Hello folks

I just installed some Hardrace rubber rear trailing arm bushings, and they are a lot harsher over bumps than my worn OEM bushings. One thing I noticed was that while the OEM bushings have cut-outs to allow the entire trailing arm to move forwards and back, the Hardrace ones are basically a solid chunk of rubber. I think a lot of the harshness come from the wheel no longer having any forwards-backwards compliance to absorb shock, but instead being forced to move up and down.

Because the Hardrace is solid rubber, it also has a lot higher stiffness in the directions of:

A: rotation with respect to the axis of the bushing shell
B: sideways (trying to pull the bushing out of the trailing arm)
C: bending the piece that runs thru the center of the bushing with respect to the axis of the bushing shell
D: trying to pull the center of the bushing off center, e.g. pulling backwards on the trailing arm

So in comparison, the OEM bushing is:
A: medium, B: medium, C: soft, D: soft

A poly bushing is:
A: free to move?
B: ???
C: stiff
D: stiff

And a spherical is
A: free to move
B: depends on unit?
C:free to move
D: no movement

Now the Hardrace is moderately stiff in all four categories

So the question is which of these deflection are helpful/hurtful to good handling and which for ride comfort? This is my guess so far, but please correct me if I am wrong:

A: bushing should be free to rotate since the strut is supposed to take care of this.
B: I don't know. I would think it's better that it's soft in this direction so that the compensator arm can set the toe properly. If it is stiff in this direction, it puts extra stress on the compensator arm and LCA.
C: I don't know. It seems like the geometry is supposed to be set by the compensator arm and LCA
D: It seems like looser is better for ride comfort, but worse for handling.

Anyway, it looks like the OEM bushings are designed to allow the TA to flop forwards and backwards a bit. I'm considering switching back to new OEM ones if it will give back the ride comfort without hurting the handling too much.

 

If you are really looking for performance ?... Use the PCi Spherical trailing arm bearings. A little harsher riding, but perform soooo much better than bushings (of any kind)
If you are looking for a combination of comfort and performance... then use the stock or Mugen Bushings. You will never achieve the same performance advantage with bushings that you will get with PCi Sphericals
It sounds like you are not <U>really</U> serious about performance, and I assume this is a street car?

Kiwi

 

Yes, this car is also my daily driver.
The reason I asked was that I haven't heard of any other solid rubber bushings, and was wondering about the forwards-backwards compliance.

 

Kiwi is the man