Suspension frustrations

[huskcummerbund]

So, the previous owner lowered this Z3 but never retained any information about exactly what parts were used or how much it was actually lowered. But I know that it is too low. Going off the Bentley book, "normally loaded" on 17's the stock regular and sport ride height should be 660-675mm in the front and 578-593mm in the rear. Instead, I've got about 560-565 all the way around, and that's unloaded so the measurement would be even lower if I happened to have two sets of 68kg weights an another of 21kg to measure it properly (Seriously, BMW... wth?). So, by my admittedly dubious Oklahoma education system math, that's a >100-120mm drop from the Sport suspension, right? That's a lot.

I can tell that it has a full Billstein B8 system, though I'm not sure which springs were installed. So, I decided to swap the springs all the way around with these: https://www.turnermotorsport.com/p-4154-z3-19-hr-sport-spring-set/

Product Details
Front Lowering -1.5"
Rear Lowering -1.25"

Of course, they don't specify if it's expecting ~30-37mm from Standard or Sport but, if I had to guess, it would be from Standard, which would be roughly double the Sport drop. Either way, that should, in theory, lift the car more than 70mm all the way around, no? Well... it didn't. I may have gained about 5mm now that I've driven it and everything has settled in.

As far as I can tell, it's got a normal set of Bilstein B8 struts and shocks, so I don't understand where I'm missing roughly 75mm of ride height or how to, umm, get some or all of it back. I've read that one can replace the lower spring perches in the rear (I've got 7.5mm installed) with thicker ones, or even stack a couple of them, so I might be able to add ~25mm to the rear. No idea how I would do something similar to the front. Or I could probably replace the aftermarket springs with OEM springs (which opens a whole new nightmare of ordering parts off Ebay). But I suspect even then it would still be significantly lower than stock.

Thoughts? What could I be missing?

 

[AntStark]

Are they the correct B8s for a Z3? ..check the serial numbers against the bilstein web site

 

[huskcummerbund]

Are they the correct B8s for a Z3? ..check the serial numbers against the bilstein web site

I'll have to check again when I get home. Last time I looked, Bilstein's website was a real PITA to use. But, I suspect so since the rear is just a spring and a shock, and I know the new springs I bought are correct, according to the manufacturer, yet provided only a few millimeters of lift.

 

[Peewee]

Your measurement at the rear of around 561mm seem about right for 32mm lowering springs. Your measurement at the front should be around 637mm with 38mm lowering springs. Not exact because the BMW height specification is for a loaded vehicle.
Are you sure you are measuring the front height correctly? - from bottom edge of wheel rim to the top of the wheel arch (the black plastic liner).

 

[huskcummerbund]

Your measurement at the rear of around 561mm seem about right for 32mm lowering springs. Your measurement at the front should be around 637mm with 38mm lowering springs. Not exact because the BMW height specification is for a loaded vehicle.
Are you sure you are measuring the front height correctly? - from bottom edge of wheel rim to the top of the wheel arch (the black plastic liner).

I believe I'm measuring, and converting to metric, correctly. Also, if I was able to load the car correctly for the measurement or if BMW wasn't stupid and provided the unloaded ride height instead, the difference would be even greater. And greater still with my 95kg in the driver's seat rather than the prescribed weight.

I'm just now realizing the rear really isn't that far off and yeah, replacing the spring pads would probably be plenty good. Again, I cite my Oklahoma education and also fewer than the recommended hours of sleep. A stacked pair of 15's would give me about 22mm extra in the rear, and that would probably be sufficient.

Unfortunately, the front is still 100mm down and that's a problem in two ways, 1) figuring out why and how to fix it correctly so that I stop scraping the spike strip when I'm leaving work and, 2) since it sits dead level right now, if I were to add 50-75mm back into the front somehow it would be noticeably higher than the rear, even with the rear lifted as described above. I'd also have to readjust the headlights again... But that's easy.

Also, it's been kind of difficult to find any OEM-height springs that haven't been flogged for 150,000km+ already or less than brand new BMW OEM part for a nearly 30 year old car prices. Even the used parts are a bit expensive for an experiment.

