Modding chassis to CS-spec

[Racer20]

So I'm almost finished with my CS suspension conversion on my 2015 civic M3, and even without the correct rear bar (getting it installed in a couple weeks), my views on the CS package have changed a bit.

This suspension and calibration really does take even a base 2014 build M3 to the next level. The steering, ride, and handling feels like it has made up about 40-50% of the gap to a 911 but with only 10-15% of the loss in comfort, NVH, and usability. The quality of damping is better than any non-Porsche I've driven and may even suit my *personal* preferences better than a Porsche.

After a few days of driving, I can imagine that with all the rest of the updates that the CS includes, it really does add up to a special feeling car.

[EricSMG]

Originally Posted by Racer20

So I'm almost finished with my CS suspension conversion on my 2015 civic M3, and even without the correct rear bar (getting it installed in a couple weeks), my views on the CS package have changed a bit.

This suspension and calibration really does take even a base 2014 build M3 to the next level. The steering, ride, and handling feels like it has made up about 40-50% of the gap to a 911 but with only 10-15% of the loss in comfort, NVH, and usability. The quality of damping is better than any non-Porsche I've driven and may even suit my *personal* preferences better than a Porsche.

After a few days of driving, I can imagine that with all the rest of the updates that the CS includes, it really does add up to a special feeling car.

What differences exist between th ZCP suspension and CS suspension?

[nicknaz]

Originally Posted by Racer20

So I'm almost finished with my CS suspension conversion on my 2015 civic M3, and even without the correct rear bar (getting it installed in a couple weeks), my views on the CS package have changed a bit.

This suspension and calibration really does take even a base 2014 build M3 to the next level. The steering, ride, and handling feels like it has made up about 40-50% of the gap to a 911 but with only 10-15% of the loss in comfort, NVH, and usability. The quality of damping is better than any non-Porsche I've driven and may even suit my *personal* preferences better than a Porsche.

After a few days of driving, I can imagine that with all the rest of the updates that the CS includes, it really does add up to a special feeling car.

Thanks for sharing your input. I personally really value it since you work on that stuff for a living.

Can you share more about why you did the Cs suspension instead of going to aftermarket full coilovers?

[mechanic75]

Originally Posted by Racer20

So I'm almost finished with my CS suspension conversion on my 2015 civic M3, and even without the correct rear bar (getting it installed in a couple weeks), my views on the CS package have changed a bit.

This suspension and calibration really does take even a base 2014 build M3 to the next level. The steering, ride, and handling feels like it has made up about 40-50% of the gap to a 911 but with only 10-15% of the loss in comfort, NVH, and usability. The quality of damping is better than any non-Porsche I've driven and may even suit my *personal* preferences better than a Porsche.

After a few days of driving, I can imagine that with all the rest of the updates that the CS includes, it really does add up to a special feeling car.

Great stuff. What have you done so far? Will you get some cup 2’s at some stage too?

[CanAutM3]

Originally Posted by Racer20

So I'm almost finished with my CS suspension conversion on my 2015 civic M3, and even without the correct rear bar (getting it installed in a couple weeks), my views on the CS package have changed a bit.

This suspension and calibration really does take even a base 2014 build M3 to the next level. The steering, ride, and handling feels like it has made up about 40-50% of the gap to a 911 but with only 10-15% of the loss in comfort, NVH, and usability. The quality of damping is better than any non-Porsche I've driven and may even suit my *personal* preferences better than a Porsche.

After a few days of driving, I can imagine that with all the rest of the updates that the CS includes, it really does add up to a special feeling car.

A little piece of info that might be of interest to you, BMW recommends 35psi front and rear cold tire pressures on the CS with PSS. Slightly more than the 32psi recommended on base and competition variants.

[CanAutM3]

Originally Posted by EricSMG

What differences exist between th ZCP suspension and CS suspension?

They mixed and matched different components, like the rear CP swaybar paired with the standard swaybar and sunroof springs on the non-sunroof CS, if I recall correctly some examples.

[gatorfast]

Originally Posted by CanAutM3

A little piece of info that might be of interest to you, BMW recommends 35psi front and rear cold tire pressures on the CS with PSS. Slightly more than the 32psi recommended on base and competition variants.

Thats interesting, I wonder what prompted the increase in recommended pressure change.

