[Aeko]

I'm not exactly an expert at suspension or modifying cars but I have a very good idea of how I like a car to handle. My last car, an e46 M3 with B16's and running very similar tire sizes to the M2C, would break traction very gradually and communicate well when it was about to lose the rear when doing something like powering out of a sharp corner (u-turn, for example). I find that in cornering the M2C tends to kick the rear off pretty indiscriminately under power even with gentle throttle input. My goal is to make that transition between grip and sliding much more gradual.

In short, what can I do to help this?

In addition to this one of the first things I noticed is that the M2C tends to feel unsettled and the rear tends to feel like it's wiggling back and forth when coming out of a corner, even when the car is already straightened out and I get on the power late and gradually. Is this a result of the single diff mount and would a two mount brace help with this issue? It feels like it's winding the power back and forth between the left and right side even though the grip is there. I'm not sure if it's wheel hop or something happening with the suspension.

The M2C is currently all stock including wheels and tire sizes. PSS in factory spec, no suspension mods (though I am about to finish retrofitting OE EDC dampers, I already have electronics set up).

[ThreeStripes]

Consider a set of rear toe arms and an alignment before going after the differential.

I would also link up with Bimmer-Remote.com to see if you’re a candidate for coding the “CS” rear differential parameter. Not sure if some M2C builds got that parameter set from the factory or not but pretty sure they didn’t.

[Aeko]

Originally Posted by ThreeStripes

Consider a set of rear toe arms and an alignment before going after the differential.

I would also link up with Bimmer-Remote.com to see if you’re a candidate for coding the “CS” rear differential parameter. Not sure if some M2C builds got that parameter set from the factory or not but pretty sure they didn’t.

What am I looking to change in the rear, more toe in or out?

I have the car VO coded as a CS to make the EDC work. I don't think I flashed the GHAS but I'm pretty sure that is the only thing I need to do in order to make it function as a CS style diff.

[ThreeStripes]

Originally Posted by Aeko

What am I looking to change in the rear, more toe in or out?

I followed the lead of other more experience folks here and set my alignment to to .04 total toe in up front and .27 total toe in for the rear. It made a huge difference with stability under braking on track along with the spherical bushing on the solid toe arms. How much toe to run is personal preference up to a point though so keep that in mind.

Adjustable arms from SPL/BMW Motorsports/Fall-line, etc etc just make it easier to perfectly dial in toe and camber. Also, toe is less likely to slip with an eccentric lockout.

Originally Posted by Aeko

I have the car VO coded as a CS to make the EDC work. I don't think I flashed the GHAS but I'm pretty sure that is the only thing I need to do in order to make it function as a CS style diff.

If you can’t dig around and figure it out yourself pay someone to flip that parameter for you. Do the CS steering parameter and the CS MDM while you’re at it they’re definitely worth the hassle.

Finally, part of this may just be the huge difference in torque you’re not quite acclimated to coming from the E46? The PSS tires are great but fall of quickly and the car gets even more assy once they’ve got even 5-8k on em. PS4S seem to stick better with better manners for daily driving.

Good luck getting it dialed in.

[Aeko]

Originally Posted by ThreeStripes

If you can’t dig around and figure it out yourself pay someone to flip that parameter for you. Do the CS steering parameter and the CS MDM while you’re at it they’re definitely worth the hassle.

Finally, part of this may just be the huge difference in torque you’re not quite acclimated to coming from the E46? The PSS tires are great but fall of quickly and the car gets even more assy once they’ve got even 5-8k on em. PS4S seem to stick better with better manners for daily driving.

Thanks for all the input, this is really helpful!

Do you know offhand what the CS vs Comp coding does for the steering, diff, and MDM? I've heard supposedly the Euro CS MDM is less intrusive, though I didn't find the stock MDM all that bad IMO. I haven't found good info on what the improvements are just with changing the coding and I really don't get to drive the car hard enough to find out. I did some digging and I know where the options are now, just need to figure out how to do it in Esys instead of one of the apps like Protool. I'm confident in general with coding since I had to learn a lot to retrofit EDC, I just haven't bothered doing a lot of FDL coding.

Reading some other threads in people who came from the e46 M3 you may be right. I forget it probably had maybe half the wheel torque of the M2C, and it has so much of that down low. The M3 got totalled and I got the M2C two months later so I never got a back to back. In a straight line the M2C hooks so well it doesn't feel like it has THAT much torque, even compared to my e39 M5 with headers and a tune, which probably makes nearly 400 wheel hp and tq. Even the M5 doesn't feel like it crosses that limit as quickly.

The PSS rears on this car are from '22 and I've put 7k on it since I bought it, so maybe you're right about that as well. Both fronts are new. I was considering the PS4S but I really do not want to lose the turn-in feel the PSS have. I'm also looking at going to 18" using some custom brackets from another member for the 2NH as well as 380mm discs, so I'm debating putting PSS or PS4S on those when I get around to it.

[Aeko]

I checked with one of the Android apps and I already have the F87CS GHAS coding but I haven't really tested it since I did the EDC retrofit. For some reason it looks like the EPS might be set to F80 but I'll have to check in Esys once I feel like digging out my coding laptop and getting that all set up again.

