreased 4 times.
The advantages of lowering
the Moment of Inertia of a clutch
assembly are two fold. Firstly there is
less inertia required to spin the clutch
assembly therefore requiring less of
the engine power to spin up to speed.
The net effect is the vehicle is able to
The second is that the clutch discs
will not continue to spin on for
as long and therefore enable gear
changes to happen quicker. The net
result again is faster acceleration and
less time when there is no power
being transmitted to the wheels.
The Moment of Inertia is a measure
of an object’s resistance to changes in
its rotation rate. The symbol ‘I’ is used
to refer to the Moment of Inertia.
The Moment of Inertia is of
particular interest with clutches and
Flywheels because to accelerate a
vehicle we need to overcome the
vehicles resistance to acceleration or
its Moment of Inertia. Reducing the
Moment of Inertia of the Clutch Kit has
the same effect as adding power to the
engine, enabling it to accelerate more
quickly. It is important to note that the
Moment of Inertia is proportional to
the Radius squared. So a small change
in the Radius or Diameter of a clutch
has a dramatic effect on the Moment
of Inertia. For example an increase in
Diameter of 40% i.e. from 200mm
to 280mm approximately equates
to a doubling of in the Moment of
Inertia or a doubling of the resistance
to changing the rotation rate or a
doubling of the power required to
accelerate this clutch.