This year I've been to TGPR in February, Putnam in April, and TGPR again in May.

At TGPR in Feb the specs/conditions were:

AMB Temp: 70 deg (warm for Feb)
Cam F: -1.7
Cam R: -1.5
Caster: 7.0
Toe F: 0
Toe R: .09 in
2nd event on 255/45-17 Direzza ZII

At Putnam Park in April the specs/conditions were:

AMB Temp: 55 deg
Cam F: -1.7
Cam R: -1.5
Caster: 7.0
Toe F: 0
Toe R: .09in
3rd event on 255/45-17 Direzza ZII

At TGPR in May the specs/conditions were:

AMB Temp: 85 deg
Cam F: -2.0
Cam R: -1.7
Caster: 8.0
Toe F: 0
Toe R: .13L/.17R
4th event on 255/45-17 Direzza ZII

For the 1st TGPR and Putnam I ran with the same alignment specs. The car felt pretty solid, very neutral, leaning towards understeer at the limit. Before the last TGPR, I added some camber to try to help with understeer a bit and just overall improve cornering. I've heard from a few people to max caster before setting camber, and we settled at about 8.0 deg with my desired camber.

So, at TGPR, overall I was about 1 sec slower than I was at my previous outing, and the car felt "looser" overall, and less "hunkered down" while braking. My times were much less consistent overall. I can't say that the handling felt "bad", but I did not seem to have the stability the car had at the previous two events. It did push more toward oversteer at the limit, but only under full throttle in a turn. I will say that the temps were much higher than my previous event at TGPR, but not what I would consider scorching (though I did have some cooling issues later on in the day).

Based on the info above and any more you'd like me to provide. What could be the cause of the instability. I was under the impression that -2.0 was not ultra aggressive for track use. Am I wrong?

I've been running 38psi F/36psi R for the last few events, though my fastest lap of this last session was one of my 1st laps of the 1st session while they were still a little cold!

Were amb/ temps a factor?

One flag marshall said it had been raining recently, would "green" track conditions cause instability symptoms?

Should I dial back down my camber/caster or look for other variables?

Could diff camber setting require diff air pressure?

Looks like a pyrometer may be in my future.

 

Street tires, get used to it ....

 

I agree with TeamRX8. Are the tire pressures you stated your cold starting pressures? If so I think they're too high. Those sound more like good HOT tire pressures.

 

I was only half joking. Street tire grip will vary a lot due to surface and condition changes. You went from 0.09 total rear toe to 0.30?

 

My 2 cents: reduce rear toe-in a bit. Your caster seems high (for my taste).

+1 on tire pressures.

 

prev Rear Toe: .09 L/.09 R in degrees
what does .09/.09 and .13/.17 translate to in inches? 1/8th, more?

Tire pressures are hot pressures right off the track.

What negatives could I be seeing from high castor?

I've been to four track days (the above three and Road Atlanta), so I'm new to feeling feedback from the car and adjusting, as well as what settings are too much or too little. This is also my 1st set of "good" street tires, and they only see HPDE use and the road trip there. So really, i've only seen their traction on different tracks with no real comparisons, until now.

Thanks guys for all your input. So could I chalk this up to track conditions? If I have too much rear toe in, what symptoms are showing from it? The instability?

Keep camber where its at?

 

Assuming 25.1" tire diameter, 0.18 deg total = 0.079" total toe

0.30 deg total toe = 0.131" total

Pretty simple though. Go back to previous alignment and re-evaluate.

I run min caster; 4 deg or less

 

I'm would be surprised that you would notice the difference from 1.7 to 2.0 camber in the front...and the rear camber isn't much different either

I would look at tire pressures and temps to try and fine tune things a bit

The warmer air will slow you down a bit...and a sec on a couple minute lap isn't much

The rear toe in should make the rear more stable rather than less...but if they are warming up more you will notice that in more tendancy to oversteer

You also might just have been overdriving certain areas of the corner as well....often I need to slow down my entry after a couple of track days...to end up going faster overall.....