Polyurethane
vs. Nitrile Rubber
A suspension soft
part must be resilient, possess elastic memory, resist
a variety of oils, and have low material hardness (durometer).
Nitrile meets all of these requirements. But what if a
material could do all of those things and more? That material
is poylurethane. Here's the quick list of its' advantages
over nitrile rubber.
High abrasion resistance
High cut and tear resistance (shear strength)
Superior load bearing capacity (compression load resistance)
Ozone resistance
The "wonder" of polyurethane lies in its' ability
to dampen and absorb with high resistance to deformation.
However, like many of us sacrifice horsepower for torque,
polyurethane must sacrifice some material softness in
the quest for increased load bearing capacity. The photos
below show the compromise is not significant. Notice the
percentage increase in durometer is minor when compared
to the increased resistance to compression load shown
in the second photo.
Using a Durometer, polyurethane
bushings measured about 20 points higher than nitrile
rubber on the Shore
A scale.
|
A crude test showing the
superior resistance to compression load polyurethane
has when compared to nitrile rubber. |
In the demonstration above only
one example of material hardness is shown. Unlike many
aftermarket bushing manufacturers, Energy Suspension formulates
their own polyurethane. This allows a variety of durometer
ratings depending on the function and location on the
vehicle. Mounts, for example, utilize a softer material
than control arm bushings. This ensures maximum performance
without an overly stiff and harsh ride.
Problem and Cure
The figure below illustrates how poylurethane performs
against rubber when used in control arm bushings during
hard cornering. Once again, polyurethane is capable of
doing this while maintaining the low material hardness
required to dampen and absorb. See photo two above. After
all, a solid control arm bushing will also resist compressive
loading but at the expense of severe ride harshness.
| Figure 1. Polyurethane
versus nitrile rubber under hard cornering. |
Problem
Stock rubber control arm bushings deflect excessively
during hard driving, causing momentary loss of
alignment (excess positive camber) resulting in
less contact patch and instability. |
Cure
Polyurethane control arm bushings resist deflection
during hard driving, alignment settings are maintained
and the vehicle is able to steer through the turn
quicker with higher stability. |
Installing Polyurethane
We performed a
number of polyurethane installations on our 1988 Mustang
LX using components from Energy Suspension's Hyper Flex
Kit for 1985-1993 Mustangs (p/n 4-18113). Over a few
months time and during other chassis modifications we
swapped out all the deteriorating rubber pieces on our
Fox Body Mustang. In typical detailed fashion we'll
show you how we replaced:
Sway bar bushings and end links
Rack and pinion bushings
Front control arm bushings
Strut bushings
Coil spring isolators
Rear control arm bushings
Transmission mount
Motor mounts
|
