[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...

On my E90 M3, I almost went for "flat ride" spring rates, but ended up going for an Öhlins kit with OTS spring rates. My calculated ride frequencies are something like 1.95 Hz front and 1.65 Hz rear. Definitely not "flat ride."

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, there seems to be none.

How can that be?

One thing I've learned is that, when we talk about "flat ride" spring rates reducing pitch, that's only about what would happen without dampers. Once dampers are in the picture, it's much more complicated, so we can't just say a setup with "flat ride" spring rates will necessarily pitch less / ride better / handle better than one without. You have to consider the system.

"Flat ride" spring rates 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. Also makes sense for someone like Shaikh at FCM (the guy who popularized this in the first place), who optimizes spring rates, damping, and anti-roll bars all together for each individual car. In theory, "flat ride" spring rates might 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 without excess pitch.

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 potentially unsafe, so 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. Not an issue if you buy from a real suspension company – one that does real development for each application instead of cranking out as many different kits as possible.

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 them deter you from trying a kit that otherwise seems to fit your criteria. As long as your springs and dampers were well developed, you'll be fine. You'd most likely be better off pursing depth of engineering and development rather than trying to make the ride frequencies conform to a single rule of thumb.

[rvphuerta]

Originally Posted by IamFODI

FWIW...

On my E90 M3, I almost went for "flat ride" spring rates, but ended up going for an Öhlins kit with OTS spring rates. My calculated ride frequencies are something like 1.95 Hz front and 1.65 Hz rear. Definitely not "flat ride."

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, there seems to be none.

How can that be?

One thing I've learned is that, when we talk about "flat ride" spring rates reducing pitch, that's only about what would happen without dampers. Once dampers are in the picture, it's much more complicated, so we can't just say a setup with "flat ride" spring rates will necessarily pitch less / ride better / handle better than one without. You have to consider the system.

"Flat ride" spring rates 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. Also makes sense for someone like Shaikh at FCM (the guy who popularized this in the first place), who optimizes spring rates, damping, and anti-roll bars all together for each individual car. In theory, "flat ride" spring rates might 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 without excess pitch.

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 potentially unsafe, so 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. Not an issue if you buy from a real suspension company – one that does real development for each application instead of cranking out as many different kits as possible.

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 them deter you from trying a kit that otherwise seems to fit your criteria. As long as your springs and dampers were well developed, you'll be fine. You'd most likely be better off pursing depth of engineering and development rather than trying to make the ride frequencies conform to a single rule of thumb.

I'll will go with FMC later. I already have springs rates in mind. Suspension is subjective. I would never get BC coilovers but some do and have good reviews. I actually have some entry level coilovers for my E46. I only got them because it came with Eibach springs. It was by accident that the spring rates came with flat ride. I don't believe it was by designed. For the price I could not pass on the opportunity to test them out. I was actually surprised how good they ride on the street. It's comfortable and complaint for the wife. That's the real test, wife approved. My frequency are around 2.04 hz front and 2.26 hz rear. I was debating between Ground Control, TC Kline and Fortune Auto. Ground Control never got back to my on my question. TC Kline is nice since I can buy just the damper by themselves, but I want to keep the spring rates I have and the rear won't handle my spring rate. Fortune Auto would be nice if they can just sell the damper with no springs. I went with YCW coilovers. Bought them right after the budget coilover. I will see how it compares to YCW the only difference is going to be damper. I haven't taken a ride on car with pitch coilover. On my SRT4 the ST coilover have flat ride. On 95 civic i had 336 front and 250 rear which is flat ride. I remember driving my 99 Civic with 448 front and 448 rear and that flat ride but the rear is too stiff compared to front. I was a bit harsh high speed and dips. The people in the rear seat would bounce and hit their head. I want to try a pitch setup to see how it feels on my E46 with OTS springs all coilover have 8kg from and 10kg rear. My front damper can handle the spring rates but the rear spring will be to soft for the damper. The wife drives the E90 while I drive the E46. FCM has good information on educating people. What I like is that he put his theory to the test. It sucks that he doesn't offer stage one anymore, it was just valve correct with the ride nitrogen pressure. I notice that BMW community are more knowledgeable in Flat Ride and suspension frequency.

Side note.
My entry level coilover also offer strut and shock for lowering springs. I asked if the dampers can handle the 200lb front spring rate. Respond was yes. Will be trying those as well. I'll have to figure out the rear since I have E90 M3 rear shocks, no option available. I wonder if the F30 rear damper will fit, looks like it will.

[IamFODI]

Originally Posted by rvphuerta

My frequency are around 2.04 hz front and 2.26 hz rear.

Wow. That rear rate... Are you sure? On my calcs, 2.26 Hz in the rear would need a ~1300 lb/in spring. That's.... really really stiff.

[rvphuerta]

Originally Posted by IamFODI

Wow. That rear rate... Are you sure? On my calcs, 2.26 Hz in the rear would need a ~1300 lb/in spring. That's.... really really stiff.

That's on a E46 not E90, it's a 150 n/mm or 857 lb/in. Do E90 need reinforcement on the rear like E46 for a true coilover.

[IamFODI]

Originally Posted by rvphuerta

That's on a E46 not E90, it's a 150 n/mm or 857 lb/in.

Ah, okay.

Originally Posted by rvphuerta

Do E90 need reinforcement on the rear like E46 for a true coilover.

Depends how long you want to drive before something breaks.

[rvphuerta]

Originally Posted by IamFODI

Ah, okay.


Depends how long you want to drive before something breaks.

Just wondering. I remember reading that it will feel softer using a true coilover vs divorce at the same frequency don't know how true the statement is.

Example

I have a rear 857lb, it gives me 2.26 hz. Now on a true coilover 380lb springs would give me the same frequency as 857lb. Even though it's the same frequency it should feel softer because of the lower springs rate.

[rvphuerta]

Got a response back from Tein about bump stops. It says to cut the bump stops 1.3 inch. Unfortunately on our inverted damper it's more difficult. The OEM sport bump stop is 2.75 inch long, taking 1.3 inch will leave you with 1.45 inch long or 36.83 mm. Which is what I wanted to cut or get a bump stop from 5x racing in that length.

[IamFODI]

Originally Posted by rvphuerta

Just wondering. I remember reading that it will feel softer using a true coilover vs divorce at the same frequency don't know how true the statement is.

Example

I have a rear 857lb, it gives me 2.26 hz. Now on a true coilover 380lb would be my new spring rate. Even though it's the same frequency it should feel softer because of the lower springs rate.

I don't see how that's physically possible. Feel comes from frequency and damping.

Maybe the person saying that got their calcs wrong and actually had a lower frequency with the true coilover than they thought. Or maybe there was some other variable in the mix for them, e.g. damping was different between their divorced and coilover setups. Or maybe they're just flat-out mistaken.

[rvphuerta]

Originally Posted by IamFODI

I don't see how that's physically possible. Feel comes from frequency and damping.

Maybe the person saying that got their calcs wrong and actually had a lower frequency with the true coilover than they thought. Or maybe there was some other variable in the mix for them, e.g. damping was different between their divorced and coilover setups. Or maybe they're just flat-out mistaken.

I fixed the sentence. It didn't make sense. I don't know have accurate that would be would be. I think if was on a mustang too. I was just wondering.