Wicked Weasel

Does anyone have street and maybe aggressive street alignment specs. My new wheels and tires are going on this week so figured I should make sure the alignment is good before putting miles on the car.

thanks

SladeX

This is what I run for aggressive street/some track use. Mind you I also run a wider set stance of wheels which offset push the edge of the rim to the fender edges.
Front Toe Camber Caster
0 -1.3 7
Rear Toe Camber Caster
+0.05in -1.3 0.3

Fixed for incorrect symbol; should be toe-in, + positive value.

Wicked Weasel

Thanks

X25

Is that a toe out at the rear? I'd recommend the other way around (toe in).

SladeX

That's toe in. My bad. Should be a +

The car has a tendency to toe-out as it accelerates.

X25

I see; the shops here use positive for toe in, and same with camber.

Hmm, I thought it looked like the car toes in more under (rear) compression. I'll check that again next time the car is on the alignment rack. If it toes out like that, wouldn't it be very tail happy by design? These cars feel pretty planted considering all that power.

SladeX

Car is pretty stable under acceleration with those settings. It's quite the opposite of tail happy with those settings. The car in normal driving will catch itself quite nicely without drama if you push it hard. I've seen the traction light come on punching it on the highway at speed and didn't even realize anything was wrong until the traction light flashed and acceleration was interrupted only a little.

On track, it takes a lot for me to get to the edge of traction in turns. I usually drive in track PTR sport 2 mode since my tires are end of life for the rears.

When the car was stock from factory, it was downright terrifying. Punching it from low speed would kick the rear out hard to the driver's side. The traction control would flash but not before your car was 45 degrees. Turns out my rears had opposite caster setting in the back and opposite toe in/toe out for each side along with bad camber.

X25

Exactly, it's pretty stable in my experience, too, and I'd think it toes in under compression, which increases stability, not out?

SladeX

Under acceleration, it toes out.

This will produce zero rolling toe as the vehicle is being driven down the road because the natural tendency for the front and rear wheels is to toe-out due to rolling resistance and compliance in the steering and suspension.

https://www.aa1car.com/library/wheel_alignment.htm

X25

I'm not sure what to look in there, but we're talking about under (rear) compression (acceleration), and how it behaves depends on what the toe curve is, determined by the suspension design; I'm not sure I understand your point, or what am I missing? I think most sports cars toe in under compression, not the other way around.

SladeX

Being a sports car doesn't make it exempt from the physics of every car out there. Rolling resistance will always work against acceleration meaning that the more power you put down, the greater the tendency for the wheels to toe outward under power.

If the car naturally toed-in under acceleration, there would be no need for it to start off with a toe-in alignment, if anything it should start with a toe-out so that it could naturally toe-in. You toe-in the rear because under power, it will go to 0 and remain stable.

X25

I see, but I think what the geometry does under compression is more dominant here, unless you have so much play in bushings, etc. perhaps? I don't think this car toes out under acceleration.

Anyway, going back to alignment suggestions, that looks like a good compromise : )

SladeX

The geometry is nothing that special that it hasn't appeared on other cars before. Rolling resistance will always trump the geometry as the geometry doesn't want to upset the alignment as much as possible. If the alignment goes to hell under acceleration, this is because it's very very worn.

This was an issue in older cars; lift off oversteer comes to mind. Older porsches had this issue where your alignment was dependent on the power input. It would catch new drivers off guard because it would swap from understeer to oversteer because the suspension would shift so much that the alignment would change the characteristic of the car under power. This is NOT what we have happening on our cars.

As for my alignment specs; it's good for learning how to track your car while still providing good wear on the tires to last 8-10k street miles on sport cup 2 along with 5 x 30min track sessions on an average kind of track with lots of turns and braking. Note that I still have the grooves on the outer AND inner portion, and the wear indicator holes are still present in the grooves. I still have another track session in them. Replacements in my shed, but I will use these up on track 1 more time.


still on car with aforementioned mileage

ZR1Bob

I have two spec sheets, one for stock GM alignment specs and one from Pfadt Race Engineering. I used the Pfadt Performance Street settings when I aligned my car after installing new Michelin A/S 3+ZPs after the OEM Pilot Sports showed cords on the inside of the rears at 20,000 miles. The stock alignment I had obviously was not great. Always a good idea to get an alignment when getting new tires. -Bob