Polyurethane or Graphite Impregnated Polyurethane are great bushing materials choices for compression applications (e.g. your anti-roll bar end-links and frame/body mounts). They are also great for lower priced replacements to stock bushings in control arm applications intended for street/strip use. However, polyurethane bushings in an application that requires rotational deflection (front and rear control arms) and axial deflection (rear control arms) will bind a lot sooner than rubber. Why worry about bind? Well, we want to avoid suspension bind because when it happens the effective suspension spring rate immediately increases to infinity. In essence, the suspension system is no longer compliant with the road surface when bind occurs (definitely NOT a good thing). The GM engineers knew that the stock rear suspension geometry would cause bind at some point in the suspension travel (as all angled arm suspensions do). This is why they chose the specific durometer rubber for the bushings that they did. At the rear you can use either higher durometer rubber bushings from the 1LE Camaro, use polyurethane, or use a Military-Specification spherical bearings. At the front, you can use higher durometer rubber, use polyurethane, or solid bushings (e.g. Herb Adams and Global West). If you want the highest performance, then the spherical bearing at the rear will allow the most consistent geometry and largest amount of suspension travel without bind. If you want the highest performance at the front, then solid bushings (which only allow rotational displacement) are what are required. For autocross, you could easily get away with polyurethane due to the smoothness and flatness of the track surface. In road racing and street circuit racing, solid and spherical bearings provide better performance at higher cost.
As for body bushings, we are all very familiar with the General's seemingly haphazard way in which it applied body bushings to the G-body cars. Well, there's nothing particularly wrong with the rubber bushings that GM put in except that one of their main design criteria was noise dampening. For the weekend warrior an upgrade to polyurethane body bushings will help stiffen the platform (remember the direction in which we are asking the bushing to do it's job) and help tie the body to the frame. There are several chassis vendors who sell these for our cars. Last time I checked, Gulstrand and PST had these available. For a much more competition oriented car, one could use the billet aluminum body bushings from Herb Adams. |
