RCE SS-2 for '23, spring rates ?

[ZDan]

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...

[DocWalt]

Why so little front camber?

I do agree with changing up spring rates though.

[Lincoln Logs]

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.

[NoHaveMSG]

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.

[ZDan]

Originally Posted by DocWalt

Why so little front camber?

I do agree with changing up spring rates though.

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!

[ZDan]

Originally Posted by Lincoln Logs

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.

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).

[ZDan]

Originally Posted by NoHaveMSG

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.

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!

[Racecomp Engineering]

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

[ZDan]

Originally Posted by Racecomp Engineering

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...

[DocWalt]

Originally Posted by Racecomp Engineering

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

Agreed with going stiffer rear and not softer front

[jflogerzi]

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.

[ZDan]

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!

[Wangspeed]

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.

[ZDan]

Originally Posted by Wangspeed

Your valving, alignment, and tires will make a big difference too.

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.

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.

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.

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.

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.