Hey All - wasn't sure the right place to put this, but I'm assuming this is either a braking or suspension issue. I bought my '02 Miata about 2 years ago. Every since then, during track day events, I've noticed that under heavy braking the car nose dives as expected but then starts to pull to the right, such that I naturally countersteer to the left to prevent this. I've done at least a half a dozen track day events and assumed something was up with the calipers or uneven traction from tires. Fast forward to today and I've replaced the SE brakes with 4 piston wilwoods, I've replaced the tires with brand new RS4s. The issue still happens. In this same time I also upgraded from Koni's to gen 1 Xidas. I also have FM front rear sway bars. There are a couple of things definitely left unaccounted for:

First, an alignment. While the car drives perfectly straight on a flat road, I'm sure that doesn't tell the entire tale. Second, tram lining seems to have increased with my RS4s (245 width) and I'm wondering if this is actually the root cause. The front sway is on the middle hole and the rear is on full soft (I get a ton of rear end instability in highish speed turns that I was trying to account for and this did help). Lastly, I suppose also I haven't had the car properly cross weighted.

Anyhow, has anyone else delt with this and properly dialed it out? While it definitely makes heavy braking zones more exciting, I don't know that I necessarily want it for this particular part of hard driving!

 

I'd check alignment before anything else. My car was doing something similar at my last track day, darting under braking, fine in a straight line. One of my front eccentrics had slipped giving me excess toe-out on the side it was pulling to.

 

Alignment has a big effect on how these cars handle. Did you have it done before and/or after the suspension change? If so, what kind of numbers?

Not related to your braking issue, but I found the big FM rear bar to be an impediment to handling balance on my car. Even with a conservative FM-recommended alignment that has more rear negative camber than front, I found that the car oversteered excessively on the track. If you're going to be realigning anyway, I'd suggest ditching the FM rear bar and looking at one of Supermiata's suggested alignment setups, especially since you're already running their suspension. Personally, I haven't bothered to get a new alignment yet, so I set the front bar to soft and went back to the stock rear bar. That's not ideal - it's now a little on the understeering side of neutral - but it's far easier to manage the rear end that way.

 

You’ve done all this work and never had an alignment? Definitely start there. Some cars have bump steer depending on what knuckle/tie rod combo they have. If one side is worse than the other, it can increase toe in or out (depending on what side it’s on), and pull the car in that direction. Some alignment centers will know how to check this, others won’t, just an fyi.

also at this point, Miata bushings are 20-36 years old, and need to be replaced if tracking. Not sure if this has been done to your car or not. Getting an alignment dialed in perfectly for your setup is largely pointless with stock bushings, so I’d address that first.

and lastly, actually before any alignment, lift the car with the brakes off, and shake each wheel left/right and up/down. Up/down play in the front is ball joints, right/left is tie rod, both is wheel bearings. Have someone shake it while you put your hand on each joint to ID where they play is if you feel some. Lots of bushings in the rear, so if there’s play, it’s a bushing or wheel bearing.

 

Yeah sounds like bump steer, specifically your caster affecting alignment under weight transfer.

 

You did Xidas and no corner weight and alignment?
Could very well be a caster issue. Or bushings or driver?
If your doing track events are you pads wearing evenly?
Corner weight and alignment....

 

Yes - i got gen 1 xidas while the car was down for a motor swap. I've only done one track day since the brake change, but my pads did wear evenly before. I'm planning on a sebring on April 4 and there's a shop around the corner that came highly recommended to corner weight and align at.

 

Just make sure they ballast the driver seat for your weight. Sounds obvious but you’d be amazed what gets missed sometimes lol

 

+1