2003 E85 suspension upgrade

[MinneapolisJeff]

Fresh out of storage and aiming to replace the OEM strut/shock setup on my E85. I think I'm settled with Bilstein. So, which product to go with? B4 vs. B6 vs. B8

https://workshop.bilstein.com/en-us/...ison-b4-b6-b8/

I do have the 3.0i engine w/ sport suspension, so that probably narrows it down to B6 vs. B8. The link above points out that B8s accommodate lowered springs, but I'm just interested in keeping the stock spring height. Which to choose?

[86Zed]

In general the B4= Touring (Black), B6= Heavy Duty (Yellow HD), B8= Sport (Yellow)

The B6 is designed around the OEM BMW spring and usually provides a significantly stiffer feel thank stock. In your situation I would go with B4 and be done with it.

Take a deeper look at this thread on the other Z4 forum https://z4-forum.com/forum/viewtopic.php?t=106967

[MinneapolisJeff]

Originally Posted by 86Zed

In general the B4= Touring (Black), B6= Heavy Duty (Yellow HD), B8= Sport (Yellow)

The B6 is designed around the OEM BMW spring and usually provides a significantly stiffer feel thank stock. In your situation I would go with B4 and be done with it.

Take a deeper look at this thread on the other Z4 forum https://z4-forum.com/forum/viewtopic.php?t=106967

great link, helpful information in there, thx

you think the B4 over the B6? I do like a firmer ride, and the roads up here in the Minnesota upper midwest are not the smoothest, so I guess the question is how much do I want to feel those bumps?

[86Zed]

It’s a tough call I would direct that to E85/E86 non-M owners with real world experience on these exact dampers.

I also live in the twin cities area and removed the KW Clubsport setup on my Z4M in favor of bilstein B16 PSS10 - a big improvement but someday I may try to soften it up even further (the chassis is so rigid to begin with)

[MinneapolisJeff]

Much of the vendors listing the B4s for sale have notes that specify for standard suspension, that's where my question is coming from. Feels like the B6 might be closer to the sport suspension setup.

[86Zed]

Originally Posted by MinneapolisJeff

Much of the vendors listing the B4s for sale have notes that specify for standard suspension, that's where my question is coming from. Feels like the B6 might be closer to the sport suspension setup.

There is lot of conflicting information out there surrounding B4/B6 usage in stock 'M-Sport' applications. Email or call Bimmerworld - they can likely provide a quick no nonsense answer. Locally I would try calling Orr Autosport in Eden Prairie

Suspensions are highly subjective and so many factors can affect the resultant ride comfort and performance (lowering, springs, bushings, wheel/tire size and compound, alignment, etc.)

[MinneapolisJeff]

Originally Posted by 86Zed

There is lot of conflicting information out there surrounding B4/B6 usage in stock 'M-Sport' applications. Email or call Bimmerworld - they can likely provide a quick no nonsense answer. Locally I would try calling Orr Autosport in Eden Prairie

Suspensions are highly subjective and so many factors can affect the resultant ride comfort and performance (lowering, springs, bushings, wheel/tire size and compound, alignment, etc.)

another good tip, I had Orr do some work for me last year, I'll give them a call

[MarinerZ4C]

I just replaced the struts/shocks on my 2006 3.0si Coupe (Sport suspension). I went with B4's after talking to a BMW master tech (son of a friend). He knows I daily-drive the car, and he recommended either Sachs or B4's because he felt the coupe was so stiff already that I would find the B6's too harsh. Suspension is personal and subjective, but I'm very happy. The suspension feels plenty controlled, but supple. I'm in Minnesota, and only a few of the roads around me are really smooth

I was also initially put off by Bilstein's recommendation that B4's be fitted to both Sport and non-Sport suspension. I think that they figure the non-Sport owners are probably looking for a firmer-than-stock ride and thus the B4 can do double duty. The longer stroke of the B4's compared with OE units did not seem to increase my car's static ride height.

[MinneapolisJeff]

Originally Posted by MarinerZ4C

I just replaced the struts/shocks on my 2006 3.0si Coupe (Sport suspension). I went with B4's after talking to a BMW master tech (son of a friend). He knows I daily-drive the car, and he recommended either Sachs or B4's because he felt the coupe was so stiff already that I would find the B6's too harsh. Suspension is personal and subjective, but I'm very happy. The suspension feels plenty controlled, but supple. I'm in Minnesota, and only a few of the roads around me are really smooth

I was also initially put off by Bilstein's recommendation that B4's be fitted to both Sport and non-Sport suspension. I think that they figure the non-Sport owners are probably looking for a firmer-than-stock ride and thus the B4 can do double duty. The longer stroke of the B4's compared with OE units did not seem to increase my car's static ride height.

thanks, another vote for B4s, appreciate additional Minnesota feedback

[B328iC]

I have a 2003 with the M-sport suspension as well. After talking with a few engineers at Bilstein I followed their recommendation to get the B8's. The B4 are straight replacements for a stock, NOT M-sport, suspension. The B6's are and upgrade for the stock, NOT M-sport, suspension. The M-sport is a factory lowered suspension and is best mated to the B8's. Hope this helps. BTW I started with engineers in Ohio and ended up talking with the Motorsports group in CA.

