Hindsight2010

Went from stock setup to some Ohlins coilovers, lowered a tiny bit (maybe 10mm, keeping rake the same), corner balanced (though it came up perfect 50.0 crossweight when I turned the scales on!), added rear bump-steer adjustable toe-links, and changed the alignment settings. Now the car feels very unstable when braking hard from high speeds - it seems to hunt and feel floaty.

Not sure what alignment settings were prior to this but would assume they were stock since that is how I bought the car. Didn't have any issue with braking stability before.

My alignment is now:
-2.2 camber front, -1.8 camber rear
8.8 degrees front caster
Front TOTAL toe is negative 0.12 degrees (AKA 7 minutes) or about 1.5mm total (as measured from tire surface, not wheel lip)
Rear TOTAL toe is 0.47 degrees (AKA 28 minutes) or about 6mm total (as measured from tire surface, not wheel lip)

I would like to know if the alignment looks good to you (I would run the same as above for the track except maybe go to 0 toe in the front and up the front camber to -2.8 and rear to -2.2). If the alignment settings look good, I'll need to check the bump-steer adjustable rear toe-links. I only eye-balled them to figure out the shim stack height. I have a bump steer gauge but it takes forever to check, set, recheck it so I was hoping I could get away with just eyeballing it for now. Maybe that's not the case and I introduced some rear bump steer with these mods. Aside from alignment, that's the only thing that could explain it.

Thanks in advance

Spyerx

How’s your diff ?

you didn’t mess with the compression links did you? Change roll centers?

Hindsight2010

Sorry, I should qualify the car is not a GT - it's a .2 C2S, but for the purposes of my question, it shouldn't matter. I'm posting in here because this is where the most alignment and setup experts congregate. I believe the LSD was an option on the non GT cars but I don't have it.

RE compression links, I removed them to change out the LCAs but otherwise no. They are original OEM and in good shape.

Auto_Werks 3.6

Those alignment numbers don't look crazy. I bet the car had 0 front toe when it was setup stock. I would try 0 front toe and actually check the settings on your bump steer parts you added.

Hindsight2010

Will do thanks. I have a string alignment setup and camber jig so I can do all that myself. Just a pain to get the car shimmed up to level on all 4 tires. I read a lot of guys go with 0 front toe.... I just figured the car wouldn't track very straight like that so I added the smallest amount I could reliably measure. I will put it to 0 though and see what happens, and bite the bullet on the rear bump steer. Ugh really not looking forward to that but it needs to be done.

Spyerx

if you didn't mess with the squat / roll center etc.
And you only get this under threshold braking
Diff, high probability, if you have an open diff, you'll feel that back end wobble
Ensure your rake is spot on, should be a bit ***-up
Check rear toe again
And up front run it 0 or slight in. toe out gives sharper turn in but mid corner load you get less steering... i like a tick of toe in up front

Hindsight2010

Thanks for the reply. I didn't mess with squat or roll center that I am aware of, however, I did NOT measure the car height prior to making suspension changes. What I did do was check the factory service manual to obtain the ride height for my year C2S, front and rear, noted where you are supposed to measure from front and rear per the manual, and then used a laser beam to set the front and rear ride height to some amount lower than stock, but evenly front and rear. I got it within 1mm per wheel, and when I corner balanced it after, the cross-weight was 50.0 right off the bat (so nice not to have to adjust). I'm at 110mm front and 130mm rear ride height. C2S has different rake than the GT cars and I think that's due to GT cars having the rear wing. Anyway, squat should be same as OEM on my car.... just lower now.

Now that I put more miles on it, I can give additional detail on your threshold braking. I notice that the car feels unstable under high-speed threshold braking, AND now when I lift off the gas in a corner, it feels very unstable too for a moment as the rear becomes unloaded. This is really making me suspect rear bump-steer issues, and reinforcing that I need to get my bump steer gauge on the rear and set it properly. What do you think? As for the open diff, I don't remember any instability when lifting mid-corner before so I'm not sure it's that.

I will double check front and rear toe again per your recommendation!

Thanks again!