GR86 - Understeer Alleviation - RCE Tarmac 2 (7k square setup)

[ZDan]

FWIW the few times I've installed coilovers, measuring to ensure same left/right free lengths (i.e. same amount of thread showing) while setting ride height, I've wound up within 1% of 50/50 corner-weights right off the bat.

If they have scales at the track perhaps you could check corner weights there and adjust if necessary.

[Tomyyyu]

Originally Posted by ZDan

FWIW the few times I've installed coilovers, measuring to ensure same left/right free lengths (i.e. same amount of thread showing) while setting ride height, I've wound up within 1% of 50/50 corner-weights right off the bat.

If they have scales at the track perhaps you could check corner weights there and adjust if necessary.

Yep. The 949 article mentions that too. But for sanity check and just to get #s too, I’ll just do both alignment and corner balance.

Now I’m working on trying to figure out my dampening settings. Which has been tough, before i even go race. On the street been following this process:

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So I started with everything at the softest position.

Start by driving around, feel out the car a little bit. Then come back to your garage/driveway to do a change.

1. Start by increasing front compression 2 clicks at a time, then go drive after each time you increase the damping. When the front start feeling harsh over bumps (skipping through bumps or jolting the chassis upward - trust me you will feel this), decrease it by 1 or 2 clicks.

2. Rear compression next, follow the same procedure.

3. Front rebound 3rd, increase this 1 click at a time until you feel like the front is oscillating in between 1 or 2 cycles. Then back off 1 click.

4. Lastly rear rebound. Follow the front rebound procedure but back off one additional click than front rebound (this is usually a rotation like rebound setting)

This usually come out to be running most amount of compression damping and least amount of rebound.

When you're on track/auto cross, drive the first session with your street set damping profile. If the car feels really wallowy and lazy, increase all 4 corners' compression by a few clicks (let's say 3 clicks). Then drive the next session with the increase.

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So I tried working on compression today, I ended up with -4 from full stiff (12 clicks total) for front and rear with 7/9k springs.

I must say I did find it hard to feel when the compression was too much, especially in the rear. It was notable the car would get more bouncy and even a little more sensitive over bumps. But it wasn’t as clear as I hoped to find that point where it got too harsh or skipping bumps. I think it’s close to where it should be though, just shocked to see it’s almost full stiff on front and rear for compression.

Tomorrow I’ll try rebound and see if that’s easier to feel out.


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[Tomyyyu]

Originally Posted by renfield90

Random grab bag of thoughts. Sorry it's not more organized, it's late and I'm supposed to be working.

My old T2 settings on 450lbs/in front and 550lbs/in rear:
Compression: 4 clicks from full hard (all 4)
Front rebound: 10 clicks from full hard
Rear rebound: 11 clicks from full hard

You want a stiffer rear spring on this car than on the front to make the suspension "flat." If you go too stiff in the rear, a 200tw tire (and/or your talent) will not be able to keep up. For me, too much was at 600lbs/in. Look into "motion ratio" and "natural frequency" if you want to dig into this more. A spring rate change is not the first change I'd recommend though.

If you are riding on the bump stops, your spring rate is not what you think it is. A bump stop acts as a spring in parallel which means the total spring rate is simple addition of both rates. And since a bump stop's spring rate is variable and very progressive...good luck! Get off the bump stops.

You do not have enough front camber and that is absolutely contributing to your understeer. If you can't get to -4.5 with your current plates, get new plates. This is IMO the first thing you should try, followed by getting the car off the bump stops, followed by a rear spring change.

From there I suggest finding a suspension adjustment flow chart and following it. Everyone has their own philosophy for how to tweak their car, but we're all mostly following the flow chart which provides a menu of options, and from there picking our own medicine (or in some cases, poison). Get your mid corner straightened out first because sometimes that will fix entry/exit as well.

Interesting. I’m on 7/9k so close to yours, mine is 400/500.

