03 E85 harsh ride, Bilstein B4 w/M sport

[dfoht]

Thanks in advance for advice.
I installed Bilstein B4 shocks/struts and Suplex 06249/06231 springs on my 03 Z4 with factory sport suspension a few years ago (15K miles). It's an extremely harsh ride on the St. Louis city streets, so I'm pondering options for improvement. I'm curious of experiences with the B4 model absorbers and any conversions from M-sport to standard suspension along with any other advice to soften the ride. I'm running Continental DWS06 18" tires.

Options I'm considering
-Install standard springs and bumpers but keep the M-sport sway bars
-Install standard springs but keep the M-sport sway bars and bumpers (would this fatigue the springs???)
-Replace the springs and absorbers (model advice welcome)

This project is partly being driven as I need to replace the struts and shocks on a Z3. Many have recommended KYB, but there is a supply chain issue. The B4s are in stock, but I don't want to produce the same issue if that's the primary cause of the Z4 ride stiffness.

Doug

 

[abar121]

I guess the runflats are well gone? What wheel size are you on?

 

[Homer]

Could be bushes, I had a big improvment in ride quality after replacing the front lower control arms and bushes.

 

[dfoht]

The entire suspension system was replaced in 2017, and the lower control bushings are intact.
18" wheels and no run flats. Continental DWS06 tires.

 

[abar121]

I would fit the yellow Koni adjustable dampers with the springs you have. They don't seem to have FSD / Special Active shocks in that size unfortunately. They aren't too expensive and you can set the damping to your taste.

I have no experience of those tyres, perhaps with the treadwear rating of 560, they are on the hard side? Goodyear F1 Assy 5s ride really well and are quiet. Not an all season tyre though. Sorry, not much help.