Rear toe suggestions
 

Guys, I read some threads here, but I'm not sure what to do...
I have -1.5 degrees camber and 0 toe front and rear.
When I step on the gas with turned wheels the back seems to spin fastly...
Do you think that giving 0.1 degrees rear toe in per wheel will help?
Thank you very much!

My preferable settings for road are the camber settings you already have,
1mm per wheel to out front (for better steering response),
1/2mm per wheel toe in rear (for better rear stability).
Some more camber for track use, depending on the tires and the specific track.
1mm for 18" wheels is about 8' toe per wheel.

0.15° toe in total can help stabilize the rear.

Mark Higgins BRZ in the Isle of Man uses more or less the same alignment for the special stages that are on public roads, similar with most other European roads (2:16"):
https://youtu.be/wEUhyOxQlf8?t=136
Bear in mind his car is a road car with road bushes and except his coilovers and roll bar it's completely similar with ours!

Are you referring to wheel spin? If so, I don't think alignment will make a big difference unless you currently running an extreme amount of camber or toe. I would suggest playing with tire pressures and getting better tires or LSD.

As reference, I'm running 0.18° total toe-in for the rear and I also encounter wheel spin issues which I attribute to low-grip situations and poor LSD. How you control the throttle and the vehicle speed will also affect how severe the wheel spin is.

Although I prefer the car to be as stable as possible cause it makes you drive it faster I'd like the rear sliding whenever possible, with the above settings sliding is simply more controllable

Can you give us an example of when it doesn't seem appropriate that you'd lose rear grip and you do?

For example-

The behavior you're experiencing should be expected if:

You're already turning and press the gas pedal hard suddenly
You're driving on a road with debris ( sand/dirt)
You're driving on a tire not meant for performance driving
You're at a high RPM when you start applying gas pedal pressure
You're facing downhill and turning
Your tire pressures are too high
Your new coilovers have too much rebound
Your new coilovers are bottoming out mid corner

Regarding the behaviour, my car was always like that, but I always had 0 toe. I pointed to the old suspension setup, but this is not the case.
225/40-18 Pilot Sport 4 (not S, not available in EU).
The issue is (I don't know the correct english terms): the only way to prevent spinning, is giving (a few) retarded gas just when I'm going out of the turn, if I anticipate the back starts spinning.
Tyre pressure is 2.4 bar on all 4 wheels, with a professionally calibrated manometer.
This happens a lot on slow turns (2nd-3rd gear), and not at high speed.

How old are the tires? My personal experience with Michelin is that they do not age well and grip drops off even though you might still have tread left.

Maybe consider dropping the rear tire pressure to 2.2 bar? I hear of people running 2 bar for autocross when using extreme summer tires such as Hankook RS-4 or Bridgestone RE71-R. I've never driven on the Pilot Sport 4 but I assume it also has a decently stiff sidewall.

Toe-in won't prevent wheels from spinning out if you give engine too many beans or car lacks grip (due tire choice, aero setup, road pavement type, overload or mass transfer at specific maneuver).
However car will still feel more stable even if traction loss. Even on ice/snow car you will need to fight/correct less to keep going straight with rear wheels drifting, i found also being able to accelerate out of corners easier, step on gas quicker, with rear toe-in, vs zero toe, which imho was too nervous, and while eases rotation, i prefer minding other things on track then spending all concentration workarounding or getting ready for alignment quirks.
Toe-in is like presteered wheels to centerline of car. When car gets slightly sideways, one wheel doesn't push inside anymore, while wheel on side car's rear slipped to steers in even more, tending to restore car to straight trajectory. When in corner you lean less on inside tire, more on outer, due mass transfer more grip going to outer tire that is pre-steered inside again trying to move that car end with toe-in back inside turn, not slip out.
Drawbacks are slightly increased tire wear (but not that bad to make tragedy of it, if toe is within reasonable range), and a bit less willingless to rotate that end in turns, but as everyhing is compromise, i much prefer that extra stability, from what i tried in different alignments, as there are several means to get more rotation with driver inputs, if wished.
If you decide against rear toe-in .. at very least set toe on both sides as even as possible.

