RCE SS-2 for '23, spring rates ?
 

I'm about to install RCE Superstreet-2 coilovers on my '23 BRZ. Spring rates are 7kg/mm all around. I'm thinking about getting softer springs for the front to keep wheel rates more in line with front/rear weight distribution and to mitigate the inherent understeer this car seems to have (my '17 did anyway, on 4.4 kg/mm front and 5.3 kg/mm rear springs).

The car will be my daily-driver, but I'll also compete in time-trials with it with COMSCC. Competition is stiff at the sharp end of my class, so willing to compromise streetability for tenths of a second!

Tires will be either 225 A052s or RT660s.
Target alignment specs -3.5 front, -2.5 rear camber, zero toe all around.
Ride heights -30mm front, -25mm rear
Competition weight 3050-3100 lb.
No aero

Thinking I'll go 5kg/mm front with 7kg/mm rear. But maybe 7F/9R...

I may just try the 7 all around they come with as a baseline but honestly it just seems like it will be an inherently understeery setup, with wheel rates of ~6.3 front and ~3.9 rear, YUK...

Anyway, expert opinions welcomed! TIA...

Why so little front camber?

I do agree with changing up spring rates though.

Base line them but make sure you have your ride height with .25" of rake with the rear being higher. It makes a significant difference in balance. After that make changes as you see fit.

Will a pair of 10k's work? I have a full set of 6k, and 9k, but I planned on selling those with my T2's.

Honestly I haven't noticed that much difference between -3.0, -3.5, up to -4.0 up front. Seems like a pretty broad range that will work. RCE says people run up to -3.5, I think the design of the top of the strut and camber plate limit how much you can get.

I'm not worried at -3.5 or -3.25 even, but it better be more than -3!

Yeah the plan is something like -32mm front, -25mm rear and go from there.

The '17 was about -35 all around, I'm thinking that's where some of my understeer was coming from (super-low rear roll center).

Hmmm...
It is my street car so keeping it a bit on the soft side is preferable. I've historically done pretty well with softer-sprung track cars anyway. Ability to curb-jump comes in particularly handy at Palmer CW!

Try it first!

Would probably not go softer in front for you, maybe stiffer in rear. Your old car with relatively soft rates was likely still using the bumpstops quite a bit in cornering even if they were trimmed.

- andrew

Troof! Honestly though I kept the factory rear upper mounts and full-size bump stops to make sure rear was more "bump-stop-active" than the front. Up front I cut the Bilstein bumpstops in half. Going over a sizable bump, it would definitely ricochet more off the rear bump stops than the fronts.

But yeah, still could well be a factor in my '17s understeer...

Agreed with going stiffer rear and not softer front

Listen to RCE. 7K is pretty decent. Are these for a new GR/BRZ? If so remember the new chassis is stiffer so you can afford to be a bit softer on springs.

9kg/mm springs for the rear on the way, thanks @NoHaveMSG !

Running the numbers, I get 2.1 Hz both front and rear running 7kg/mm front springs and 9kg/mm rear.

We'll see how it goes in a couple of weeks at Palmer!

Your valving, alignment, and tires will make a big difference too. I don't have Racecomp coilovers, but I dropped my rear spring rates on my MCS setup to 400 lb/in front and rear (7kg/mm), and the car is much better suited for street and track usage. 400F/500R was decidedly not fun over big expansion joints while in a turn, nor as the weather got cold.


I suspect a lot of folks that understeer on 400/400 with lesser coilovers are likely riding front bump stops, sending rates sky high. Don't lower the car too much.

Yeah, expect all of those would have a more profound effect on handling and handling balance than the difference between 7kg all around vs. 7kg front with 9kg rear springs.

Surprising, I would not expect a huge difference really. FWIW when I went from 11/11 spring rates on the FD to 11/13 (Ohlins) I noted barely any difference in handling balance.

Then again 400/400 spring rate biases stiffness to the front.

Honestly I don't think it's going to make any profound difference in handling balance. I'm just trying to mitigate understeer, I still expect to get some. I will be *very* surprised if 7F/9R results in an oversteery car but we shall see.

Will go over this with RCE, but plan to lower the car something like 32F/25R. RCE SS-2 include rear top mounts which I *think* increase bump travel so less worried about bottoming the rears too soon which could result in unexpected oversteer.

Ex COMSCC member, say hi to Marc Epstein from me.

Having tried multiple spring rates, rake, alignment etc here are my .02 cents.

