[FaRKle!]

So a couple of people here, including myself, have noticed that the ride height increased a bit (generally about 1/4-1/2") after installing Bilstein B6/B8 dampers/struts. I decided to take my spare B6 strut and compare it alongside my OE EDC strut to take a look at the differences and try to explain why that might be. Check out the video to see why I think that happens.

Index:
0:00 Intro
0:36 Spring pad measurements
2:28 Spring orientation
3:22 Damper gas forces

[cfm56d7b]

Great video. Well done!

[thatBimmerBloke]

As per this I'll barely get 10 or 15mm drop at the front using B8 shocks paired with Eibach springs for my F32 435ix. I guess coilovers is my only option now. 10 or 15mm drop will barely make any difference when the front gap is almost 60mm.

[sspade]

FWIW... Bilstein B8 paired with AC Schnitzer spring kit worked really well for me. Definitely lowered my ride height to the perfect level (for my taste).

The actual body of the B8 damper is shorter so results may differ than that of Bilstein B6.

[Gen13 F36]

There so much inconsistencies on the information posted about shock/springs combo. I wish we could have a concise thread for all applicable combo with photo.

[FaRKle!]

Originally Posted by Gen13 F36

There so much inconsistencies on the information posted about shock/springs combo. I wish we could have a concise thread for all applicable combo with photo.

That's because most of "reviews" and user experiences posted are subjective with no technical explanation or understanding of how things actually work. There are lots of "myths" propagated on these forums due to that. This is why I crunch the numbers from damping forces/ratios to spring rates and lengths.

It amazes me how we trust so many shills on the forum (from vendors to "reviewers/influencers") who only post "this product is great!" posts without holding them to objective standards.

[FaRKle!]

Originally Posted by sspade

The actual body of the B8 damper is shorter so results may differ than that of Bilstein B6.

Do you have proof of the strut body (not damper cartridge body, which is shorter) being shorter? If the B8 strut body is actually shorter, the only place it could be would be the area between the end link mount and spring pad base.

[thatBimmerBloke]

Interesting! FaRKle! , if you check out this post, B6 with stock springs lowered the car about 10mm, while as the height increased for you:
https://f30.bimmerpost.com/forums/sh...3&postcount=11

Now I've no idea how the B8s will alter the ride height of my car, B8s are shorter than B6 In the same thread there are numbers
related to B8 vs B6 length:
https://f30.bimmerpost.com/forums/sh...6&postcount=10

EDIT: Updated links

[johnung]

Originally Posted by thatBimmerBloke

As per this I'll barely get 10 or 15mm drop at the front using B8 shocks paired with Eibach springs for my F32 435ix. I guess coilovers is my only option now. 10 or 15mm drop will barely make any difference when the front gap is almost 60mm.

60mm is almost 2.5". That sounds like too much. I'm curious. What is your method of measurement to arrive at that number?

I put a straightedge across the top of the tire sticking out directly above the center point of the wheel. Then I measure the distance from the straightedge to the lip of the fender.

[thatBimmerBloke]

Originally Posted by johnung

60mm is almost 2.5". That sounds like too much. I'm curious. What is your method of measurement to arrive at that number?

I put a straightedge across the top of the tire sticking out directly above the center point of the wheel. Then I measure the distance from the straightedge to the lip of the fender.

I guess it's more like 2.25"

[FaRKle!]

Originally Posted by thatBimmerBloke

Interesting! FaRKle! , if you check out this post, B6 with stock springs lowered the car about 10mm, while as the height increased for you. Now I've no idea how the B8s will alter the ride height of my car, B8s are shorter than B6 In the same thread a few posts below there are numbers related to B8 vs B6 length.

I think the link got missed.

[thatBimmerBloke]

Originally Posted by FaRKle!

I think the link got missed.

My bad, just updated the post with the links, please check it out now.

[johnung]

Originally Posted by thatBimmerBloke

I guess it's more like 2.25"

To shrink it I'd consider mild springs like Eibachs along with 245/45-18 summer tires like Michelin PS4S.

[thatBimmerBloke]

Originally Posted by johnung

To shrink it I'd consider mild springs like Eibachs along with 245/45-18 summer tires like Michelin PS4S.

I've a square setup of 255/40 MPSS on Apex ARC-8 18x8.5 ET38 for the summer. If Eibachs just drop it 15mm on the front with Bilstein B8 then I don't think it will make a huge difference when the gap is already this huge, they claim 20mm drop in the front but as per Farkle the drop might be lesser with Bilstein B8s Rear gap is not that bad, it's about 1.5".
245/45 along with Eibach springs would've definitely helped a little bit as the tires would've probably decreased the gap by 4-5 mm.

[johnung]

Originally Posted by thatBimmerBloke

I've a square setup of 255/40 MPSS on Apex ARC-8 18x8.5 ET38 for the summer. If Eibachs just drop it 15mm on the front with Bilstein B8 then I don't think it will make a huge difference when the gap is already this huge, they claim 20mm drop in the front but as per Farkle the drop might be lesser with Bilstein B8s Rear gap is not that bad, it's about 1.5".
245/45 along with Eibach springs would've definitely helped a little bit as the tires would've probably decreased the gap by 4-5 mm.

