Join Date: Apr 2000
Location: Danville, CA USA
There is some equivocation going on in this thread that makes it difficult for people to make sense of the bushing material comparisons being made.
If you are going to compare bushing material A to material B, you need to keep all of the other variables constant. This means the volume of material (geometry of bushing) must be the same. Comparing Delrin bushings in stock FCAs to polyurethane bushings in MM FCAs is invalid. The bushings have vastly different volumes of material. Think of this as a limit problem in Calculus. As the volume of material in the bushing approaches zero, all materials behave exactly the same. The less thickness of material is in a bushing, for a given material, the stiffer the bushing is going to be.
Polyurethane has more friction, it cold flows, and has less mechanical strength than Delrin. Delrin is self lubricating, has less friction, more mechanical strength, doesn't cold flow and is stiffer. The Delrin bushing will last much longer since it doesn't cold flow and has higher mechanical strength. It will transmit more noise and harshness since it is stiffer. The ride quality will be better, because it has less friction. This allows the suspension to move more freely over small bumps.
Any road noise that gets to the driver has to go through several series elements in the car. Tire to hub to spindle to ball joint to FCA to bushing to k-member to chassis to seat to driver as an example. If all of the items in that list are very stiff except one, when you replace that last item with a stiff one, the noise and harshness is going to go up a lot. However, it doesn't really make sense to say that the last item installed caused a lot of NVH.
Since virtually everything experienced by the driver goes through the tires, they have the single largest effect on NVH. Their NVH characteristics change quite a bit with air pressure and a lot from new to old tire as the rubber wears away. Without using the same tires, at the same air pressure and tread depth, you can't make good NVH comparisons.
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