My first z3 was a 1.9, terrible tramlining, took the advice of Mr Fishwick and changed the lower wishbone bushes to poly, what a difference tramlining almost stopped, had the same issue with my 2.8, again tramlining changed to poly no more tramlining, no difference in ride, it is obvious that if other issues are involved i.e. worn suspension parts, incorrect matching tyres, non standard wheels (the bigger the wheel the more it tramlines), the problem wont go away, perhaps I was lucky that the only thing that needed doing were the lower wishbone bushes, but for £40-£50 for the part in my opinion is the best place to start (other than tyres) before starting to replace shocks, springs, rear bushes , drop links, the list goes on and on and the car can soon become a money pit. As for harder ride, just don't see how this can effect the ride to that degree, the bushes tighten up the movement to the rear wishbone, the suspension of the vehicle is not effected, the movement is a very small amount which is cured by stiffening up the bush and not the suspension. But I am not saying that what has been said is untrue, but in my experience with these poly bushes. It felt more planted to the road more responsive with the steering, perhaps mine were so badly worn in the first place that any type of new bush would have made a massive difference.