[Racer20]

Originally Posted by EricSMG

What differences exist between th ZCP suspension and CS suspension?

As best as can be gleaned from ETK, The CS M3 uses the same springs and front bar as the base car. The M4 uses the full ZCP set up except the front bar.

[Racer20]

Originally Posted by CanAutM3

They mixed and matched different components, like the rear CP swaybar paired with the standard swaybar and sunroof springs on the non-sunroof CS, if I recall correctly some examples.

The reason this is done is that there is actually a "family" of springs for each vehicle rather than a single spring part number. If an M4 stripper used the same springs as a loaded exec pack sunroof M4, the heavy one would sit too low and the light one would sit too high. So they have several springs of the same rate that are each a few mm different in length to account for the different ride heights. As the car rolls down the production line, they choose which springs to use depending on the weight of the car. Each spring has a range of weights that it's designed for. e.g., for front weights between 1700-1750lbs gets spring A, 1750-1800lbs gets spring B, etc.

Most likely the M4 CS is lighter than any other F8X that has come before it, so they had to design a new spring that's shorter than the shortest one in the existing spring family, otherwise the car would sit too high.

[Remonster]

Originally Posted by EricSMG

Now the question is can I add the CS tune with 91 octane?

Yes you can, I used Bootmod3 to load the CS tune onto my M3 and ran it on 91 octane. Felt great and ultra responsive, I didn't get the feeling that it was being held back on the 91 octane. I'm not running the M4 GTS map on my car (obviously without the water injection) and it's even better, same bump in midrange torque as the CS tune but with a more potent top-end.

[Racer20]

Originally Posted by nicknaz

Thanks for sharing your input. I personally really value it since you work on that stuff for a living.

Can you share more about why you did the Cs suspension instead of going to aftermarket full coilovers?

Because I drive on shitty roads 80% of the time, and coil-over cars are not fun to drive on these roads. The ride frequency is too high on most of them and the car ends up following the uneveness of the roads too much. So my main priority was maintaining the adaptive function. OEM reliability and NVH is a benefit as well. Another benefit is that since I only get to the track 2-4 times per year, I don't like wasting time trying to dial in my setup at the track. This is basically an OEM setup with matched jounce bumpers and recommended ride heights, so I can trust that it'll be good out of the box.

I wasn't really on a mission to start modding my car, but by chance, I found a lightly used set that also came with some ZCP dampers from a member on here. This was intriguing because it met all my needs and would be only a rear bar away from the CS setup and just a front and rear bar away from the ZCP set up. Comparing these setups on the shock dyno and on my own car would allow me to gain some insight into BMW's tuning strategies. I was also hoping that the ZCP/CS dampers would have improved damping quality to reduce the impact crashiness on the bad roads I commute on (they do).

After installing this setup and testing the various EDC calibrations available, it became clear that the CS EDC cal had the damping quality that I was after and improved body control and front end bite quite a bit, and only needed a bit of extra rear roll stiffness to bring back the crispness of the initial steering response.

So I have an appointment on Tuesday to get the bar installed. (I do 90% of my own work, but the rear bar requires dropping the rear subframe and I want it done quick so I can enjoy the car before the weather turns bad).

I should also say that I had the ZCP cal coded in at first, and while it was good, it wasn't this good. When I loaded the CS EDC cal, the whole car came together and felt much more Porsche like. As CanAut said, even in comfort mode, you know you're driving a sports car.

I was surprised how different the roll vs. vertical balance was between the 3 EDC calibrations. I basically have base sway bars with ZCP/CS dampers right now. As such, the base EDC cal is quite well balanced with my base swaybars for roll, but commands too much damping from the ZCP shocks and isn't balanced vertically very well and rides poorly.

The ZCP cal matches my springs/dampers, so feels good vertically, but it's missing some low speed roll damping in the front and rear because it expects both bars to be stiffer.

The CS cal matches my springs, dampers and front bar, and as such, the front of the car is really well behaved in ride and roll. It's very well damped on bad roads and has a lot of bite in a corner. But the software expects less/slower roll from the rear so doesn't bring in enough roll damping to keep the car flat and make sure the rear follows the front without delay. As a result, the on-center steering and turn-in response isn't as crisp as the base set up.

Basically, I've found that you really need a fully matched setup to make any of these parts/calibrations really work for both road and track.

