Spring Rates - Track / Autocross

[CSG Mike]

Originally Posted by Dezoris

I hear you man, it totally blows. The only way it would be good is if you set up an event like you did for track days for autox.

I do know that the car understeers unless pitched to oversteer at low speed.... canyons...

[ayau]

Originally Posted by dwx

Before you even look at anything like spring rates, get a proper alignment... it could be way way off for all you know. Was your car aligned before with just the crash bolts?

I would look at disconnecting the rear swaybar if you really want to run rates that high.

I did get an alignment when I just had the crash bolts. The toes were zeroed out and I had about 1.2 of front camber. I'm guessing the current alignment shouldn't be way off since I'm only dropped about 1 inch.

I'll be scheduling an alignment soon.

[ayau]

One thing that Mike mentioned last night was when the oversteer occured. Was there oversteering during a static turn? I didn't really pay attention to that since autox courses generally don't have long sweepers. I'll try to pay more attention next time and see when the oversteer actually occurs.

Edit: I remember there were some short sweepers. If I remember correctly, I didn't have any major oversteer problems during those. It felt pretty neutral. The car broke during quick transitions. It was probably because of my jerky steering inputs, idk.

[Dave-ROR]

Originally Posted by ayau

One thing that Mike mentioned last night was when the oversteer occured. Was there oversteering during a static turn? I didn't really pay attention to that since autox courses generally don't have long sweepers. I'll try to pay more attention next time and see when the oversteer actually occurs.

Edit: I remember there were some short sweepers. If I remember correctly, I didn't have any major oversteer problems during those. It felt pretty neutral. The car broke during quick transitions. It was probably because of my jerky steering inputs, idk.

When it occurs is important. Alignment is key here also, it can drive straight but have lots of toe out, etc.

[Dezoris]

Pick up a camera and a suction mount. Post it up, much of it could be how you are driving. You have anyone close to you to go to an event that has any experience?
Get an alignment soon, camber changes will effect toe. You may have some wacky toe out in back which could cause the snapping oversteer you mentioned.

[Nick Dugdale]

We had some big names in this thread. Exactly 10 years later I come to revive it.

Second season racing the 2015 Subaru BRZ on Hoosier R7 and Maxxis RC1.

Current Setup:
2,650 lb MCW (Ratio: ~55F/45R). 9LR Wing.
MCS 2W-NR. 550F / 600R. Front 22mm WL ARB (soft setting) / Rear 16mm WL ARB

Notes from my 2022 NASA TT season:
• Notable understeer characteristics at all speeds.
• Steering feels precise and sharp.
• Confidence inspiring grip but need to resolve understeer state

Soon to test: (To combat understeer & maintain steering feedback)
• 450F / 550R with same bars
• 550F / 600R with softer front bar
• 450F / 600R with OEM 14mm rear bar

(I have a formula I use to calculate my components motion ratio's and it seems to work well for the setup.)

[Racecomp Engineering]

One thing that's changed in the last 10 years is that a LOT more people are running big wings. Street tires are also a lot better. Also I had more hair. But I did lose some weight!

Is your understeer on entry, exit, steady state? All of the above? How much camber?

- Andrew

[RedReplicant]

Also, what is your ride height front and rear? I'm at the opposite end as you are, the car has all the front grip in the world and not enough rear from time of on throttle through exit. I've got a few things to try on my side.

On your list there the last one is probably what I'd be trying, or 500/600 with stock 14mm. Obviously there is a power and weight difference between the two of our cars, but given we're 5 taking the same modifiers it should pretty much even out.

I am currently:
2871 MCW w/ 53/47 split
4" flat splitter, vents, Verus HE wing
400/600 Shaftworks 1way with 22mm Perrin on medium / stock 14mm
-4.5 / whatever stock rear camber ended up with at 22.5" front and rear bottom of 17" wheel to fender
17x9.5 255 RC1

I have a Mann Engineering rear bar on the car now, but I haven't tested it yet. Gut feeling tells me to go up a bit front rate wise but I am probably buying Xidas next week now that I know they're no points in 5.

[doward]

Another "TT5" car here, and it was absolutely peachy perfect at Mid O last month. Literally nothing I want to change. I'll be rolling it right into SCCA STX this weekend as it sits with just a fuel change and passenger/rear seat reinstallation.

