[PureE92]

I put the tein springs on my car too cause I liked the rates but the drop was too low. I ended up going with the bmw performance springs but I went a little bit stiffer resulting in a higher sitting car. I can finally clear most driveways without scraping and the spring rates are pretty stiff. 176lb front and 530lb rear. It’s close enough to the tein and I’m happy.

[rvphuerta]

I have too much rake right now. I need to remove the rear height adjuster. It's a bit more work to try to get it right. That why I'm trying to put as much info on the height the spring give with measurements for the next person. I really thought the E30 upper springs perch would give more height than I got. I think that is what's lacking on most lowering spring info. I'm the type of person that needs measurements. I did like the spring rates on the Megan racing lowering springs for E90 M3. Obviously the front upper springs seat doesn't fit our spring perch. I do like them. I'll give a better review on the ride after 1000 miles and I get the correct height that I want.

[rvphuerta]

for E90/E91 Sport/Msport suspension: (measured from the bottom of the wheel(actual wheel and not tire) to the top of the arch on the fender; Obviously in the center.

Front Axle:
16" rim- 569mm
17" rim- 584mm
18" rim- 596mm / 23.46 inch / 13.71 inch
19" rim- 609mm

Rear Axle:
16" rim-550mm
17" rim-564mm
18" rim-577mm / 22.71 inch / 12.96 inch
19" rim-589mm

This is the OEM sport suspension measurements I found. Don't know how accurate it is. I think I would have been good with the eibach springs. I don't know the height on Eibach, not big on 2 finger gap measurement or lowers 1 inch. I prefer the measurement like the example above. What is the optimal suspension height? Can't seem to find the info. On the e46 is easy to find the info. On the E46 the lowest recommended height is 13.5 inch front and 13 inch rear. Reason the control arms are no longer parallel.

[mattanderson]

Mine is an E92 328i, so it's not quite apples to apples; but just for reference, here are my wheel-arch-to-bottom-of-wheel measurements on an 18" wheel:

Stock non-sport springs (C4 front, C1 rear)
Front: 24.75", 24.69" (L, R, respectively)
Rear: 23.88", 23.63"

Pro-Kit springs (p/n 2085.140)
Front: 23", 22.88"
Rear: 23", 22.88"

Pro-Kit with E30 strut mounts
Front: 23.5", 23.38"
Rear: 23", 22.88"

The E30 mounts gave me a solid half inch of travel by my measurements.

After 15k miles / 1 year of hard driving, it's settled another quarter inch or so all around.

[rvphuerta]

Thank for the information.

That's a decent drop from Eibach springs. I think I would have been good with Eibach, I do like my spring rates more. I'm at 22.875" in the front on both side, the height difference between left and right is negligible. I'm actually ok with the front that low. I don't have fenders liner issues and my front wheel tire is 18x9 +35 255/35r18.

[IamFODI]

FWIW, I don't think the "pitch" problem with aftermarket setups – particularly coilover kits from real suspension brands – is nearly as bad as it seems. Yes, they do raise ride frequencies much more in front than in the back – but that doesn't necessarily result in excess pitch when they're actually on the car.

On my E90 M3, I almost went for "flat ride" spring rates, but opted for an Öhlins kit with OTS spring rates. My calculated ride frequencies are something like 1.95 Hz front and 1.65 Hz rear.

Here's my actual lived experience with this setup: If there is any actual excess pitch, I can't tell. I thought there might have been at first, but after some miles and a big suspension bushing refresh, it seems to be gone.

How can that be?

One thing I've learned is that "flat ride" spring rates don't guarantee lower levels of pitch in the first place. Much less do they guarantee better ride quality or handling.

What they do is reduce the amount of damping needed to prevent excess pitch. This is attractive when you're designing a suspension setup from scratch because it can make your job easier when it's time to set up the dampers. Makes sense for an automaker, or for someone like Shaikh at FCM who is trying to optimize spring rates, damping, and anti-roll bars for specific applications. In theory, it can also reduce the overall level of damping needed, increasing compliance and thus grip (this doesn't always pan out in practice but it's a good thing to try for).

But a car with higher ride frequencies in front can still ride flatly with the right damping, and that's how good OTS setups are done. A coilover kit from a serious company like Bilstein or Öhlins will be damped well enough that you won't have to worry about pitch even if the spring rates are way off from "flat ride." It's also why some OE setups – like the E92 M3 GTS – can have non-"flat ride" spring rates from the factory.

If you think about this, it makes sense. As you said, OP, all the OTS coilover kits run higher ride frequencies in front. ALL of them, including the best. That alone should reassure us that the problem can't possibly as bad as it seems. Excess pitch isn't just uncomfortable; it's also unsafe, and suspension companies that have been in top-tier motorsports for decades aren't so stupid as to let it happen.

Yes, most aftermarket suspension setups do pitch excessively. But, to be completely frank... most aftermarket suspension setups suck. Suspension development is hard, and most companies – including many regarded as "good" – don't even try. The main problem isn't their spring rates; it's their lack of real development and optimization.

With Bilstein B8s, you probably have enough freedom to explore spring kits that don't have "flat ride" rates. B8s are very good dampers, and they will have been designed to account for typical aftermarket spring rates.

All this to say, "flat ride" spring rates probably can't hurt, all else equal – but don't let a lack of "flat ride" spring rates deter you from trying a kit that otherwise looks like it fits your criteria. If it was well developed, it'll be fine. You'd most likely be better off pursing depth of engineering and development than "flat ride" spring rates.