[Racer20]

Originally Posted by CanAutM3

A little piece of info that might be of interest to you, BMW recommends 35psi front and rear cold tire pressures on the CS with PSS. Slightly more than the 32psi recommended on base and competition variants.

That is quite interesting. I actually run 29psi cold because I find the impact harshness to be significantly better once the tires warm up. But I at least want to try to full OEM set up so I might play with tire pressures this weekend.

One thing I can't figure out is how to code the CS EPS calibration. The GTS comfort mode works pretty well with what I have now, but I suspect the CS set up is the best that BMW has to offer for the F80.

[Racer20]

Originally Posted by mechanic75

Great stuff. What have you done so far? Will you get some cup 2’s at some stage too?

See 2 posts up to see what I've done so far. I am not 100% sure what I'm going to do for wheels and tires. This whole adventure has basically been on a whim, and I have about half of a life to go on my PS4S. Ideally I'd pick up a set of OEM 763M's next spring with PSC2's for track duty, but I have a hard time stomaching spending that much on wheels.

[EricSMG]

Originally Posted by Remonster

Yes you can, I used Bootmod3 to load the CS tune onto my M3 and ran it on 91 octane. Felt great and ultra responsive, I didn't get the feeling that it was being held back on the 91 octane. I'm not running the M4 GTS map on my car (obviously without the water injection) and it's even better, same bump in midrange torque as the CS tune but with a more potent top-end.

Good stuff. I'm mostly interested in the top end - the ZCP car has the perfect midrange ramp up... it's just at the upper edge of what's controllable = perfect. But I would like a little more rip above 6.5k, more similar to the S65/S54 engines that I come from.

I'm also interested in more consistent WOT performance - less surge and lag.

Curious on your input here.

Originally Posted by Racer20

Because I drive on shitty roads 80% of the time, and coil-over cars are not fun to drive on these roads. The ride frequency is too high on most of them and the car ends up following the uneveness of the roads too much. So my main priority was maintaining the adaptive function. OEM reliability and NVH is a benefit as well.

We are totally on the same page here. I've jacked around with numerous suspension setups on the 36/46Ms over the last 15 years and always come back to OEM/plus setups as they offer by far the best overall road comfort. They're also easier to drive fast in the real world as the chassis stays much calmer, allowing me to drive and not react to changes in the road's surface.

Originally Posted by Racer20

That is quite interesting. I actually run 29psi cold because I find the impact harshness to be significantly better once the tires warm up.

Again, same page. I too run 29psi cold on the ZCP/666/OE PSS setup as this provides the best combination of steering response (still damn good) and impact harshness. Once you get into the low 30s cold the ride quality gets very bad very quickly.

[mechanic75]

Originally Posted by Racer20

That is quite interesting. I actually run 29psi cold because I find the impact harshness to be significantly better once the tires warm up. But I at least want to try to full OEM set up so I might play with tire pressures this weekend.

One thing I can't figure out is how to code the CS EPS calibration. The GTS comfort mode works pretty well with what I have now, but I suspect the CS set up is the best that BMW has to offer for the F80.

Loving your posts and feedback. Brilliant. I can help you with CS EPS coding... it’s the same setting as the GTS.. I checked it on my car out of interest.

[Racer20]

Originally Posted by mechanic75

Loving your posts and feedback. Brilliant. I can help you with CS EPS coding... it’s the same setting as the GTS.. I checked it on my car out of interest.

Thanks for confirming that! Good to know I'm not missing anything. I haven't quite figured the steering of this setup out yet. Surprisingly, comfort mode is the most responsive and natural feeling, as well as the lightest.

With my stock set up, M2 was sport+ everything, but I've changed it now to be sport+ engine and suspension with comfort steering.

I suspect that might change again once I have the correct rear bar installed (picking the car up Thursday).

[CanAutM3]

Originally Posted by Racer20

Thanks for confirming that! Good to know I'm not missing anything. I haven't quite figured the steering of this setup out yet. Surprisingly, comfort mode is the most responsive and natural feeling, as well as the lightest.

With my stock set up, M2 was sport+ everything, but I've changed it now to be sport+ engine and suspension with comfort steering.

I suspect that might change again once I have the correct rear bar installed (picking the car up Thursday).

