NTMD8R

2014 Convertible, Z51, MN7, MRC

We autocross a lot (25 events this year).
Of course, I can't just leave the car alone... I have to "improve" it.

So first, I just lowered it on the existing bolts.... about 5/8".
Fine.
I ordered wider wheels.... 19x10 front, 20x11 rears.
But it takes 4 months for them to arrive.
In the meantime, the stock tires are really great when it's warm,
but pathetic when it's cold (as GM and Michelin have said).
So I order Toyo R888 tires... 265x35x19 front, 285x35x20 rear,
and install on the Z51 wheels.
Better.
Now I want to try better sway bars, to reduce body roll, and (hopefully) make the car turn better.
So I get the LG motorsports G7 bars... much stiffer, and the end links
make them adjustable. Set them to about mid point to see how things go.
It seems better.
Finally the wheels arrive.
So I now get Toyo R888 295x30x19 front, 315x30x20 rears.
Whoops... now I get major rubbing on the fender lips... but only from
undulations in the roads.
So I raise it back up (on the stock bolts) by about 5/8".
That seems to have fixed the rubbing.

Alignment:
Front -2.5 Camber, 1/8" toe out
Rear - 2.0 Camber, Zero toe (I can't get any more camber).
I need that much rear to get the tires to contact across the whole tread.
I have removed the washers from all the A-Arms.
Pressures (cold): Front 30, rear 25

Now I am now getting severe oversteer.
I can go around tight corners quite well, but long sweeping curves,
it will spin out if I try to go too fast.
So, tighten up the front bar as much as possible and loosen
up the rear bar as much as possible.
Better, but still quite a bit of oversteer.... long sweeping curves just aren't fast.

So I have replaced the LG rear bar with the OEM rear bar.
My next event is Oct 25, and I'll see how things go then.

My next thoughts are to
1) replace the rear bar with a non Z51 bar
2) remove the rear bar altogether
3) replace the front Z51 spring with a Z07 front spring (about 35% stronger than Z51)

So..... I would really appreciate any thoughts, comments, suggestions, even bad stuff....

I would really like this machine to go like it's on rails.
Those friggin Miatas (I run with a bunch of "tin cars") are killing me.

fatbillybob

What tires are the miata on? R888 is the worse tire I have ever tracked...once. Also, written sidewall size is not always what you get in real life. It is possible an other tire brand might work without body contact. You can also tune over/understeer with chassis rake. Also why not 1/16th" or rear toe in? Does this chassis have any rear bump steer? Have you pulled the rear spring and measure the bumpsteer?

NTMD8R

Miatas are on A6 and RE71R.
R888 tires are a bit narrower than most other brands.
Anything wider and I WILL rub.

I could try some rear toe in.... this is the kind of help I am looking for.
I have not pulled the rear spring, nor considered bumpsteer.

I am using R888 tires as a compromise.
We did 7 or 8 years of trailering wheels and tires,
and now we just want to arrive and drive.
So, yes I know they are not the stickiest, but over the 5 years I've used them,
they are actually quite good for autocross.

flyby763

Add toe in on the rear alignment

acrace

I, too, would suggest adding rear toe. The beauty is that it is easy to do between runs, so you can get a direct comparison of what changes does.

On my C5Z and C6Z, I've had anywhere from (approx) 3/32" to 3/8" of total toe in, depending upon the surface, tires, tire condition,a don the rest of the set-up. All on V710s and A6s.

acrace

Also make sure that the rear bar rotates nice and free (zero bind).

69autoXr

My comments are regarding your sway bars, because a few of your comments lead me to believe you are not adjusting them correctly, or you're confused about how the adjustable endlinks work.

First, the endlinks are adjustable to be able to set zero preload on the bars so that your corner weights aren't jacked up when you connect the bars.

Second, the bars themselves are adjustable, and have multiple mounting holes for the endlinks to vary the length of the lever arm of the sway bar. A quick google of the LG G7 bars seems to show that the rear is adjustable (3 holes), but the front is not (picture shows only one mounting hole for endlink). You would vary the sway bar stiffness by adjusting which hole the endlink uses, not by tightening or loosening the links themselves (this is what I read from your post, perhaps my interpretation is not correct but this is how it read to me).

Sounds like you need to try the rear bar in a softer setting, so place the endlink in the hole farthest from the bar pivot point. This gives the bar a longer lever arm and makes it softer.

NTMD8R

69 autoxr,
The pictures on the LG site regarding their G7 bars is incorrect.
The front bar has 2 holes, the rear bar has only one hole.
You may be correct about me not understanding how they work....
I did think the adjusters were to also provide some adjustability with respect to roll stiffness.

In any respect, I have now replaced the rear bar with the OEM Z51 bar, and we'll
see how that pans out.

The next thing is to put some toe in to the rear alignment.

If that all doesn't do what I want, then next.....
Base rear bar
No rear bar
Z07 front spring

fatbillybob

Chassis rake is also a good tuning tool.

Bad Karma

I haven't run R888, but by your front pressure you may be a little low in the rear. I know when my pressures get too low the car slides around a little. Or maybe lower the fronts a little. If everybody else is running that much pressure difference front to rear on the R888, then just ignore me. I'm usually only a couple psi difference front to rear.

But like the rest said I really like the feel my car has with the rear toed in.

l98tpi

I would toe in 1/16th or 1/8th, -1 neg camber, and corner balance the car. Not sure about your tire pressures but best way to find proper tire temps is to measure temps after each run or couple laps.

spdislife

Agreed on adding some rear toe. My car is an 04 Z with T1 suspension. I ran the R888s for a year and a half on stock C5 Z06 wheels, and to maintain a good balance I used cold pressures of 26 psi front and 27 in the rears.