Hi all,

I'm looking for some advice from those running track cars on best steps to alter my handling balance.

The setup;

AP1 chassis
Tein circuit master RA single adjustable coilovers, set to mid of adjustment front and rear
10k springs front and rear (w/helpers)
early AP1 front bar
NC Miata rear bar
urethane bushes all round
spherical adjustable camber upper front arms
megan spherical rear toe arms (set one spacer from bottom on outer rear)
steering rack spaced up 16mm
235/255 Yoko A048 on 8's and 9's
-3 front camber 0 toe
-2.25 rear camber 1/8" total toe in

symptom; Car over steers under full load cornering (power on) past the apex, and when it goes it goes pretty hard, usually a spin. The car will also oversteer trail braking but typically easy to correct. It never under steers. I'd like the car to be more neutral under full load, even a touch of understeer, so I can really trust it.

Suggestions on what to adjust first, or recommended steps?

Cheers,

Earlysport

 

Go white line or stiffer front bar and/or increase rear to 1/4" total. You can also play with reducing front rebound or increasing rear compression (to press the inside rear tire into the ground on corner exit throttle)

 

soften the front dampeners

 

Tire pressure too high in the back? Whatever you start to adjust, do one thing at a time and test it.

 

My AP1 handled best with the stock rear toe-in.

A softer rear or firmer front will help. Try softening up the damping in the rear first since it's free.

Remove one rear sway bar end link and see what she does. Again, it's free.

Your square springs are stiffening the rear and contributing to the looseness.

Many of us run really big freakin' stiff front bars.

 

What's your ride height? Consider running the front end higher then the rear, it will shift weight to the back and help plant the rear of the car. Reducing the damping adjustment in the rear is a good first easy tip to try first. You already have a pretty wide sway bar bias with the 00-01 front bar and miata rear bar, id be a little hesitant to go more extreme, yet.

The factory rear diff is under 100% lock up on both wheels in your corner exit scenario, id expect your symptoms there, this is where throttle application just has to be modulated - driver mod) Or move to a lsd type rear diff. Corner entry oversteer can be as simple as a few damping adjustments, or again driver mod) more rear tire is always a great way to address lack of rear traction, however there are limited options there.

What ever you choose to try, one change at a time is good advice.

 

On a typical single adjustable comp/rebound coilover, that would create the opposite effect. Causing nose of car to compress quicker, shifting weight forward, causing rear to lighten up and come around easier. Not the direction the OP is shooting for. If anything he needs to add damping up front and remove it in back. Right now he is running even damping front to rear.

Doing this change effectively adds resistance up front and removes it in the rear, allowing the sway bar bias to work more for him. This is only under quick transitional handling, not steady state, but can be enough to allow the driver the added bias control he is seeking. Sounds like corner entry and exit is an issue, so this would work in my experience.

 

keep the toe in, stiffen front bar, soften rear dampers, lower ride height in rear, increase rear camber.

Btw you didn't mention the speeds the tail is coming out at

 

sorry thought he said it was pushing not oversteering, derp.

 

I don't really agree with the LSD advice. Going from a helical diff to an aftermarket clutch diff will definitely give the car a more oversteer/high rear slip angle corner exit behavior. It's very consistent on the clutch type diff because it locks up based on torque input. The factory helical biases based on torque available at the rear wheels, so you've got to make sure you're not running into travel issues back there (I doubt it based on OP's setup).

I've gone between a factory S15 diff (basically same design as S2000 diff, same vintage, and probably same supplier) and a Cusco RS, and the RS is was definitely much more oversteer prone at pretty much any setting of lockup and preload.

I would say more toe-in would help the rear, as OP is running half OEM spec. If you want to run that little toe-in, you might need to tweak your toe arm spacers to get less bumpsteer in roll and squat, and actually measure it.


I would also ditch the urethane bushings - too much friction in the joints, which will make the car less compliant on the tiniest of bumps. They're probably one of the worst things you can do to suspension bushings IMO. They feel fine right after you install them, but a short while later the friction is through the roof.