On my 2015 M4, I also preferred the Comfort setting for the street. However, I found it too light and "wobbly" on track, which led to less precise steering inputs and therefore preferred the Sport+ setting.

On my M4cs, I still prefer the comfort setting for the street. I'll find out which one I like best on track this coming Monday.

[mechanic75]

Steering is one area where I think these cars let themselves down. No issues with how it steers just how it feels. Just off centre it has too much resistance for me, giving that rubbery feeling.

I don’t think the 19’s and cup 2’s help here but I’m not sure.

What do you guys think? Racer20 and CanAutM3.

[Racer20]

Originally Posted by mechanic75

Steering is one area where I think these cars let themselves down. No issues with how it steers just how it feels. Just off centre it has too much resistance for me, giving that rubbery feeling.

I don’t think the 19’s and cup 2’s help here but I’m not sure.

What do you guys think? Racer20 and CanAutM3.

I'm surprised they used the same EPS cal as the GTS. With just the springs, dampers, and EDC cal codes, It seemed like the effort and response was slightly mismatched just off center, but that was without the correct rear bar. I pick the car up Monday with the CS rear bar and a fresh alignment. I'll report back next week.

[CanAutM3]

Originally Posted by Racer20

I'm surprised they used the same EPS cal as the GTS. With just the springs, dampers, and EDC cal codes, It seemed like the effort and response was slightly mismatched just off center, but that was without the correct rear bar. I pick the car up Monday with the CS rear bar and a fresh alignment. I'll report back next week.

I am also surprised they would use the same EPS calibration as the GTS since the GTS has different front hub carriers with different offsets.

[Racer20]

Originally Posted by mechanic75

Steering is one area where I think these cars let themselves down. No issues with how it steers just how it feels. Just off centre it has too much resistance for me, giving that rubbery feeling.

I don’t think the 19’s and cup 2’s help here but I’m not sure.

What do you guys think? Racer20 and CanAutM3.

Picked the car up today with the correct CS rear bar and fresh alignment. The bar fixed the roll balance. The suspension balance of the car is quite good now. The steering . . . I'm not so sure about.

For most of the summer, I had the GTS EPS coded in along with my stock suspension. The GTS EPS has a pronounced U-shape to the effort curve . . . it's pretty light on center and builds up quickly off center as the tires load up and lat-g increases. The effort build matched the response of the tires and the rate of load transfer pretty good with this setup. I had no complaints about the steering feel or response.

The CS setup loads the tires and gets to a steady state attitude more quickly, and seems to change direction more quickly as well. The steering effort then needs to build quicker to match this behavior, but so far it doesn't seem to.

When the transient of corner entry is over and the car is leaning on its springs and bars, I want the steering to have the same feeling of taking a set, like I can "lean" against the torque on the wheel and it'll push back firmly and maintain the line. A stable equilibrium between my input torque and the wheel torque imparted by the tires and steering gear if you will. This gives the car a "crisp" response and a sense of solidity and confidence in a corner. I'm not sure this setup is 100% there yet.

I'm going to check the coding again and play with tire pressures a bit, I'll report back if I find anything interesting.

[melvyn]

Originally Posted by Racer20

Picked the car up today with the correct CS rear bar and fresh alignment. The bar fixed the roll balance. The suspension balance of the car is quite good now. The steering . . . I'm not so sure about.

For most of the summer, I had the GTS EPS coded in along with my stock suspension. The GTS EPS has a pronounced U-shape to the effort curve . . . it's pretty light on center and builds up quickly off center as the tires load up and lat-g increases. The effort build matched the response of the tires and the rate of load transfer pretty good with this setup. I had no complaints about the steering feel or response.

The CS setup loads the tires and gets to a steady state attitude more quickly, and seems to change direction more quickly as well. The steering effort then needs to build quicker to match this behavior, but so far it doesn't seem to.

When the transient of corner entry is over and the car is leaning on its springs and bars, I want the steering to have the same feeling of taking a set, like I can "lean" against the torque on the wheel and it'll push back firmly and maintain the line. A stable equilibrium between my input torque and the wheel torque imparted by the tires and steering gear if you will. This gives the car a "crisp" response and a sense of solidity and confidence in a corner. I'm not sure this setup is 100% there yet.

I'm going to check the coding again and play with tire pressures a bit, I'll report back if I find anything interesting.

Are you running 19s on front and 20s on rear