In the old days they would have already taken a chunk off of those springs with a hacksaw! 😀

[thatBimmerBloke]

Originally Posted by johnung

In the old days they would have already taken a chunk off of those springs with a hacksaw! 😀

haha, good old days Honestly 2 years back I'd have not even noticed the wheel gap, I was happy and content with my 328ix. As I started getting more involved I kept on finding all sorts of flaws. My girlfriend also played a part in this, she drives the Civic Type-R and has owned M235, Mini, Honda S2000 and a bunch of other cars before.

[Gen13 F36]

On the side note.... I have m-sport suspension (non EDC)...some days its sits with small wheel gap and there are days which it sit higher... WTF

[thatBimmerBloke]

Originally Posted by Gen13 F36

On the side note.... I have m-sport suspension (non EDC)...some days its sits with small wheel gap and there are days which it sit higher... WTF

Optical illusion or actual numbers? Bring out the measuring tape

[DriveS]

I have just fitted B6s with ACS springs. I have not taken measurements yet, but the rear has gone up higher than the front.


Here is my theory . Its mostly down to the piston forces differences in the shocks that are acting on suspension.

The Sachs shocks I removed had done 50K miles. On the rears there was virtually no return force of the pistons and fronts only a little more. The Sachs shocks were close to being gone. On my previous car I changed them at 60K and there were totally gone.
As the return force of the pistons on those shocks changed over time the car gradually lowered itself. So the car was lower than if it had new Sachs shocks in.

As the Bilstein piston force is significantly higher than a worn out Sachs, it will transmit more force onto the suspension, effectively reducing the spring compression and making the ride height higher.

I notice on my car that the change in height is more at the rear of the car. This is because the weight at the front of the car is greater due to the engine. However I do not know if the piston force is proportionally different between front and rear shocks in relation to the weight of the car above it. I expect it will be, but I also know that my front shocks can be fitted most F series x drive cars and mine will have the heaviest engine in (335d).
Hence why on my car the ride height has increased less on the front.

Evidence to support the theory -

1. Many posts on the internet about fitting uprated shocks and keeping the same springs
2. On my E92 the ride height changed when I fitted Koni shocks, which replaced totally shot Sachs
3. In the OP video, the theory about the spring is partially discounted as the rear shocks are not mounted in a strut with the spring.

I also think that B8s will not be any different to the B6 ride height if they have the same piston force when the spring is compressed. The height of the piston is the only difference and thats a red herring. However if they do indeed have a greater force when in the ride state compression, then this would change the height. But I expect it to be negligible.

[FaRKle!]

Originally Posted by DriveS

Here is my theory . Its mostly down to the piston forces differences in the shocks that are acting on suspension.

The Sachs shocks I removed had done 50K miles. On the rears there was virtually no return force of the pistons and fronts only a little more. The Sachs shocks were close to being gone. On my previous car I changed them at 60K and there were totally gone.
As the return force of the pistons on those shocks changed over time the car gradually lowered itself. So the car was lower than if it had new Sachs shocks in.

As the Bilstein piston force is significantly higher than a worn out Sachs, it will transmit more force onto the suspension, effectively reducing the spring compression and making the ride height higher.

If by "piston force" you refer to the forces the damper outputs when it's damping the spring, then unfortunately that's not the reason for ride height change. Those forces are created by the restriction of the piston moving through the fluid, and thus when the car is static, there is no force because the pistons aren't moving.

The "return force" you see when the piston shaft is extending out of the damper when it's out of the car is due to the gas pressure/gas force of the damper. I touched on that a bit where I mention how much higher the gas force of the monotube Bilsteins is compared to my OE dampers. A worn out damper that has had its gas charge leak out won't have the piston shaft extend out when taken out of the car.

You're correct that the spring orientation isn't the cause for rear ride height change, and I agree that there won't be a difference between B6 or B8 (unless your ride height is too low on the B6 such that the bump stop is being compressed at static height).

[KRS_SN]

i have b8 acs combo
rears were initially higher after installation than oem damper acs combo
now they have settled and look great ie back does settle over time and lowers.

[DriveS]

Originally Posted by FaRKle!

If by "piston force" you refer to the forces the damper outputs when it's damping the spring, then unfortunately that's not the reason for ride height change. Those forces are created by the restriction of the piston moving through the fluid, and thus when the car is static, there is no force because the pistons aren't moving.

The "return force" you see when the piston shaft is extending out of the damper when it's out of the car is due to the gas pressure/gas force of the damper. I touched on that a bit where I mention how much higher the gas force of the monotube Bilsteins is compared to my OE dampers. A worn out damper that has had its gas charge leak out won't have the piston shaft extend out when taken out of the car.

You're correct that the spring orientation isn't the cause for rear ride height change, and I agree that there won't be a difference between B6 or B8 (unless your ride height is too low on the B6 such that the bump stop is being compressed at static height).

Ok. There is no doubt that when out of the box the shocks will return to the extended position when compressed. In installation of rears I used a strap to hold the piston in the compressed position.
From what you are saying, if held at this position, the pressure in the tube will equalise after a period of time and the position will not extend back to the original position without being pulled. If this is the case, then I agree that piston force had nothing do do with ride height as there wont be any force after a certain period.

Is this what you are saying?