I did end up also increasing my ride height as I definitely was bottoming out the front on bumps. First thing I noticed on the street was much less rear weight shifting upon acceleration, that the rear seems to follow the front a lot closer, I actually get feeling from what’s happening in the rear, and the ride isn’t “crashing” anymore. Instead it’s stiff, but doesn’t crash. Will have to see how the 7/9k holds up in autocross.

For compression, from my own street test and tune and capabilities I ended up about the same, 4 clicks from full stiff for compression on all four corners.

I’ll be playing with rebound next using my steps (one of the posts on this thread).


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[cueball89]

Is that Devens? The talent pool out there is deep... Have someone take a run or two in your car, see if Evan is still out there. Drives a dark blue frs, crazy fast!

[Spuds]

Hope OP doesn't mind me piggy backing on this. I have the exact same issue with my '13 FRS and this has been helpful. Also another data point for the interested.

My current stx setup
T2s + camber plates, 7k f/r, Perrin 19mm front on stiff, stock (15mm?) rear, re71rs

Value: front/Rear
Hot pressures: 32/30
Caster: 7.5/-
Camber: 3.6(FL-limited)/2.3
Toe: 0/0
Bump: 11/7 from stiff
Rebound: 9/13 from stiff
Ride height: 335/340 wheel center to top of well

So in terms of things I have the time to try before the season ends, I can play with damper settings, ride height, and possibly sway bars. I could try eccentric bolts for more front camber but I would prefer not to use those.

Thinking of upping rake to about 10mm from 5mm. Possibly also getting a 16mm rear sway bar and working on damping from there?

[Tomyyyu]

Originally Posted by Spuds

Hope OP doesn't mind me piggy backing on this. I have the exact same issue with my '13 FRS and this has been helpful. Also another data point for the interested.

My current stx setup
T2s + camber plates, 7k f/r, Perrin 19mm front on stiff, stock (15mm?) rear, re71rs

Value: front/Rear
Hot pressures: 32/30
Caster: 7.5/-
Camber: 3.6(FL-limited)/2.3
Toe: 0/0
Bump: 11/7 from stiff
Rebound: 9/13 from stiff
Ride height: 343/348 wheel center to top of well

So in terms of things I have the time to try before the season ends, I can play with damper settings, ride height, and possibly sway bars. I could try eccentric bolts for more front camber but I would prefer not to use those.

Thinking of upping rake to about 10mm from 5mm. Possibly also getting a 16mm rear sway bar and working on damping from there?

What does FL Limited mean?

But yeah, this is pretty easy off the bat. 7k square doesn’t work. Especially with the bar you have. You could either try the OEM front bar or try 9k rear springs due to the motion ratio of 0.95 front and 0.78 rear for the second generation (which is similar in the 1st gen).

The more rake you have the less rear grip, and vice versa. We would need your pinch weld heights to give you a better reference.


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[Spuds]

Originally Posted by Tomyyyu

What does FL Limited mean?

But yeah, this is pretty easy off the bat. 7k square doesn’t work. Especially with the bar you have. You could either try the OEM front bar or try 9k rear springs due to the motion ratio of 0.95 front and 0.78 rear for the second generation (which is similar in the 1st gen).

The more rake you have the less rear grip, and vice versa. We would need your pinch weld heights to give you a better reference.


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Front left is hard over on both the camber plate and lower strut mount slot. Can't get more than -3.6° at current height. Might lower the front to get a wee bit more.

Floor to pinch welds jack points is ~130/136mm.

I'm not sure allowing more overall roll is the answer though because that's how you lose camber?

[Breezio]

Originally Posted by Spuds

Front left is hard over on both the camber plate and lower strut mount slot. Can't get more than -3.6° at current height. Might lower the front to get a wee bit more.

Floor to pinch welds jack points is ~130/136mm.

I'm not sure allowing more overall roll is the answer though because that's how you lose camber?

