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Bilstein b4 or b6

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Sajk
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Bilstein b4 or b6

Post by Sajk » Thu May 11, 2023 5:41 pm

Looking to replace my struts and shocks. Don't really want any firmer as it's pretty firm with stock shocks. Also dont want lower. What is the experience of the forum?

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Bilstein b4 or b6

Post by Rockhopper » Thu May 11, 2023 6:42 pm

As a general rules shocks don't control the height of the car, that's down to the spring length. But - do you actually have an M?

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Bilstein b4 or b6

Post by plenty » Thu May 11, 2023 7:35 pm

Unless I'm mistaken you can't get B4 for the Z4M, only B6. And, as above, ride height is determined by springs.

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Bilstein b4 or b6

Post by Sajk » Fri May 12, 2023 7:33 am

Yes have M. My bad on the shock ride hight.

What do people generally replace Oem shocks with on these? My understanding is that b6 is about 20% firmer than OE which will surely hurt low speed ride quqlity.

Mine is great at speed and well controlled but pretty bad round town over bumps etc. Looking to improve that without compromising control at speed.

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Bilstein b4 or b6

Post by Argenta » Mon May 15, 2023 9:00 am

Eibach Pro springs made mine a lot more comfy in general (and lower obviously) but I'd imagine with Billies you also get more control, they're the best.

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Bilstein b4 or b6

Post by Special Kay » Mon May 15, 2023 9:35 am

Argenta wrote: Mon May 15, 2023 9:00 am Eibach Pro springs made mine a lot more comfy in general (and lower obviously) but I'd imagine with Billies you also get more control, they're the best.
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Bilstein b4 or b6

Post by Dubbedown » Wed May 17, 2023 3:39 am

Don’t go B6, everyone and their mother loves to quote monotube lifetime warranty shocks but they ride like crap on any road surface that’s less than perfect. I’ve run multiple setups and for a non-track car, nothing beats fresh OEM hardware imho.
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Bilstein b4 or b6

Post by mmm-five » Wed May 17, 2023 9:02 am

Dubbedown wrote: Wed May 17, 2023 3:39 am Don’t go B6, everyone and their mother loves to quote monotube lifetime warranty shocks but they ride like crap on any road surface that’s less than perfect. I’ve run multiple setups and for a non-track car, nothing beats fresh OEM hardware imho.
Have you driven actually driven a standard Z4M with it's very strange/poor suspension set-up?
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Bilstein b4 or b6

Post by Argenta » Wed May 17, 2023 9:27 am

B6's are top quality stuff, should make a huge difference especially on a Z4M

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Bilstein b4 or b6

Post by Dubbedown » Wed May 17, 2023 12:17 pm

mmm-five wrote: Wed May 17, 2023 9:02 am
Dubbedown wrote: Wed May 17, 2023 3:39 am Don’t go B6, everyone and their mother loves to quote monotube lifetime warranty shocks but they ride like crap on any road surface that’s less than perfect. I’ve run multiple setups and for a non-track car, nothing beats fresh OEM hardware imho.
Have you driven actually driven a standard Z4M with it's very strange/poor suspension set-up?
Yes, I currently own 2 M’s (roadster and coupe).

A lot of people write off the factory suspension because they never had the pleasure of owning the car new. So of course when picking up the car secondhand, a tired worn suspension will leave a lot to be desired. The factory struts typically need to be replaced every 50-60k miles. But do an apples-to-apples comparison, and you’d be surprised how good the factory setup is with fresh struts, bushings (fcab rtab, etc), and mounts.

The only time I noticed my coupe understeers is on track during high g corners. But you could never replicate this scenario on any public road, and no off-the-shelf strut like the B6 will remedy this. For the 99% of usage, my coupe with fresh stock hardware handles feels amazing and I will gladly make that trade-off.

To put things in perspective, I am currently in putting my M roadster back to stock so I can list it for sale. It has full aftermarket suspension upgrade but the component I am keeping is the CSL front sway bar to help address the 1% scenario above.

I equate the B6 to a “high-performing” all season tire, i.e. an upgrade in some ways but also a compromise in many. For a sport shock, it does okay but not great on track. For street, it performs nicely on the most perfect road conditions but it’s overly harsh for anything else. Whereas fresh factory hardware is like a Michelin PS4S - it’s fantastic under most conditions and can even handle the occasional track day. However, if you wanted anything better, you might look to a 200tw or R-comp though they won’t last as long (i.e. bringing back to struts, it will need more frequent rebuilds).

The only time I would recommend Bilstein is if you went with their PSS 10 coilovers AND swapped for custom linear springs. But at that point you’ve shelled out enough money you’re not far from getting a higher tier single adjustable setup.
Last edited by Dubbedown on Mon May 22, 2023 12:13 am, edited 2 times in total.
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Bilstein b4 or b6

Post by Dubbedown » Wed May 17, 2023 12:38 pm

See this thread here

viewtopic.php?t=138219

Owner upgraded his badly worn stock suspension (with broken springs) for thr B12 kit, which is essentially the B6 struts with Eibach springs (specifically designed to be paired with B6 struts). Yet it didn’t take long for him to realize they’re too harsh and quickly swapped them out for an entry level coilovers. No knock against the BC system but just goes to show how the defacto Bilstein B6 upgrade comes with a lot of caveats.

But if it wasn’t obvious, my recommendation is if you’re sticking with factory springs, go with B4’s which are OE equivalent.
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Bilstein b4 or b6

Post by Sajk » Thu May 18, 2023 5:32 pm

Thanks for the feedback. I was afraid b6 at 20 % firmer would be like that. Bilstein don't seem to make a oem equivalent so who to choose? Buying from bmw will be expensive.

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Bilstein b4 or b6

Post by Dubbedown » Fri May 19, 2023 2:52 am

Sajk wrote: Thu May 18, 2023 5:32 pm Thanks for the feedback. I was afraid b6 at 20 % firmer would be like that. Bilstein don't seem to make a oem equivalent so who to choose? Buying from bmw will be expensive.
In general the B4 is a direct OEM replacement. B6 are valved firmer but meant to be paired with factory springs. B8’s are same thing as B6 but meant for lower aftermarket springs.

I know the B4 is offered for the non-M but I don’t recall seeking one for the M. But since your original post specified not wanting to go lower nor make the ride any firmer, seems like OE is your best bet.
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Bilstein b4 or b6

Post by 3gGT01 » Fri May 19, 2023 4:36 am

Do we know who makes the stock Z4M struts?
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Bilstein b4 or b6

Post by Rockhopper » Fri May 19, 2023 7:38 am

Sachs i would think.

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