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      06-24-2019, 06:04 PM   #221
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Quote:
Originally Posted by wyatth View Post
Interesting, 21K on the shocks is not much at all and I can't imagine they wear so much just sitting there. Also surprised your PO put Dinan springs on a ZCP car - that's known to drop the car like, a few MMs at most. Eibach, ZCP, and Dinan springs are all quite close in rates/height.
Thereís more to life than the drop, I guess. Maybe Dinan springs give a little bit better handling? I got them for ďfreeĒ so Iím not going to complain.

Iím not saying the shocks are worn, but Iíve noticed quite a difference in control since I brought the car here last year. Perhaps the bushings didnít do well in the humidity, perhaps the dampers just havenít liked sitting. I figure I have to start fixing things somewhere, might as well start with Bilstein, since they apparently work as good or better than stock.

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Originally Posted by wyatth View Post
FWIW you have Dinan Stage 1 suspension. Stage 2 adds the sway bar, 3 adds the camber plates (or vise versa).
Some other guy told me different last year:

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Originally Posted by wyatth View Post
^ Thatís right, minus the dampeners (just springs and mounts/stops). And stage 3 adds the front sway.


Regardless, the car has Dinan Stg 2. Thatís what his build sheet says. Sway bar looked stock when I crawled under the car.
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      06-26-2019, 07:18 PM   #222
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Lol, what an idiot that guy was!
Assuming no misunderstanding or other context.
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      06-26-2019, 08:56 PM   #223
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      08-06-2019, 05:53 PM   #224
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I read through this whole post and has great info. My E90 M3 with competition package has about 30K miles. Shocks should still be good but noticed the lowering at the front like all have said happens. I have biltsteins on my M coupe and they are great.

From the posts it looks like the B6 raises the front when you use with stock springs. If you go with fresh OEM shocks shouldn't we get some type of raising of the front end as well? Just not as much?

Trying to make a decision which way to go. Also for shocks this is the first time i have seen shocks wear out so early as well.
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      08-06-2019, 06:07 PM   #225
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I certainly hope the ZCP suspension lasts more than 30k miles
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      08-08-2019, 07:15 PM   #226
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Me too. I'm at 50K and really curious how long they'll last so that I can plan other suspension work. Also still curious how the height of Bilstein B6 + ZCP springs compares to OE ZCP setup ... funny how this is all still speculated!

Ansel, good to see you on here, I enjoy your IG account. But you have a superfluous "Cayman" in your signature.
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      08-09-2019, 01:18 AM   #227
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Curious, do the B6s also work with KW HAS or the Dinan coilover conversion kits?

I suppose that's entirely dependent on if the B6 and EDC shocks are the exact same diameter at the point of where the sleeve is installed.
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      08-13-2019, 04:40 AM   #228
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Quote:
Originally Posted by 6ixSpd View Post
Curious, do the B6s also work with KW HAS or the Dinan coilover conversion kits?

I suppose that's entirely dependent on IG the B6 and O EDC shocks are the exact same diameter at the point of where the sleeve is installed.
I'm curious about this too. I'm also looking to change my setup and this crossed my mind. I currently have stock
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      08-14-2019, 08:49 AM   #229
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Quote:
Originally Posted by wyatth View Post
Me too. I'm at 50K and really curious how long they'll last so that I can plan other suspension work. Also still curious how the height of Bilstein B6 + ZCP springs compares to OE ZCP setup ... funny how this is all still speculated!

Ansel, good to see you on here, I enjoy your IG account. But you have a superfluous "Cayman" in your signature.
I am same as you but starting to notice the dampening is not as good even at 30K miles. I would like a drop in option if the ride height is same as stock. If don't have any low mileage stock ZCP, I don't mind ordering another set of oem dampers and then measuring.

Thanks for spotting my typo!
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      10-13-2019, 07:08 PM   #230
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Quote:
Originally Posted by MidLifeM3 View Post
At this age of our M3s, many E9x owners will be looking for replacements of worn out stock shocks and for those of us who like to keep our EDC functionality I'm sure this thread and the related ones on B16 coilovers will be visited a lot. Although prices on OEM replacements seem to be coming down, still there will be interest in these Bilstein as an alternative to OEM. Certainly for me I was drawn to these because of Bilstein reputation as a quality shock and to address what I felt was a bit loose rebound damping on the stock EDC shocks. So all well and good ....

one question that comes up over and over an over in threads about the B6 is "will it raise my car?", followed by "how much?" Since I just went through my own analysis to try to quantify that effect, I thought for public service to the community I would share so others could have an idea what to expect.

For many on this forum the following may be obviously apparent but I'll start with the basics. All shock abosrbers, at least when new, are pressurized to suppress foaming and cavitation of the shock oil. Twin tube shocks like the OEM ones are commonly pressurized to about 100psi, while monotube shocks like the Bilsteins use a higher pressure around 300psi. As you'd expect intuitively, that pressure tends to force the shaft out of the shock body, and when installed that force will push up on the car tending to lift it slightly. But how much is that force? We need to know the relevant area to convert the psi to absolute force.

if you consider the inside of the shock, the piston (with the shaft attached to it) is sitting there inside this pressurized tube. But, the pressure is hydrostatic and because the piston has holes through it the pressure is the sameabove and below the piston. That pressure on both sides almost balances.... except for where the shaft attaches to the piston. Below the piston, the pressure pushes up on the piston surface everywhere, but above the piston the pressure can only push down on the exposed parts of the piston that are not covered by the shaft. The net force exerted on the shaft is simply the pressure in the shock times the cross-sectional area of the shaft.