 

[Peewee]

100mm (4 inches) is huge and will be clearly noticeable - the car wouldn't sit dead level at all and the wheels would likely hit the bodywork when you turned a corner.
Attached is how you should be measuring the front.
I have sport suspension which is 15mm lower than standard and even so I have to be VERY careful going over speed humps to avoid grinding the underneath.
If ground clearance is an issue for you, suggest swapping your H&R lowering springs for standard ones.

 

[huskcummerbund]

WTH? I'm measuring from the top of the actual wheel arch, but that is not how I would describe that photo. And, if that somehow is the right way to measure... How the hell do you measure that in the rear? Now I'm even more confused.

Also, there is visible damage to the inner guards up front from being so low. So, yeah, it's low.

 

[Peewee]

Yes, the rear measurement method is different. That's the way BMW specify it, so hopefully you are less confused now.

 

[huskcummerbund]

BMW engineers would climb over an entire mountain of hot and horny virgins just to f@#$ a technician...

Of all the asinine things I've learned about this car since I bought it, this is... among them. I'll re-measure when I get home. Pretty sure it's still going to be pretty low.

 

[Stevo7682]

Most lowering springs that you see for zed 3 in uk are generally 30mm drop
from standard height ( factory sports springs 15mm drop)
This drops zeds by a fair bit ( exaggerated by worn rear spring pads)
It all depends on what you want to do with your zed and what your prepared to sacrifice.
Lowering a zed will make it more focused on the back roads but ruins its town ride .
For me personally we tour round a fair bit of Scotland and Northern England at times so our zeds are on stock height springs, sachs shocks, solid rubber front arm rear bushes replacement drop links etc and i like the way that drives
Yes fair enough a lowered stiffened zed would take me on a bend but i sacrifice that for a bit more comfort so like i said depends what you want .
You can keep the lowering springs pud new thicker pads in and you will gain a few extra mm.
Stephen.

 

[huskcummerbund]

100mm (4 inches) is huge and will be clearly noticeable - the car wouldn't sit dead level at all and the wheels would likely hit the bodywork when you turned a corner.
Attached is how you should be measuring the front.
I have sport suspension which is 15mm lower than standard and even so I have to be VERY careful going over speed humps to avoid grinding the underneath.
If ground clearance is an issue for you, suggest swapping your H&R lowering springs for standard ones.

So, measuring by the method illustrated in the photo... which I contend has to be high on the list of Stupidest Ways to Measure Ride Height and directly contradicts the text description of method in the Bentley manual and possibly that of the book the scan was taken from (can't tell for sure, it's incomplete), the unloaded ride height in the front is currently ~645mm (25 3/8in). I was able to find about 150lbs of crap to load in the driver's seat, but not enough for the rest, but the difference at the front-left was only ~4-5mm. If that's accurate, and it might be since now it's within the realm of reason, then I'm only actually down about 30mm from standard and roughly on target for what you expected.

So, I guess I need to get standard height springs. Which leads to the next question... which springs are those? Apparently there are 3 part numbers to choose from and I can't find any specifications for any of the three, or specifications for the aftermarket springs intended to replace any of the three part numbers.

 

[Peewee]

If it helps, odd numbers are for the left hand side (drivers side for you) and even numbers are for the right hand side. Of course they are identical, but that's how BMW list them.
Suggest you contact your local BMW dealer to get part numbers for your particular car. BMW have (or used to have) a spring configurator which matches springs depending on the specification (weight) i.e. engine size, manual/auto (i.e. suffix 655,656/653,654), air conditioning or not. I don't think it makes that much difference to ride height, but again, that's how BMW do it. They will need your VIN number to help.
These appear to be from a 1.9 auto and may be worth a look:-

https://www.ebay.co.uk/itm/166091703546?chn=ps&_ul=GB&mkevt=1&mkcid=28&google_free_listing_action=view_item

.
Reverting to standard springs with B8 struts needs consideration though unless you plan to change these back to standard as well. There may be others on here who can advise.