[T-Bears]

I have a 04 2.5i with Sport suspension. I recently bought the original BMW sports suspension with the slightly shorter shaft to retain suspension travel. I also wanted to restore original ride with shock valving that matches the spring rate of the OEM Sport springs. I'm very happy with how my Z4 handles now. Shocks and struts were blown.

B4 has the closest valving setup to OEM. I've tried the other Bilstein variants but they were all on the firmer side for my taste. I live in Los Angeles and the roads are super HORRIBLE.

My SLK Mercedes is on B4's and the ride is awesome, it's so close to OEM smooth. No regrets.

[MinneapolisJeff]

Originally Posted by MinneapolisJeff

another good tip, I had Orr do some work for me last year, I'll give them a call

So I spoke w/ Chris Orr and he threw another suggestion into the mix- SACHS. He said this would be the best bet to achieve the stock sport suspension feel that I said I'm after. Also mentioned the Bilsteins are pretty stiff, and in some cases, affect the ride height (negatively).

Sachs is the OEM product, correct? Only trouble i'm seeing with this brand is that I still see tons of mentions about applicable for standard suspension.

So now I don't know what to do LOL. But I'm starting to understand the recommendation for the B4s over the other Bilstein products.

[86Zed]

Chris knows his stuff and SACHS were mentioned elsewhere in a few threads. Sometimes OK to not overthink it and go with OE/OEM solution, it will certainly feel much better than a tired old suspension. Have you addressed any of the bushings?

Most people going to Bilstein are seeking a slight drop (myself included), and for street driving it is stiffer than I would prefer.

I see a items on FCP Euro delineating between stock and sport suspension, on the rear with Sachs/Koni/Bilstein/OEM, less so on the front unless you go BMW. Deeper investigation necessary

[MinneapolisJeff]

Now that I've just gotten my Zed out of storage here in 2025, circling back around to this thread...

My suspension project is still pending, I had some life events come up, and then some other issues on the car to fix first, so my hope is to resume this search this year. At least until I just saw the pricing of some of the OEM suspension part. Holy tariffs. The front Sachs struts are about $466/ea at ECS Tuning currently, that's not gonna fly for me right now lol. I may need to fall back to my 2nd best choice in order to procure some sort of deal on a suspension package of some kind.

[T-Bears]

Yeah, OEM Sport Suspension is pretty expensive. I paid about the same price. I measured the B4 shafts and it was a little longer than my factory sport setup . Whenever my suspension gets shot, I’m just going to buy coil overs and be done with it.

I can’t complain, fresh factory suspension rides pretty darn good.

[86Zed]

Originally Posted by MinneapolisJeff

The front Sachs struts are about $466/ea at ECS Tuning currently, that's not gonna fly for me right now lol.

Rear Struts: 33526764001 (x2) OEM BMW $209ea [Schmiedmann]
Front Struts: 31316761895 & 31316761896 $322ea [Schmiedmann]

Bilstein struts are obviously cheaper and you can source through RockAuto vs the more expensive ECS, Turner, and FCPEuro spots.

Rear Struts: Bilstein Touring $75ea (BIL-19158983), HD $106ea (BIL-24104906)
Front Struts: Bilstein HD $235 (BIL-35124092), (BIL-35124108) $235

To be honest you will want to replace the bump stops, shock mounts, and other rubber while you are in there. Not worth taking all of it apart twice.

[thrak410]

I updated mine with Koni Yellows last year, made a huge difference in ride and handling.

Just throwing it out there that you don't have to stick with Bilstein or Sachs.

[MinneapolisJeff]

Originally Posted by thrak410

I updated mine with Koni Yellows last year, made a huge difference in ride and handling.

Just throwing it out there that you don't have to stick with Bilstein or Sachs.

yeah, I'm aware of Koni as well, been focusing on the other brands for the moment

how much was the stock ride height affected?

[Piper1]

Originally Posted by MinneapolisJeff

yeah, I'm aware of Koni as well, been focusing on the other brands for the moment

how much was the stock ride height affected?

What springs are you deciding on? My roadster on eibach koni yellow adjustable combo is roughly 1” lower than my stock coupe both had/have sport suspension. Here’s how it looks on the roadster vs stock coupe.

[thrak410]

Originally Posted by MinneapolisJeff

yeah, I'm aware of Koni as well, been focusing on the other brands for the moment

how much was the stock ride height affected?

My ride height didn't change, on stock springs.

[jwolf]

There always seems to be issues on B4 or B6 with M-Sport fitting. Koni Yellow adjustable and you can dial in B4-B6 range. Also, look into the Rogue engineer rear shock mounts that allow you never have to pull the trunk apart again to dismount or adjust the shocks.

[MinneapolisJeff]

Originally Posted by jwolf

Also, look into the Rogue engineer rear shock mounts that allow you never have to pull the trunk apart again to dismount or adjust the shocks.

I assume this is the E46 pkg on their site? (didn't see products listed for E85)