For the Bilstein "inverted monotube" design note that the huge-looking cylinder sticking out of the yellow housing is not the shaft. That's the main tube, the shaft sticks out the bottom of that and is hidden inside the housing. On the stock OEM shocks (and all twin-tube shocks) in the conventional "right side up" configuration the shaft sticks out the top.

Though I haven't received my B6 yet (that pesky back order) I believe the shaft on these is 14mm. So the cross sectional area is about 0.24 sq in. Then the force exerted by 300psi is 300*0.24 = 71 lbs.

For the OEM twin-tube shocks assuming a typical 100psi pressure, the force exerted would be about 1/3 as much, roughly 24 lbs.

And for all those of us with 90k miles on our shocks, chances are good that some or most of that 100psi has leaked out by now so the force might be pretty limp. If when you remove your old shocks the shafts don't extend (even slowly) then you didn't have much pressure left inside....

On the front axle the shock and spring both have a motion ratio close to 1, and the stock front springs are about 160 lb/inch rate. compared to a fresh stock setup, the Bilstein will be pushing up with 71-24 = 46lbs more force.
46lbs / 160 lb/in = 0.3 inches, about 7mm

Compared to worn out OEM shocks with little to no pressure remaining, the delta will be larger, around 0.4" or 10-11mm.

In the rear its slightly more complex because the motion ratios are far from 1 but this is the reason why users report less lift at the rear than at the front when installing Bilsteins. The force exerted on the shock shaft is still the same, that's just determined by shaft diameter and pressure. So 70lbs or so on Bilstein, 24lbs or so on fresh OEM. The spring rate is 550lb/in, with a motion ratio of about 0.58 relative to the wheel. The shock is not concentric with the spring and has a different motion ratio - roughly 0.8 (though I admit I could get this more precise with more careful tape measure work - but close enough for this purpose). Converting both to wheel rate makes the math more intuitive
550lb/in * (0.58)^2 = 185 lbs / inch spring wheel rate
46lbs * 0.8 = 37lbs more wheel-equivalent force from the shock

Then the 37lbs wheel-equivalent more force exerted on the shaft of Bilstein vs fresh OEM results in 37/185 = 0.2" higher ride height at the rear. If your reference point is fully deflated shocks then the relative rise will be up to ~0.3" higher than your very tired worn out shocks. In either case only a little more than half as much effect at the rear as at the front.

Since Lutfy has kindly provided a rather precise description of his case we can use his experience to assess and validate these calculations. He started with a non-ZCP car and added Bilstein B6 plus Eibach springs and ended up at nearly identical to ZCP height. ZCP is 10mm or 0.4" lower than non-ZCP. the Eibachs are supposed to give 0.8" drop in front and 0.6" in rear. The B6 would counter that with 0.3" rise in front and 0.2" in rear. Net result, 0.5" drop front and 0.4" drop rear, spot on to a ZCP.

For those who use B6 with stiffer springs like the Swift, the effect of the "bilstein lift" will be a little less in proportion to the additional spring rate. The bilstein will push up by the same 70 lbs, but your sport springs with higher rate will extend a little less in response.

All of this only matters with the non-adjustable spring perches, since the coilover or sleeve-over guys can just dial up or down to whatever static ride height they want. Since unfortunately the B6 is not compatible with the sleeve-overs that trick won't work for those of us considering these shocks. If we don't like the impact on ride height our only option is to change to different springs. Or to go for the B16 coilover kit. This is purely a cosmetics question, those few 1/10's inch change in ride height will have no deleterious effect on handling, but replacing floaty worn out shocks with fresh ones will certainly be a positive improvement.

I've also seen questions of whether the high pressure shock increases the spring rate. Technically yes but the effect is smaller than the impact on ride height. The effective spring rate is due to the additional volume displaced by the shaft as it moves down into the tube, which further compresses the gas raising its pressure. The increase in pressure per inch of shaft insertion, multiplied by the 0.24 sq in of shaft cross section, is the effective spring rate due to the shock. To calculate it exactly we'd need to know the actual volume of the gas chamber which I do not have easily on hand. But considering the shaft cross-section is pretty small relative to the piston or tube cross-section this added spring rate should be fairly insignificant.

Hope this is helpful to all those out there searching the threads and wondering about the effect on ride height.

For my case, my plan is to go for the B6 along with Dinan springs (0.5" drop) and recover back to about my current ride height on well-worn OEM shocks. Otherwise the B6 look like a good match to any of the mild lowering springs out there like Eibach.


I have not seen any quantitative data on the length of the internal bumpstop of the B6 (my inquiries to Eibach have not been responded to). Nor have I seen anyone publish shock dyno results on these or OEM. I guess the guys who dyno their shocks are all focused on race shocks. But it would sure be nice for the engineering-minded to have some mroe quantitative comparisons of these aftermarket parts so we'd know ahead of time what we're getting into. Though the Bilsteins are slightly easier on the wallet than OEM, you're still looking at close to $1800 for the set of four plus labor (or an afternoon of your own time if youre the DIY type) so its not an insignificant investment to "try out and see if you like it". And the qualitative reviews are great but one guy's plush ride is another's buckboard; one guy's taut control is another's flabby boat. Pretty hard to translate to our individual expectations. If anyone out there has measurements of the bump stops, or shock dyno data on these B6, I would love to see it!

I also wonder if anyone has weighed the unsprung weight of B6 vs OEM. The B6 steel shock overall is much heavier, but since its the inverted design some of the extra weight will be sprung weight and in increased unsprung weight might not be so much worse than stock.
Fantastic post and super informative. Thank you!!!
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