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

[mrgizmo04]

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

[newton22]

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

[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]

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.

[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

[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.

[mrgizmo04]

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.

Flat ride is more of a concept between front and rear axle based on frequencies to have the car settle evenly after going over a bump at a certain speed. Yes you will need to either drop the front rate, up the rear, or both.

If you do that, you will have a much tighter rear end (😉), and oversteer prone chassis, which you will have to counter with bigger front bar.

[mrgizmo04]

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

That comment was more generalized to different chassis, like Miatas are probably around 60%, s2000 might be mid 60s, our cars mid 70s, etc.

I can't tell you that if you have headers and CSL airbox you should target 76% instead of 75% and if you are FI you should target 80.

Obviously chassis tuning is part of it, but if you have 800hp, you will run wider rubber and softer springs etc in rear.

[Obioban]

A large part of the reason I went with the GC front sway is that the bar is infinitely adjustable within its adjustment range. So, it fell in spec per the spreadsheet, and then I could dial it in to my taste specifically by changing the arm length.

[TosM3]

hmm interesting will read up

[r4dr]

Playing around with the targeted road speed table towards the bottom left, assuming all things stock in an E46 M3 coupe, can you conclude that BMW targeted 40 mph as the road speed for their factory flat ride? That would make sense given how cars are driven on the street, so if you wanted to skew towards high-speeds on the track you would target 80+? So perhaps a compromise dual-duty car would target 50-60?

[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)

After playing around with the spreadsheet a little more, I am trying to understand how people are choosing the Hz delta between the front and the rear. There is a section in the spreadsheet for "Flat ride calculator based on target road speed".

Obi, when I punch in your rear ride freq of 2.06 Hz, the flat ride calculates to a target road speed of 125 mph, to get 1.92 Hz in the front. Is there a reason you chose this? Is it for a flat ride at max speed on the track? I 'm having trouble determining what to target.

As a basis for comparison, 60 mph target road speed, with 2.06 Hz rear freq calculated --> 1.75 Hz front freq. Similarly, the stock suspension is set to 1.53 Hz rear / 1.27 Hz front for a target road speed of 40 mph.

[Obioban]

I was (am) working within the constraints of what my shocks can handle and what sways exist (to get the oversteer/understeer balance right without having no rear bar).

[duracellttu]

This past week I have been emailing TCK about spring options. I was wondering if he sold other spring rates, not listed on his site. Specifically for the rears.

I wanted to know if he could get 750# rear springs in the barrel shape. He told me that the SA damper wont support anything above 700# springs in the rear.

His recommendation was 400# fronts and 700# rears and that it had "great balance". This was after I told him I had a TMS front sway and OEM rear.

The flat ride calculator shows that to be a 2% flat ride (2.04Hz Front / 2.07Hz Rear) with 76.4% FRC. Sounds like that will have a bit of a harsh ride. Thougths?

[r4dr]

Be careful about tunneling in on one number and/or looking at that number in a vacuum. Every suspension setup is a compromise.

2% flat ride is still flat ride, it's not like either you have to be at *x*% flat ride at *y* speed otherwise the car will be bucking like a bronco. If you look at Shaikh's 330i entry on there, he runs 425/800 for 8% flat ride on what seems to be a dedicated track car (there are clips of it on his YT channel). I don't have personal experience with TCK Konis (only GC) but I've been told they're valved on the softer side as a philosophical decision versus GCs. He could also be limited to 700 in the back because of what dampers that kit runs.

All I'm trying to say is looking at 400/700 as a 2% flat ride and nothing else is kind of missing the rest of the picture. Just like how Obioban is adapting his "perfect world" flat ride numbers to the capabilities of his dampers. Personally I wonder how 350/700 would work but I have no idea if that will end up being too soft up front for the track.