FCM E46 M3 Ride Harmonizer suspension spreadsheet - aka Flatride !!!

[duracellttu]

Side fun fact, the higher powered cars will have/require a higher FRC % to feel neutral and prevent on throttle oversteer.

Interesting, is there a target FRC based on rwhp ranges? I’m sitting at 340rwhp and trying to figure out my new setup specs.

[Radekxpl]

Other way. FRC % is front roll couple %, which is the % of overall roll cornering load transfer that is handled by the front suspension. If 100% were handled by the front, the car would plow and understeer, if 0% was handled by the front (100% by rear) this is "similar" to welded diff and oversteer/spin city.

I think neutral for our cars is around 75%, maybe a few % below that.

Right on the money 👍 Currently 74.4% feels just right

[newton22]

Ah thanks. Yes I misunderstood it.

Curious to know everyone's spring/sway setup. I personally am against the philosophy of sway bars in general because I like suspension articulation so I'm running stock sways and 500 front/600 rear Eibach springs. It sounds like I should drop down to the a ~300 spring rate front to go flat ride.

[Obioban]

The spreadsheet shows the CSL having a tiny front sway bar. Is that right?

Spread sheet has these values, which are accurate:



OD = outer diameter, which might be what you're thinking of as thickness. "The" is the wall thickness of the bar. CSL bar is hollow, to be lighter, but still stiffer than the M3 stock bar.

[newton22]

The spreadsheet shows the CSL having a tiny front sway bar. Is that right?

[mrgizmo04]

Side fun fact, the higher powered cars will have/require a higher FRC % to feel neutral and prevent on throttle oversteer.

[Obioban]

Other way. FRC % is front roll couple %, which is the % of overall roll cornering load transfer that is handled by the front suspension. If 100% were handled by the front, the car would plow and understeer, if 0% was handled by the front (100% by rear) this is "similar" to welded diff and oversteer/spin city.

I think neutral for our cars is around 75%, maybe a few % below that.

Derp, right!

[Tbonem3]

I would guess, though don't know without your corner weights and offsets, than you are not currently flat ride. But, I'm pretty sure you know this from the level of defensiveness in this post :P

Why would I say "sorta" if I were into this so much that I knew the bounce frequencies?

I thank Shak and this thread for putting me on the path to find the stock spring rates, moreso the ratio, and somewhat following his suggestions.

[mrgizmo04]

The Front roll couple is the oversteering/understeer ratio of the car. Higher is more oversteer biased, lower is more understeer biased.

Other way. FRC % is front roll couple %, which is the % of overall roll cornering load transfer that is handled by the front suspension. If 100% were handled by the front, the car would plow and understeer, if 0% was handled by the front (100% by rear) this is "similar" to welded diff and oversteer/spin city.

I think neutral for our cars is around 75%, maybe a few % below that.

[Obioban]

No idea, never got the spreadsheet to work properly and gave up. Based decision on others' findings and common sense. Knowing that stock rates are 143lb front and 385-650 (iirc) rear helped. Knowing that the popular 1:1 ratios like 550/550 or even 500/600 is for tracking (even tho most ppl's M aren't track cars) where you don't want diving, but can sacrifice comfort helped too.

I don't subscribe to the idea that there's only one, perfect choice when it comes to this stuff anyway. If the car feels good, and inspires confidence, then I'm happy. You can always tinker more. If you have the perfect setup, theres no more playing around and that's not fun! Theory is the key word.

The best thing I've done is to get away from Konis to Billys.

I would guess, though don't know without your corner weights and offsets, than you are not currently flat ride. But, I'm pretty sure you know this from the level of defensiveness in this post :P

[Obioban]

Fair point on springs

How is the front roll coupling calculated? What % should be targeted? Is it a combination of bounce freq and FRC that determine flat or pitched ride?

The Front roll couple is the oversteering/understeer ratio of the car. Higher is more oversteer biased, lower is more understeer biased. It's a function of sway bar stiffness and frequencies (so also your corner weights, offsets, etc), though I don't know the equation used to generate it off the top of my head. Where it should be depends on taste. Stock is 66-68%, CSL is 71%.

Flat ride is having the rear frequencies that are higher than the front frequencies. Higher frequencies recover from road events faster. The goal of flat ride is to have the rear of the car settle at the same time as the front, so you don't get into a pitch situation (which is basically where one of the car is recovered while the other is still dealing with the last impact). Exact flat ride can only exist at one speed, so there's not a magic ratio-- you choose the speed you want it to be spot, and then it works varying degrees of well around that (one of the inputs on the spreadsheet in the OP is speed, which will back calculate what flat ride ratio you need.

[duracellttu]

Shaikh just replied to my email and said he'll start posting on here soon.

Talking about spring rates kind of defeats the purpose of the spread sheet! The point of it is to target frequencies. Frequencies are influenced by spring rates, but also by wheel offsets, corner weights, unsprung mass, etc!

I'm currently at 1.92hz front, 2.06hz rear, with 4647 lb-ft/deg (off bump stop) of front roll stiffness and 1237 lb-ft/deg (off bump stop) of rear roll stiffness (vs 1688/809 off bump stop stock).

But, the springs and sways that got me there are unlikely to be the same as what would get you there.
(in 3071 lb car that's a bit front heavy and no longer has the counterbalancing battery on the passenger side, with my wheel offsets/sizes, 350 FL, 325 FR, 700 LR, 628 RR-- staggered left/right so I have equal frequencies left right)

Fair point on springs

How is the front roll coupling calculated? What % should be targeted? Is it a combination of bounce freq and FRC that determine flat or pitched ride?

[Tbonem3]

No idea, never got the spreadsheet to work properly and gave up. Based decision on others' findings and common sense. Knowing that stock rates are 143lb front and 385-650 (iirc) rear helped. Knowing that the popular 1:1 ratios like 550/550 or even 500/600 is for tracking (even tho most ppl's M aren't track cars) where you don't want diving, but can sacrifice comfort helped too.

I don't subscribe to the idea that there's only one, perfect choice when it comes to this stuff anyway. If the car feels good, and inspires confidence, then I'm happy. You can always tinker more. If you have the perfect setup, theres no more playing around and that's not fun! Theory is the key word.

The best thing I've done is to get away from Konis to Billys.

[Obioban]

"Sorta" flat ride checking in. Increased front bar, stock rear. 325lb front 550lb rear. 13.5/13.25"

Much better than the 440lb/550lb stock sways I used to run!

What is that in hz with your corner weights?

[Tbonem3]

"Sorta" flat ride checking in. Increased front bar, stock rear. 325lb front 550lb rear. 13.5/13.25"

Much better than the 440lb/550lb stock sways I used to run!