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 & 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 without being crushed. 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 photo two.

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.

Problem and Solution
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, solid steel control arm bushings too, will resist compressive loading.

Figure 1. Polyurethane versus nitrile rubber under hard turning
Problem Stock rubber control arm bushings deflect excessively during harder driving causing momentary loss of alignment (excess positive camber) resulting in less contact patch and instability.	Cure Polyurethane control arm bushings resist deflection during harder turning resulting in maintenance of alignment settings, and the ability to steer through a turn with higher stability and confidence.

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 eventually swapped out all the deteriorating rubber pieces on our Fox Body Mustang with urethane. In typical detailed FordMuscle 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