I decided to build a tool to make more arguments. Click around and have fun.

Trying it out now, its really cool, and I need to learn about FLLTD. I have used an excel that's similar in function for years, mainly to give me a front roll stiffness % to target setups around.
Data points for me:

GT500
When my car had more rear aero bias 57% was a good balance.
Now with more front downforce (6" splitter) and stickier tires (Bridgestone) I am up to 60%

GT350
On BMR springs and bars, with square 315/30/19 RT660's, and no aero went fast with 54.5%

FLLTD is Front Lateral Load Transfer Distribution. It takes sprung and unsprung load transfer into account. These are all static values, but it gives us a way to describe all these combinations in a quantitative way to describe a combo as opposed to in the touchy-feely way we've been doing it forever. You can put your individual car's corner weights in if you wish. The unsprung masses are estimated. Those need to be actually measured.

Super nice, and I imagine it will be a big help for S550 folks. Do IRS folks run no rear sway bar, or is that just us stick axle Neanderthals? You know what I'm going to ask for - can you make an S197 version?

Dave_W said:

Super nice, and I imagine it will be a big help for S550 folks. Do IRS folks run no rear sway bar, or is that just us stick axle Neanderthals? You know what I'm going to ask for - can you make an S197 version?

Click to expand...

I've run without it, but I prefer having a small bar hooked up. Running disconnected is great for rear grip, but you lose a lot of transitional response.

If you give me all the numbers, I'll make the calculator.

So I’m sorry to be slow, but is FLLTD the percentage of lateral weight transfer in a steady state corner that is being carried by the front tires versus the rear?

Awesome tool and calculator, very cool.

This is brilliant...

Dave_W said:

Super nice, and I imagine it will be a big help for S550 folks. Do IRS folks run no rear sway bar, or is that just us stick axle Neanderthals? You know what I'm going to ask for - can you make an S197 version?

Click to expand...

TeeLew said:

I've run without it, but I prefer having a small bar hooked up. Running disconnected is great for rear grip, but you lose a lot of transitional response.

If you give me all the numbers, I'll make the calculator.

Click to expand...

Been working on getting my baseline and have tried so many combinations but feel I'm getting closer to something great. But one of the tests I did this year was with and without rear bar on the same day. I'm boosted so getting power down is pretty critical. With the torsen its super sensitive to unloaded inner wheel and once it breaks loose the inside it really lets loose.

Basic setup, 550/700 coilover, eibach FSB, and 20.0 and 22.2 oem RSBs. 315 re71rz square. Billet uprights also effect things here with the reduced roll couple, but still A/B testing should be relevant.

I ran an event with the 22.2 rsb and steeda 35mm front and soft or med didnt matter, the rear was useless. It just wanted to do rolling burnouts.

Next event I swapped to eibach FSB where full stiff is same as steeda full soft. I ran morning at full stiff with 20.0 bar. Car was good, put power down no problem out of corners, lift rotation was feeling decent though could use a bit more. Afternoon I pulled the rear bar and set front to medium. The car felt a bit numb and pushy but would have been interesting to test with 50lb more rear spring.

I put it back to FSB on stiff and 20.0 bar and did a little shock tweaking and it was feeling pretty amazing. Absolutely best I've been so far. Far better than we were at Packwood Tour and Pro. Comparing to our local fast guys, we had a solid second over Tour times and 0.5s over Pro times. Tour/Pro was no rear bar and shocks were WAY TOO STIFF.

So yeah, long story short. I absolutely recommend the 20.0mm base model bar.

Dallas J said:

Been working on getting my baseline and have tried so many combinations but feel I'm getting closer to something great. But one of the tests I did this year was with and without rear bar on the same day. I'm boosted so getting power down is pretty critical. With the torsen its super sensitive to unloaded inner wheel and once it breaks loose the inside it really lets loose.

Basic setup, 550/700 coilover

So yeah, long story short. I absolutely recommend the 20.0mm base model bar.

Click to expand...

This is my biggest complaint about the Torsen. There's no preload, so braking is always compromised and any time the inside rear is unloaded, you have an open. Even the Traction-Lok is better in this regard. The OS Giken would be the one you actually want.