Saying '7k square doesn't work' isn't accurate....

In any case. Too me it looks like you need more front camber, then a bit more rake and either more rear bar, or less front bar. Not talking swapping to oem FSB, but perhaps moving to the soft setting. I think that ideally you'd stiffing up the rear some instead of softening the front. But without changing hardware, your only option is rear dampening settings and/or front sway bar setting.

What camber plates are you running? I'm surprised you can't get more. I'm on T2's and Vorshlag plates. No special hardware in the strut to knuckle connection, just pushed in as much as the slots will allow then camber plates at max. Sitting at -4.3 camber.

[Spuds]

Originally Posted by Breezio

Saying '7k square doesn't work' isn't accurate....

In any case. Too me it looks like you need more front camber, then a bit more rake and either more rear bar, or less front bar. Not talking swapping to oem FSB, but perhaps moving to the soft setting. I think that ideally you'd stiffing up the rear some instead of softening the front. But without changing hardware, your only option is rear dampening settings and/or front sway bar setting.

What camber plates are you running? I'm surprised you can't get more. I'm on T2's and Vorshlag plates. No special hardware in the strut to knuckle connection, just pushed in as much as the slots will allow then camber plates at max. Sitting at -4.3 camber.

Vorshlag plates. Idk it's really weird that I can only get -3.6°, the other side would probably max out at just under -4°, but I want to keep it consistent side to side. I could probably get more static camber going lower up front but then I might start running into other geometry/travel issues.

I think I'll get at 16mm rear bar, those are somewhat easy to swap out.

Was looking at rake earlier today. If I could swing some more drop up front that would help with both rake and camber...

[Tomyyyu]

Originally Posted by Spuds

Vorshlag plates. Idk it's really weird that I can only get -3.6°, the other side would probably max out at just under -4°, but I want to keep it consistent side to side. I could probably get more static camber going lower up front but then I might start running into other geometry/travel issues.

I think I'll get at 16mm rear bar, those are somewhat easy to swap out.

Was looking at rake earlier today. If I could swing some more drop up front that would help with both rake and camber...

I would avoid the rear bar. 949 is pretty adamant on that and he’s a knowledgeable poster.

https://www.949racing.com/supermiata...lignment-info/


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[ZDan]

Originally Posted by Tomyyyu

I did end up also increasing my ride height as I definitely was bottoming out the front on bumps.

If you've been bottoming out the front, IMO that is most of your understeer problem. I'm guessing the Tarmac 2s might have less front bump travel than RCE SS-2 I'm running. I'm at 330F/335R ride heights. Was amazed at how much less mid-corner understeer vs. my old '17, which had less front bump travel...

[Breezio]

Originally Posted by Spuds

Vorshlag plates. Idk it's really weird that I can only get -3.6°, the other side would probably max out at just under -4°, but I want to keep it consistent side to side. I could probably get more static camber going lower up front but then I might start running into other geometry/travel issues.

Interesting. If you haven't already, loosen up all the bolts and shove everything in. Taking up as much as tolerances will let you. Might be able to squeeze out a little more camber. You really should be able to get more camber then your getting.

[Spuds]

Originally Posted by Breezio

Interesting. If you haven't already, loosen up all the bolts and shove everything in. Taking up as much as tolerances will let you. Might be able to squeeze out a little more camber. You really should be able to get more camber then your getting.

Yeah, the plates are pushed all the way inboard, even started looking around for warping/damage but couldn't find any reason outside of manufacturing tolerances.

[Spuds]

Originally Posted by Tomyyyu

I would avoid the rear bar. 949 is pretty adamant on that and he’s a knowledgeable poster.

https://www.949racing.com/supermiata...lignment-info/


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That article also says "For track use, slightly bigger bars are a good overall compromise". Moving from a 15mm to a 16mm adjustable bar isn't likely to kill the handling.

It also says to stay above 140mm ride height... Maybe I went lower than I thought I did...