Ohlins R&T Spring/Sway Choice

[Obioban]

Obioban mentioned it earlier in this thread but 350 front 700 rear (or 6kg/338lbs & 13kg/728lb) will give you flat ride. And then a CSL front sway bar with stock rear will get you to around 69% FRC. I don't understand FRC enough to ELI5, but that spring and sway combo is what I'll be running when I order ohlins for myself.

That’ll be a bit oversteer biased at the limit, assuming you retain the rear sway.

[Tbonem3]

I think the 400lb front for Ohlins is too much for their 628 rear. I have that 628, but went with 343lb up front. Looks like they fixed it for E9x though - they went with 343/685lb. I think they should have come with 336/628lb by default for e46.

[cobra]

I think the 400lb front for Ohlins is too much for their 628 rear. I have that 628, but went with 343lb up front. Looks like they fixed it for E9x though - they went with 343/685lb. I think they should have come with 336/628lb by default for e46.

Why do you think the 400 in front is too high?

[9kracing]

I don't have any bounce or modulation with mine, and like I mentioned, mine feels WAY better than my old Dinan springs and Konis which are said to be "flat ride".

But, I'm also probably a tad lower than your average bear, which requires higher spring rates.

Also FWIW I have the Ohlins camber plates, 3DM spacers, and Hotchkis swaybars.

[T.J.]

I don't have any bounce or modulation with mine, and like I mentioned, mine feels WAY better than my old Dinan springs and Konis which are said to be "flat ride".

But, I'm also probably a tad lower than your average bear, which requires higher spring rates.

Also FWIW I have the Ohlins camber plates, 3DM spacers, and Hotchkis swaybars.

Good dampers are exponentially more important for ride quality than “flat ride”.

[Bry5on]

Obioban mentioned it earlier in this thread but 350 front 700 rear (or 6kg/338lbs & 13kg/728lb) will give you flat ride. And then a CSL front sway bar with stock rear will get you to around 69% FRC. I don't understand FRC enough to ELI5, but that spring and sway combo is what I'll be running when I order ohlins for myself.

This is a good target if you run OEM ride height. If you’re lowering the car (really, the front) then you’ll want to bring the FRC up because of how much the roll center drops in front when you lower the car. Geometrically, a ~66% FRC is neutral at OEM ride height. Neutral is hard for us humans, so a few percent higher will keep traction on corner exits. These numbers come from my own measurements and CAD models of the suspension geometry, everyone should feel free to recreate and verify! The math never lies

As much compliance as you can get away with will be fastest and most grip. Also, the net least disruption to the driver is likely to also be fastest, that’s the nature of pitch balanced ride frequencies. Flat ride is just a term coined by one dude to make this easier for people to understand, which is why it looks like its origin comes from fat cat motorsports.

[OldRanger]

Good dampers are exponentially more important for ride quality than “flat ride”.

Now that you mention that...I don't think I've seen any comments on Ohlins damper settings in this thread. Granted, Road and Track is a single adjuster, with a dual flow valve...so it's pretty simple...but it does work to alter the ride.

Based on what I understand: if you are increasing spring rates on your car (and changing "frequencies") you'll probably need to increase damping on an Ohlins R&T setup to handle higher rebound forces the spring generates. Unless for some reason you added weight to your car in the equation. On the other hand, controlling compression events with a combination of tire psi, damper settings, spring rates, swaybar stiffness, etc. with an approach that optimal for the track and available traction is a bit more complicated. So, it likely just boils down to "did that feel better?" or "was that faster?"

I'm still curious to learn what folks are setting the dampers at using the original Ohlins springs for track use - focusing on how you want the car to handle low (shaft) speed compression events.

[cobra]

This is a good target if you run OEM ride height. If you’re lowering the car (really, the front) then you’ll want to bring the FRC up because of how much the roll center drops in front when you lower the car. Geometrically, a ~66% FRC is neutral at OEM ride height. Neutral is hard for us humans, so a few percent higher will keep traction on corner exits. These numbers come from my own measurements and CAD models of the suspension geometry, everyone should feel free to recreate and verify! The math never lies

As much compliance as you can get away with will be fastest and most grip. Also, the net least disruption to the driver is likely to also be fastest, that’s the nature of pitch balanced ride frequencies. Flat ride is just a term coined by one dude to make this easier for people to understand, which is why it looks like its origin comes from fat cat motorsports.

