Hi Guys, new to the forum..
Thought I would post here since there seems to be more track wisdom here than on other miata "track" forums..

I been struggling with turn in understeer for the past year, which as you know is a no-no on a car with no power..(scrub off speed). The situation got a little better when I upgraded from the stock rear sway to a 15mm sway and put it on full stiff, however the issue is not completely gone.

About the car:
99 miata ~ 2300 lbs with no driver.
15x9 wheel with 225/45 RA1's
Xida's on 800F/500R
RB big front sway bar soft setting/ 15MM rear on full stiff
Power ~ probably around 120 whp
No aero

I am not really trying to throw money at the problem. I know this is either an alignment issue or a height issue- however... I am as low as I can go in the front - as is car will rub on the shock mount / tower.

Alignment:

Front -3 Camber, 0 Toe, max castor 5.5
Rear -2.7 Camber, .1 Toe

height:

4.5 inch front/ 4.75 rear

What do you guys think?

 

How is it in steady state? Do you feel you could safely shift your roll couple rearward (ie: softer front springs/stiffer rear)? Have you checked for bumpstop activation with the zip tie test? Is it corner balanced? Is that 0.1 toe in or out? What tire pressures do you run? What's your weight balance?

Is this a pure track car, or a dual duty car that requires some forgiveness on the street? If it's a pure track car, you could try toe out in the front, or zero toe in the rear. Or even a smidge toe out in the rear. A quick temporary solution to see if roll couple is the issue is to play with tire pressures. Stiffen the rear a bit.

 

The car has a near 0 tendency to oversteer on track (autox diff story).
I have not checked bumpstops, but wouldn't be surprised if they are bottoming out, and be willing to raise front a smidge.. however that will lead to a loss of front camber as its maxed out at -3. Car is not corner balanced.. that might be the solution.

I have played with tire pressure. I am usually in mid 30's and played with +/- 3 psi front to rear and vise versa. No noticeable change.

Toe. I forget which is in/out . in the print out it says +.10 a side

 

Lower the front end 0.25". All 225/45-shod Miatas rub the shock towers, that's normal. With a 900# front spring there's no reason why you can't get down in to the 4.1-4.2" ride height range in front, especially with an NB front subframe.

If that doesn't work, I would be inclined to try a set of 800# front springs.

If your tires are very old (2+ years), that will also cause understeer.

 

Typo- fronts are in fact 800lbs. I will lower the car a little in front. I'm in the process of pulling a little weight from the car, 30-40lbs so they should help if it is indeed bottoming.

 

You can also try softening the front shocks settings some especially if dbl adj soften the compression, should help initial turn in.

 

I see go lower has already been mentioned. The other glaring error, at least to my eyes, is zero toe. Put some toe out in there in the front.

 

0 toe does not cause understeer, adding toe to a car that understeers is a bandaid fix, don't do this.

 

It's not necessarily a band-aid fix. Toe out is often good in the front, and promotes good turn in.

 

I agree with Sav about the toe out being a bandaid. Lowering the compression on the frt shocks won.t lower it but it well let the weight transfer to the front when you brake just before turn in. If your front shocks are set to high it well DELAY the weight transfer forward for turn in. If that doesn't do it try what Sav suggested about lowering the front some, I run 4" up front with 245 on 10" wheels.
Also is the front bar a 1 1/8" hollow bar?

 

Or: How to Trail Brake | Driver 61

 

Toe out scrubs off speed also, trail braking is also a bandaid fix. Both of these are used as a technique for certain corners or tracks. They are not ment to be a means of getting your car balanced. If your car won't turn in there is something in the setup that isn't right.

 

How freely does your front sway bar move?

 

+1 for front toe out, I´d start 1mm per side. If it´s faster, who cares if someone calls it a "band aid".

 

Somethings not right here...Because of your coilover setup I would quickly "suspect" you have a corner weight issue, if you dont have scales, beg, borrow, or steal some. Or I would suspect driver inputs, have any video?

For the racecar I always run a hair out in the front and dead zero in the rear. However, anytime I have run the rear bar on full stiff, the *** end is always sliding around and understeer is the least of my concerns.

After the initial turn in problem, does the car continue to understeer or does it balance out?

 

I will lower the car two full turns of the collar.

 

swaybar moves freely- ive checked it.

 

I will run o toe in front and rear. I think the key here is lower front and get car corner balance. Will report back.. 1 more month until first event of year!

for reference is "toe out" a "+" or "-". ?

 

Corner balance, 50/50 cross weight what about front to rear?

 

Corner weighting is LF to RR TOTAL should be same as RF to LR and alignment and ride height has to be done at same time as changing either well change corner weighting. If the car pushes turning in both directions, I doubt its corner weighting. If you can get it corner weighted and aligned all at the same time I would but lowering the front is where I would start and go from there, one thing at a time. If you go through the expense of corner weighting and alignment and it doesn't correct turn in and you change something else after corner weighting you pretty much wasted time and money.