ZDan

I am tracking my recently acquired totally stock 2001 AP1 a few times this year. Did two days at Watkins Glen on 225/50-16 F, 245/45-16 R Kumho VictoRacers with the following alignment settings:

Front camber = -1.5*
Front toe = 0

Rear camber = -1.75*
Rear toe = 2x0.32* = 0.64* total toe-in

After getting used to the car (subtle steering inputs at turn-in!), I found it to be a lot of fun, if a bit oversteery. Felt like it was overworking the rears and underworking the fronts. The bumpsteer phenomenon was quite evident, as the car would give an initial oversteer LURCH, then would stabilize with general oversteer but totally driveable.

Then at Mosport I shared the car for two days (total ~4hrs track time on the car, yikes no wonder the following happened!). Day one, had to relearn the track, couldn't drive the S nearly as aggressively as my more track-oriented 240Z. Did well on day one, had a blast. Day two, the car became more and more spooky and less driveable. By end of day, a few Miatas were getting away from me!
Set a very poor time of 1:44. Benchmark 350Z, which I was 1.5 sec quicker than at the Glen was 4 seconds faster than me.

I didn't notice until I got home that the middle 1/3 of the outside rear was (ulp)corded! Should mention I drove from Providence RI to both the Glen and to Mosport on the race tires, so significant mileage on top of ~6hrs track driving.

Anyhoo, I just got a "new" set of shaved and heat cycled Kumho Ecsta V700's (the ones I guess they don't make anymore) in 205/45-16 F, 225/50-16 R. Not optimal sizing, but the price was right!

I'm considering reducing rear toe-in from .64* total to .48* in the interests of increasing rear tire life. But I don't want it to be an overly oversteery handful.

If this wouldn't cause a huge difference in balance at the track, I'll do it. Interested to hear input from those who've experimented with rear toe settings on a stock AP1 at the track, as to how much of a change is a BIG change.

Thanks!

Turn-R-Us

That does sound like a lot of toe in. I ran 1/4 inch total and was fine but tire wear was sig. I recently decreased to 1/8 inch total (.28 degree total). Will have to see, but I am tracking not Auto x. However I was running 255 with the 1/4 inch total. I increased to 275 with the decrease in toe, so hopefully the more rubber will keep it in check. You may need more rubber in the rear.

ZDan

I'm also tracking, not autoX.
Definitely would like more rubber in the rear, but class rules dictate stock width wheels, don't think I'd try more than 245s in back. What I really need is more rear camber, which maxed out at -1.8* (wtf?).

Hmm...

Zachreligious

I'd get under there and start checking parts. My car can get over 2.5 degrees in the rear. I'm not sure what the factory range is supposed to be, but depending on the rules, you may be able to modify the car to acheive at least the factory range of adjustment. I think that most SCCA classes are like that.

Is it normal to get less than 2 degrees in the rear?

Turn-R-Us

I depends also on how low you are. You can get more camber if your car is lowered. I am getting -2.8 in the rear and -2.25 in front with stock arms. I have heard people get 3.0 in the rear.

mxt_77

If it's the middle 1/3 that's worn, wouldn't that indicate over-inflation?

blackey

Also don't forget that the factory tires are closer to 205/245. The rears were specially made as a 225 but had a 245 section width.

Turn-R-Us

Yes middle is over inflation. But the best way to really know what you need is to use a pyrometer. That would give you all the info you need.

ZDan

FWIW, the inside 2/3 of the rears was pretty well worn down as well, actual cord showing in the middle, but you could "see" the cord under the rubber in the inside 1/3. Any case, the pressures were set to 32psi for the road, and ~38psi hot for the track.

IMO, the rapid rear tire wear is much more the result of significant (static, and particularly dynamic) toe-in, plus poor-from-the-factory F/R roll stiffness distribution.

Back on rear toe:
Perusing the forums, I found a source claiming .125" of toe-in (presumably .0625" per side) with 1" suspension compression for AP1's. DAYUM. Too bad a bumpsteer kit is illegal for me...

Anyway, running the numbers, I get
static .64* = .28" = .140" per side => .203" @ 1" => .265" @ 2"
static .48* = .21" = .105" per side => .168" @ 1" => .230" @ 2"

I'm thinking I'll reduce static rear toe to .48* (.21") total, as the percentage loss of dynamic toe appears to be pretty minimal.

But then again, reducing rear toe is going in the wrong direction regarding that initial oversteer "lurch" that I'm so not-fond of.

And I'm going to a track I'm not very familiar with this Mon/Tue, Mt. Tremblant.

Hmm...

Turn-R-Us

Most say to not go any lower than 1/4 inch toe total. Now if you are looking at degree it is a bit different. depends on the dia. of tire you are running. But to not complicate matters min around 0.13" per side to try to control the oversteer. The wear you are getting is due to your toe. I t is similar to what I got when I ran -2.0 with 1/4 inch toe per side. Then tire width matters and sway bars and stagger..........