I may have asked this before - but how does tire width play into the handling balance?

[freshprince2421]

Update on the Strohlins Kit. Barry confirmed that the E9x Ohlins front springs are a very close fit to the E46M3 Ohlins front damper. It seems like the rubber upper spring mount on the E46M3 stock strut mount will require a little trimming to get the spring seated properly. I have agreed to be the guinea pig. Bet my shop is going to love me for this.

Attached are two photos: (i) one depicting the slight interference of the rubber mount; and (ii) one without the rubber mount confirming the spring will fit once the rubber is trimmed away slightly/properly.

I will try to make time to run this to ground in the coming weeks and will revert. In the meantime, any thoughts, suggestions or ideas regarding the rubber mount are welcome and appreciated.

Any update on the e9x front springs as a better option?

[K-Dawg]

Sorry what I meant was your rear spring rate hz, not overall spring rate. IE 1.8 front, 2.0 rear

Everything I can find posted on the web traces back to this guy Shaikh, who owns Fat Cat Motorsports. Everything, on every single forum. BMW, Porsche, Miata. Every single one.

I'm not saying he doesn't know what he's talking about, because I've watched his videos, and he seems pretty knowledgeable.

But there's a ton of factors that go into your suspension besides spring rate, I'm not sold on generic "flat ride" spring rates for every E46 M3.

Try searches related to "pitch" instead of "flat ride."

[gaiakai]

This is a good target if you run OEM ride height. If you’re lowering the car (really, the front) then you’ll want to bring the FRC up because of how much the roll center drops in front when you lower the car. Geometrically, a ~66% FRC is neutral at OEM ride height. Neutral is hard for us humans, so a few percent higher will keep traction on corner exits. These numbers come from my own measurements and CAD models of the suspension geometry, everyone should feel free to recreate and verify! The math never lies

As much compliance as you can get away with will be fastest and most grip. Also, the net least disruption to the driver is likely to also be fastest, that’s the nature of pitch balanced ride frequencies. Flat ride is just a term coined by one dude to make this easier for people to understand, which is why it looks like its origin comes from fat cat motorsports.

How much more FRC% would you recommend targeting if I lower the car? Probably going to stick to 13.5" front 13" rear. If 66% is neutral at OEM height and the spreadsheet puts me at 69% with these spring rates and sway bar, should I be targeting somewhere around 72% FRC if I lower the car? Also does it matter if I'm switching over to a square setup?

[Bry5on]

How much more FRC% would you recommend targeting if I lower the car? Probably going to stick to 13.5" front 13" rear. If 66% is neutral at OEM height and the spreadsheet puts me at 69% with these spring rates and sway bar, should I be targeting somewhere around 72% FRC if I lower the car? Also does it matter if I'm switching over to a square setup?

Your best bet is other M guys with experience here or to run the math. I haven’t run the numbers on that setup exactly but a half inch is probably a 2% change, from memory. Based on some of the math I wrote up in my build thread, you can self calculate if you’re so motivated.

When I said 66% is balanced, I’d assumed square. Good call out

edit: I’ve had good luck around 69-69.5 at stock height, that’s what I run.

[Bry5on]

I may have asked this before - but how does tire width play into the handling balance?

I’m not modeling width on mine as I run square, but generally you’ll get more cornering traction out of a wider tire. For road feel, you want to manage your scrub radius and also width (not too wide) and tire blocks. The tire stuff is mostly above my pay grade, but actually the most important thing to optimize. Changing your width and offset can also change your track width, and therefore your handling balance and target FRC. That’s down in the details!

[Obioban]

66% is pretty… exciting.

IMO

I’m much happier with the car ~75%.

[LSB4Me]

Any update on the e9x front springs as a better option?

I have been preoccupied with other projects, but this is on my todo list.

My present intent is to make three changes at one time (probably in October at this point): (1) E9x front springs; (2) 3DM Ohlins front spacers (shop declined to install them the first time; I won’t take no for an answer this go-round); and (3) Hotchkis front sway bar.

There is an outside chance that I will install the springs alone for science, but I would like to put this behind me once and for all. If the brain trust here would like to hear how things go with just the springs, I could be persuaded.