Is this spring combo on an S550?

That's the rear anti-roll bar I've settled on as well.

I am going to spend way too much time nerding out over this. Thank you for making it

TeeLew said:

This is my biggest complaint about the Torsen. There's no preload, so braking is always compromised and any time the inside rear is unloaded, you have an open. Even the Traction-Lok is better in this regard. The OS Giken would be the one you actually want.

Is this spring combo on an S550?

That's the rear anti-roll bar I've settled on as well.

Click to expand...

Yeah, this is my 2020. 550 front is still pretty soft so next year I'll switch to 700/900. And thats coilover, multiply by 2.44 to convert to equivalent divorced.

700#/in coil-over is plenty stiff. I can't see any reason why you'd increase it, regardless of what you end up running on the front.

The natural freqency isnt too bad, but even a stock GT4 rs is stiffer. We're about 2.4x/2.3xhz and the spring change bumps that to 2.7x/2.6x. Cant find the limit till you exceed it

For reference, my Evo runs 3hz front and 4hz rear (the rear is cause when it matters, you're on 3 wheels).

Stiffer =/= faster

But it doesnt not = faster either. I do A LOT of testing so always working on whatever is next. I create a baseline, then come up with a plan to deviate and decide if that new setup replaces the old baseline or if I go back.

The relative stiffness though, 700/900 isnt anything crazy. SuperStreet (autocross) is as stiff from the factory. 3.0/4.0 hz in the Evo was 800/1450, I tried dropping to 700/1300 and it was compliant but not as responsive and slower overall. Internationally there are teams running 1000+ front rates.

I dont want to highjack your spreadsheet post though, I always appreciate a good spreadsheet! I have many and will steal this to add to them

We can talk off line if you wish, but my opinion is we do not have anything remotely close to the type of tire it takes to run any of those rates.

This is pretty interesting. Is there anything other than the drop downs that make this S550 specific?

The metric/imperial buttons only seem to change the anti-roll bar input units and all of the output units. Is it possible to change vehicle assumptions/geometry to also change with those buttons? I know could introduce more room for error/bug

RinerAuto said:

This is pretty interesting. Is there anything other than the drop downs that make this S550 specific?

The metric/imperial buttons only seem to change the anti-roll bar input units and all of the output units. Is it possible to change vehicle assumptions/geometry to also change with those buttons? I know could introduce more room for error/bug

Click to expand...

It's written to be as S550 specific as I can make it. I've made all sorts of assumptions, so it won't be perfect. There are no actual suspension geometries involved. Most good racing springs are #/in (at least in the US), so I left them in imperial units.


^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Click on this. I think it will be what you're looking for if you want to tailor the numbers to your car. A live rear car is going to be a little different in how it produces ride/roll rates, but you can tune it for the S550/650 variants.

TeeLew said:

A live rear car is going to be a little different in how it produces ride/roll rates, but you can tune it for the S550/650 variants.

Click to expand...

For the front McStruts, the motion ratios are probably close if not the same for S197 and S550. But I'm guessing the rear motion ratios are quite different for the S197 stock / divorced live axle setup and the S550/650 divorced setup. For "coilover" setup they should be closer, if not the same (haven't compared actual shock attachment points). For S197 using "divorced" springs, the calculations for rear roll stiffness will be different. Ideally, an S197 version would include rear roll center height adjustment which I think would affect roll gradient, and maybe even rear control/trailing arm angles to calculate anti-squat.

Mac Struts are always somewere about 0.95, so ya, 197, 550 or 650 is all the basic same. The rear is chalk/cheese.

For a live, and I haven't played with many, the distance between your springs, or spring base, becomes very important. As the base widens, the roll motion ratio goes up. As it narrows, it goes down. If it's really narrow, you have basically no roll-resistance due to springs. It's bar or nothing. The ride motion ratio will have stayed the same no matter the base measurement.

Live rears can get very, very complex. You not only have the normal anti's to play with, but you also get the torque reaction to try to manage. Roll steer is a big tool to use to make the car work. Camber is a big deal, but it's not something you can't change much once it's set. Roll center type and placement matter, as well as how it migrates. For something that has been around for so long, there are a lot of ways to get it wrong.