Edit: Found a good thread talking about the GTS settings. So far nothing really on the CS settings, though: https://f87.bimmerpost.com/forums/sh....php?t=1643977

Also confirmed my M2C EPS is also set to F80 steering for some reason? I've never changed that value so I'm not sure why it would be that way. I did have BMW do "an update" when I first took it to the dealer for service but as far as I can tell it looks like they just did a software flash on some of the modules, the iStep was not updated. The biggest thing I noticed was the shift modes on the transmission changed pretty dramatically. In D3 it stays in gears way longer before shifting up if you're below 7k at a constant RPM, almost like an auto mode for track. Not sure if it would have changed then and somehow stuck even after I did the EDC retrofit (typschlussel to M2CS to get the car to talk to the VDC module). I would have thought that change would update it to F87CS like it did for the GHAS and VDC. I still need to check what the DSC is currently set to. Every single FDL setting on the car should be "factory" pretty much as I haven't changed a single one as the car currently sits.

[medphysdave]

Rear toe arms solved the wiggle for me. My guess is that going to a solid bushing in the control arms or adjustable control arms would help further.

Solid bushings in the front tension arms solved the front end wiggle under braking.

[Aeko]

Originally Posted by medphysdave

Rear toe arms solved the wiggle for me. My guess is that going to a solid bushing in the control arms or adjustable control arms would help further.

Solid bushings in the front tension arms solved the front end wiggle under braking.

Perfect, thank you! What specifically about the toe arms helped, solid bushings or just changing toe settings?

[ThreeStripes]

Both. Proper alignment sets it right. Spherical bushings eliminate deflection of rubber components ensuring the toe angle isn’t moving around.

It’s a weakness that gets exposed on track but in the street it’s not an issue because, laws and the whole social contract thing.

The diff bushing helps with traction too as I understand it but on the street it prevents wheel hop under hard straight line acceleration from a dig. All part of the puzzle but I would head there last.

[Aeko]

Originally Posted by ThreeStripes

Both. Proper alignment sets it right. Spherical bushings eliminate deflection of rubber components ensuring the toe angle isn’t moving around.

It’s a weakness that gets exposed on track but in the street it’s not an issue because, laws and the whole social contract thing.

The diff bushing helps with traction too as I understand it but on the street it prevents wheel hop under hard straight line acceleration from a dig. All part of the puzzle but I would head there last.

Noted. Any opinions on the Megan Racing toe arms? Looking specifically at sealed monoball since I'm mostly running this on the street.

[ThreeStripes]

Yeah, don’t get them.

https://www.bimmerworld.com/Suspensi...7-F80-F82.html

That’s the move. Just clean them every year or so and you’ll be fine.

[Aeko]

Got it, thanks!

[FaRKle!]

Originally Posted by ThreeStripes

Yeah, don’t get them.

Why? I've had Megan arms on my F31 for over 4yrs, been through a rear end accident with them (they held up fine), and haven't had any issues with contamination from lots of dirt/gravel road driving. The OEM for them is Hardrace. You'll still want a toe lockout kit with them.

[ThreeStripes]

Originally Posted by FaRKle!

Why? I've had Megan arms on my F31 for over 4yrs, been through a rear end accident with them (they held up fine), and haven't had any issues with contamination from lots of dirt/gravel road driving. The OEM for them is Hardrace. You'll still want a toe lockout kit with them.

Because it doesn’t include the lockout, and generally Megan products are not associated with quality.

OP if Farkle says they’re fine they’re fine. He be knowin.

Honestly I don’t think the rear toe arm is the root of this thread though. Stock bits should be fine for a car that only sees the street.

[Track/S]

Originally Posted by ThreeStripes

Because it doesn’t include the lockout, and generally Megan products are not associated with quality.

OP if Farkle says they’re fine they’re fine. He be knowin.

Honestly I don’t think the rear toe arm is the root of this thread though. Stock bits should be fine for a car that only sees the street.

The lockout is paranoid about some manufacturers, like the SPL garbage for example, they are not necessary, and if they were, BMW Motorsport would use them in their M4 GT4 or M2CSR.

Hardrace brand is for beginners.

[D.Yooras]

OP, the first thing to do for rear end stability is more negative camber. Factory rear camber (-1.8) is barely enough for a stock car, any modifications make this issue worse. Depending on how much front grip you have (coilovers, front sway bar, stickier tires, etc) you'll want at least (-2.2) in the rear before pursuing anything else.

When it comes to adjustable arms (toe arms in this case) when you change the length of the arm it changes the curve of the arm. So in this case, the toe arms change the toe curve whereas the rear eccentric adjusters only move the position of the arm which doesn't change the length or the toe curve.

Anytime I install, or adjust, adjustable lengths arms I benchmark them to make sure they are the same length, then adjust the eccentrics to fine tune static toe. If you do install adjustable arms, leave the stock eccentric bolts in place as they will give more of a tuning aid for dialing things in.

So short version, try additional rear camber first then it may be time to consider other options like adjustable arms, diff coding, or wider/stickier tires.

[Aeko]

Just an update on this: running the ZCP EDC dampers with the stock F87CS EDC tune and the car feels MUCH more planted. What you give up is having a bit more "float" and body sway, but the car doesn't feel like it has no idea where the rear is trying to go, it doesn't squirm under power, and the wheel hop is much reduced. I don't feel like the car is going to come unstuck when going over big undulations at speed any more and its far more confidence inspiring.

Next step is to go for adjustable sways to help with the roll. The EDC actually takes care of a lot of the pitch and dive in Sport+ but not the roll.