1) Stepping on the gas with the wheels turned is generally thought of as bad technique. The fix is in your steering inputs.

2) Most people seem to prefer some rear toe in for stability.

steverife: obviously i do (1.) simultaneously & proportional to unwinding steering wheel back, opposite to trail-braking. Still, zero toe was a bit too nervous, too often did mistakes with accelerating out (and obviously having to lift or countersteer noticeably hurt exit speed), due what erred on safe side way too much. Rear toe-in helped a lot.

Happened to me with MPSS on the FD. I thought something was "off" with my setup as well for a while, but in the end the tires had just gone from quite good to utter garbage over the 8 months or so I had stored them while driving on NT01s throughout track season. Also had about half tread depth remaining. Tires were 2 years old.

It's not a tyre matter, it has been always so with 3 different new tyres. I think that @churchx focused the exact behavior.

Well, it ain't rear toe either... I've had "more rear toe = more stable" preached to me but for me it has never done anything but make great-handling cars either criminally unresponsive at turn-in, or even make them behave more nonlinearly and diabolically (AP1) even in a straight line. Dialing in rear toe-in is not going to fix what you are describing, which to me still sounds like a combination of the 55/45 F/R weight distribution we are stuck with and tires that aren't particularly grippy.

I'd stick to zero to 0.1 degrees total rear toe-in. Adding rear toe-in isn't going to magic you more grip, but it will make the car less responsive and less fun to drive.

It's not a matter of more grip, it's that when it loose grip it's sudden and not progressive. For sure it's not the PS4 that have not enough grip...
If you want responsiveness, start changing all that shitty bushings our car have.
My Fiat Panda has stiffer bushings.

As for toe, just re-read your original post, IMO 0.1 degrees total rear toe would be fine but I don't think you'll notice any kind of profound change really.
That's been my experience with this car, I've run both 0 and 0.1deg.
On other cars with heim joints and aluminum/delrin bushings, I've found too much rear toe (in excess of 0.3 degrees) to suck, bad, for everything, but 0 to 0.1 even 0.15 degrees no probs...

Losing grip suddenly and not progressively can be a characteristic of how the tire grips. Some tires have a lot of latent grip after wheelspin or sliding begins, and some have less. MPSS I had on the FD RX-7 were kind of the worst in this regard after 2 years on them, any amount of wheelspin and they instantly lost all lateral grip. Not progressive at all...

Dunno what you can get for more trackworthy tires, but you might consider something like RE71R, A052, RT660, ZIIIor if Michelin is preferred, Pilot Sport Cup 2?

RE bushings, I havent done much with my BRZ there, just polyurethane inserts for the rear subframe, which helped a bit with left/right transitions. Pretty happy with it as it is for street/track at the moment but may get poly front control arm bushings before next track season...

For what it is worth, I took "stepping on the gas" as basically going full throttle with the wheels turned. That is always going to cause the car to step out. If the car is too loose, feeding throttle while unwinding the wheel, then that is a different story.

Personally, I run about .16 rear toe in. My setup is 245/40/17 A052's on 17x9's, about -3.7 up front zero toe, - 2.2 rear, 7k/7k springs. And the car tends to range from really good to slightly too loose on corner exit. I've never ran 0 toe in this car, but I think it would be diabolical with 0 rear toe.

Thanks everybody, I found some experience even on the UK forum, and it seems that rear toe in is the culprit. I now have to decide if 0.1 or 0.15 deg per wheel.

I should add that my .16 is toe rear toe, so about .08 per side.

I wouldn't go over .1 per side.

Which translates to 1mm toe in per wheel

The Michelin PSS i ran always have this issue. Problem goes way when i run my 200TW tires. I accepted that it's just a tire grip issue and moved on.