What about Energy Suspension or PST - ones with polygraphite??? Since nobody has mentioned them, I'm guessing no good?
In the HD truck market, there is a company called Atro that makes some GREAT components like this for many applications. I've never looked to see if they do anything for automotive, but I'm going to look into that.
Not a fan of polys on the street , I'll admit my only experience was ocassional in a friends rustang daily driver/strip car over the years, but to harsh a ride for my taste.
