Tips for improving high speed stability?

[wizzurp]

My car is kind of a handful at highway speeds and higher, anything above 55ish and it just kind of does it's own thing. It likes to follow grooves in the road (it does this even at low speeds) and generally is just kind of darty. Im wondering if my wheel offset has anything to do with it, I've got some gay 15x8's with 0 offset, wondering if the increased scrub radius could be making it worse.
My alignment is:
Front:
L,R
Toe -1.4, -1.6
Caster 3.9, 3.8
Toe, -.01, .03

Rear:
Camber -2.0, -2.1
Toe .12, .08
Thrust angle of .02

Tire pressure is 40psi front and rear, front tires are much more worn than rears.

Please help me figure this out, it's not fun to drive when it wants to run me into assorted other vehicles endlessly.

[motorollow]

That is too high of a tire pressure IMO. Try lowering it a bit.

[wizzurp]

Ok, will do, tires are 195/50/15 kumho ast's for reference.

[OZMDD]

That's a horrible wheel/tire combo. You'd be better off with stock wheels on those tires, but I think the offset is more a problem than the width. How certain are you of the alignment specs? If they were done with those wheels, they might be accurate, but otherwise they are probably off. Toe adjustments will help a bunch with the tramlining.

Also agree that you are 10 psi too high on that combo.

[wizzurp]

100 percent sure, watched it be aligned two weeks ago. I figured the wheel offset wouldn't be ideal for sure, I have no problem changing that given I can find someone who wants them.

What would you recommend for toe?

Thanks for the serious answers, I'm used to seeing so many bullshit posts on here.

[wizzurp]

I took it for a spin at 30psi earlier, that alone helped quite a bit, certainly felt better for the long sweeping turn that I tried it out on around 65-70mph. It was also much less jerky/abruptly bumpy as well. Car still darts badly on my bumpy road though. I noticed it wants to center faster with this pressure change.
/assorted observations over.

[miataspeedracer]

If your specs above are correct, you've got toe OUT in the rear. That's gonna make your rear end nervous (pun partially intended).

Try for zero toe in front, and -.02 or -.03 deg toe IN on the rear.

[OZMDD]

Don't worry, the bullshit answers will come, you just asked the question too reasonably. Don't let it happen again.

1/16 to 1/8 total toe-in up front will give it a much more stable freeway ride and cut down on tramlining. I like zero rear toe, but other folks are more familiar with NA alignments than I. Did you know that you can measure toe using your foot, as the increments are based on the driver's big toe?

[sammm]

Those AST's are all-season rocks...had a set, not a fan.

[wizzurp]

The rears are toed in, not out, a negative number is away from centerline of the car, positive is towards the center for that machine.

Yeah I the tires aren't ideal, they were what I could afford at the time though, when I got the car it had 205's out back and 195's up front, that seemed to help with traction.

I had the rear toed in a decent bit because its supposed to help keep the back end in line with extra power, seemed to have helped. I'll have the fronts toed in and try again, hopefully that'll help. New front tires will probably help as well as the old ones are pretty worn.

[Jwett9]

http://basscode.orconhosting.net.nz/...tor_camber.jpg

[wizzurp]

Nudged the left front in slightly and that helped quite a bit. Probably not quite 1/16 total but it was enough to help quite a bit. That plus the pressure change made a big difference. I think replacing the front tires will be the final step. It felt good on smooth curvy roads, it just wanted to go faster.

Does a splitter make a noticeable difference at highway speeds? I've been considering building one, just wasn't sure if it would be worth it.

Thank you very much for the tips guys!

[trickyrix]

I think the gay wheels are the biggest part of the problem. I run zero toe all the way around and my car is rock solid at high speed. As for the aero, I swear I noticed a little bit of improvement when I added a factory R-pack front lip several years ago, but that might have been wishful thinking...

[jrj512]

Does a splitter make a noticeable difference at highway speeds? I've been considering building one, just wasn't sure if it would be worth it.

You should not need a splitter to have stability at 60 MPH on a highway. Unless, of course, you're in VTEC, yo.

[wizzurp]

I should have stated highway speeds and up. My car gets there fairly quick.

I'm starting to think its time for some higher offset 15x8's.

[Jiggerachi]

What suspension are you running? When I bought my car the blown oem shocks made the car float all.over.the.road at higher speeds. This was across both 14x7 all seasons and 15x7 azenis. Changing the suspension made it track straighter even before the allignment. It wasn't necessarily darting, but a general floaty feeling, strait or lane changes were not confident feeling at all towards higher speeds.
Switching to +25 offset 15x8s later made it wander over bumps a little but not bad at all.

Not an expert in anything other than what little experience I have but FWIW.

[Rogue]

Ricelands?
Your wheels are 2" too wide for your tires, but if you need that "baller stretch"....deal with it.

[OZMDD]

Yeah, if you're gonna run 8" wheels, get 225 tires. Problem solved.

[wizzurp]

I've got tein flex's, and yes, I'd prefer 225's, I'll have to see what is available in my price range when it's time to get a new set. No I'm not looking for stretched tires, just happen to be the wheels that I have currently.

[altiain]

I think you've hit the nail on the head all by yourself.

I've got some gay 15x8's with 0 offset, wondering if the increased scrub radius could be making it worse.

Car still darts badly on my bumpy road though.

The problem is the wheels - more specifically, the problem is with the extreme change in wheel offset. You've fucked up the scrub radius (made it significantly more positive) on the car. That's why it feels okay on smoother roads, but the front wheels want to jerk the wheel out of your hands on bumpier roads.

Here's a couple of good links that give a basic explanation of steering angle inclination and scrub radius, and the effect of wheel offset on both:

Link 1

Link 2