I would not go below 400lbs in the front. Under braking, there is a fair amount of dive. If you could run 450lbs front and rears, that would be somewhat ideal for street/track.

I went with 550/550 with full aero and the car pushed a fair bit on high speed sweepers. Went 650 rear and it was too much. 600 worked out fine.

The 50lbs delta was due to a large wing at the back (and front splitter). Square setup worked very well for me without aero.

The gentleman who posted .25 high rear rake is correct. Mine is almost even after corner balance but that was the starting point. Anything more, the car would skate under braking (my observation) and I couldnt get the desired rear camber.

For years I ran -3 f and -2.2 r negative camber. It was not enough and I would tear up the Hoosier R7 but was limited to class rules.

Now that I am running -3.8 f and -2.8 r, during testing day, I was able to drive with the steering and throttle and its a different car all together.

Testing with Goodyear SC3R they liked -3.5/-2.5 and anything less than that, I was eating up the outside (f/r). The only way to get the f camber is through camber plate maxed out and camber bolts at the bottom (in your case).

Also smidge toe in at the back helps a lot at high speed sweepers. I tried 0 toe and the car was a touch sketchy on fast downhill corners. I suspect there is some toe change during rear wheel travel.

Good luck!

Dynamic toe is pretty linear and negligible in the typical working range of the suspension, you have to completely unload the rear to get measurable toe change. That’s not to say you weren’t feeling something, there’s a lot of variables but I agree there’s no real reason to run zero rear toe unless you’re band aiding a pushy setup.

OK, will do! Will he know you as "lufty"?

Yeah, I did pretty alright for years on more street-oriented springs/dampers (4.4F/5.3R with Bilstein B8s), slaying the competition in my class, but now a hotshoe is driving one of the NCs I usedta kill and took my class last year (I got 'im in mixed conditions at NHMS last month though)! I don't wanna leave anything on the table, so bumping up the suspension to be a bit more track-oriented.

Huh, I would expect aero changes to be a lot more effective at addressing high-speed balance than modest changes to rear spring rate?

Could still try 7kg/mm "square" spring rates, but always important to note that that is very UNsquare as far as wheel rates. 90% going to go 7F/9R right off the bat based on experience with the '17.

Cool, definitely will be running at least 0.25" rake.

Plan to run max negative camber via the oval upper holes where strut mounts to upright/hub assembly, and adjust up top to -3.5 front which worked great with the 17, should be even better with stiffer suspenders.

Was gonna go zero rear toe but will amend that to 0.1 degrees total rear toe-in. And zero up front.

Thanks, I'm really looking forward to Palmer June 3! Holy crap that's coming right up...

Yeah he knows me by Lutfy :)

The rear spring delta was more on slower speeds, the 100lbs delta was too much and I couldnt power out as effectively/agressively. Square setup with the rear wing and I could feel push over 40-50mph hence the 50lb delta I know I have. But this is based on my personal experience.

Cheers,

Lutfy

Update: Finally got to track the car at NJMP Lightning last Mon/Tue with COMSCC! Overall had a great time! The car was very well balanced, definitely less understeer than previous setup on the '17 :) Still got some understeer carrying speed from 2 into 3, very easily could tighten the line to make T3 apex with little taps on the brakes. Could either throw it into Turn 9 (extended banked right-hander) and get it to rotate a bit and scrub speed, or brake a bit more and carve around T9, either could crank steering in to make late apex without undue understeer. Nice! Definitely glad I went with the 9kg/mm rear springs, THANKS @NoHaveMSG ! Seems to work quite well with my car. Won T50 class by 1.4s! Sweeet...

Time-trial setup:
3120 lb. (3107 lb. minimum for class) with '17 spare tire + 100 lb. ballast in spare tire, full tank, 53.5%F/46.5%R
RCE SS-2 coilovers, 7kg/mm front 9kg/mm rear springs, 12 clicks-out front, 10 clicks-out rear
330mm hub to fender all around (-35mm front, -30mm rear)
-3.15F/-2.5R camber, 0 front and 0.1* total rear toe-in
245/40-17 RE71RS on 17x9 +42 wheels (borrowed from Doug F., THANKS!)

Ran 1:16.29 time trial despite screwups each lap. FWIW Doug's 245/40-17 RE71RS with +40 lb. more ballast were nearly 1s faster than my 225/45-17 RT660 :O

https://www.comscc.org/events-result...s/#third-event

:burnrubber:

- Andrew