First of all I'm aware of mixed reviews on Bilstein HD, especially on E39 forum where some absolutely hate them.
I believe it comes to personal preference and some people probably do incorrect install or even combine them with wrong springs.
I have Bilstein HD combined with stock springs on both E39's and even my wife and 6 year old daughter don't complain abut harsh ride.
Yes, they're stiffer than OEM Sachs but I'd call it firm and controlled ride instead of harsh, but again, I'm aware of different personal preferences.

So, about to get rid of rear air suspension (already purchased ECS tuning OEM springs kit and 2 rear Bilstein HD shock)
Also since my front left CV joint boot got recently torn, instead of replacing the boot I decided to put complete GKN shaft with OEM seal since I got really good price and the PO had dealer install one on other side.

Considering I have to disassemble number of components and the fact that I have 106k on original struts I decided to all install both front Bilsteins, do alignment and be done.

They're the most expensive part at $229 each but I'll probably never have to replace them ever again.

So, anyone running Bilsteins and their impressions. Thanks!

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2010 BMW M6 * Black Saphire Metallic * Full Black Merino Leather
2019 BMW X3 M40i * Alpine White * Mocha Leather