949 Racing Xida 500/500lb
Whiteline 22mm front, full stiff
Mann Engineering rear, middle
no 'real' aero, taking NASA penalties for OEM STI/Limited trim lip/spoiler
-5.2 front, -2.8 rear, smidge of rake, smidge of rear toe-in.
Ride height is up a bit, but not measured recently, just to get it off the front bumpstops and retain the rake it had.
17x9 245/40/17 71RS/AO52

[lutfy]

Another ST/TT5 car here.

2770lbs

550lbs/600lb (f/r)
Stock OEM bar f and 2017 OEM rear
APR f splitter and GT250 flat pane rear wing.
-3.0 front, -2.2 rear, rake is almost even. Front all way down on MCS 2WNR shocks. Rear matched for corner balance.

17 by 9 ET45 with 225 R7.

Car is fairly neutral and the vehicle characteristic changed a lot since I installed the rear OSG LSD. Prior to that, I had 550/650 spring setup and it worked extremely well on the car.

Upon installing the LSD, the rear became handful until I reduced the rear rates. Played with shocks/heights, car was a handful.

This year installed the rear control arm and dialed out the rear camber to -2.6 and the difference was noticable. Car hooks up much better at exits (rear) but the front needs more bite now.

Will report back after getting the fronts sorted (wanted to tweak/test one axle at a time than both with new rules allowing for more camber adjustability).

[foshjowler]

STR car chiming in. I haven't touched any of the knobs since the car feels amazing as is. I bought the "package" from a friend after he sold the car and used the same setup since I knew it worked well. I should record the positions of the knobs in case anything gets messed up. I've considered trying out softer springs to try and improve the ride on the street since it's still my main car.



JRi 2-ways 450F/600R
Whiteline 22mm front bar, full stiff
Stock rear (I have a Perrin 16mm rear, but haven't found that the car needs it)
Alignment is -4* front and -2.2* rear. 0 toe in front and a little in on the rear
17x9 245/45-17 Yoks

[RT-BRZ]

I just moved my car to XA because I added Flex Fuel. I also added Shaftworks USA coilovers with 6K/9K Swift springs with Whiteline RLCAs (new model) and Whiteline rear toe links. I've only got to do a Test and Tune but the car feels a lot better now than when I ran Feals with 6K/7K springs.

We have an event coming this Sunday and I am doing HPDE and Time Trial this year so we'll see.

I also have front camber set to -4 and rear to -3 so that may be another part that's help a lot too.

[ZDan]

I still can't wrap my head around why anyone would want the same spring rates front/rear, or worse *stiffer fronts* given motion ratios of ~0.95 front and ~0.75 rear. About to install RCE Supersport-2 coilovers (7 kg/mm front and rear) on the new '23 BRZ and not at all enthusiastic about ~6.3 kg/mm front with 3.9 kg/mm rear spring rates, considering swapping in 5 kg/mm springs up front which would give ~4.5F/3.9R wheel rates.

Anyway, spent the last 5 years running '17 PP street/time-trials car, final/fastest setup:
~2900 lb. with fuel and driver, 53.5F/46.5R
4.4F/5.3R springs (Swift Spec-R), Bilstein B8
Just under 13" hub to fender lip front/rear (-1.5" vs. stock?)
Eibach sway bars, front soft, rear stiff (~150% or 2.5x stiffer than stock front and rear)
-3.5F/-2.8R camber, zero toe all around
245 RE71RS last year, 245 and/or 235 year before

This setup had highly annoying midcorner push, hoping to avoid that in the new '23 with RCE SS-2 coilovers...

[strat61caster]

I think the equal/softer rear main spring comes from a few ideas that some people seem to stick to real hard - zero toe, positive rake, bump stops that basically make the main spring useless, bound up or overly stiff swaybars, weird damping, ride heights. There’s too many variables to really nail down a “perfect” setup or say X/Y is the right combo, for better or worse I find this car to be really spring insensitive, especially if you’re dealing with a particular problem such as alignment issues or a compromise setup like a damper that’s inadequate or set wrong. For instance I’ve tried 325#/425#/500# in pretty much every combo, even 500F/325R, a degree of camber has had a bigger impact on balance then going +/-100# on the spring rate did.

Edit: also with a soft rear vs a stiff one I could see better driver confidence with a rear end that moves vs one that doesn’t move and you have to have a better feel for the tire slip angle as well as anticipate any track bumps/irregularities.