Easily with a cool down lap, excessive time before making measurements, and improper measuring procedures.

Magic, no. But it's REALLY easy to have greatly varying results from even the most minor changes in processes or consistency. ...therefore it's easy to draw wrong conclusions from bad data.

Depending on the car and tire, 20-30*F spreads are a good range for 95% of situations.

 

Ideally, you want to try the extremes of any adjustment range and see which is better.
Working by myself, with limited track time, I generally end up just trying to work on the nut behind the wheel instead.

The one thing you need to be careful about is that you actually go with what's fast, though, and not what feels good!

Lol. I want to try lowering it a bit more, but I can barely get a jack under the car as it stands.
I can only get the car in and out of the garage with some special wooden bridges I built.

 

I just installed some aftermarket adjustable sway bar links, since my (probably) 30 year-old stock links were totally slopped out, and the current price of ONE stock link is more than the price of two aftermarket pieces.

I pulled on the bar a bit to see if the sway bar mounts would flex, and they of course obliged....

I wonder how much there is to gain by going to billet sway bar mounts.

There's a company that makes some extended rear mounts that let you invert the rear sway bar links. This apparently makes them work better, and also makes them easier to work on.

I also went ahead and ground down my rear UCAs to keep them from smacking into the shock yoke. I don't quite understand why that little protuberance existed in the first place.

I was doing some research on the stock sway bars, and it turns out the rear sway bar rates range from approximately 1 kg/mm to more than twice as stiff at 2.3 kg.
Ref: https://minkara.carview.co.jp/userid...7768/note.aspx
At least for JDM models. There seem to be four different versions of the rear bar (compared to just two for the rear bar).
Given the prices of used FD parts here, buying a full set of rear bars would probably be a pretty good investment for suspension tuning.

The front bars only vary from 8.6 to 9.2 kg/mm, apparently.

 

I bought some toe plates on a whim, and it seems my front tie is -19 mm...
That might explain some of the things I am experiencing.

We had to do a bit of guesswork regarding toe after I had my steering shaft welded and didn't put it back on straight.
But I didn't think we were off by quite this much.

 

LOL oops

While you're at it, check that you have similar / same amount of range available when turning full left and full right with the steering wheel straight

 

We did check that, since I got it wrong at first.

I managed to get the toe to about 1 mm out after two tries. The toe rods have the same amount of thread showing on both sides, but I’ll probably need a proper alignment to get it perfectly straight.

I’m probably going to need new inner tie rods or something, since there’s a knocking sound coming from somewhere.

 

I did an all-rotary trackday at the same course I drove last time.

I went 0.2 faster this time even while driving less hard, and went about as fast as as by PB fairly consistently, but I was using a bit more of the track (since I was given explicit permission to do so, haha).

I was the fastest stock-body FD that day...

I noticed that my handling differs significantly when turning left versus turning right. I assume it's an issue with my crossweight, since I'm quite heavy, and I don't have a passenger seat in the car.

Wish I had easier access to a set of scales, or at least one of those old-fashioned lever-type scales.

 

Crossweight, camber, toe, caster could all contribute independently or together. Scales take some effort just to setup let alone use successfully. Might want to pay someone to do it if you have a trusted source. I typically do the corner balance together with the alignment.

 

There is exactly one local shop (that I know off) with scales and an alignment machine, but not being street legal, it's a painfully expensive process...
I also know someone who owns scales, he just won't let me use them...

However, I am worried that corner weighting will make my wonky ground clearance even wonkier (the right front corner is about 10 mm closer to the ground than the left for some reason).

 

Speaking of the topic of this thread, I took a look under my rear fenders, and noticed that I have probably less than an inch of rear stroke before I hit the bump stops.

This is more or less at the default settings provided by HKS.

However, at my current ride height, this is enough stroke for the tire to scrape on the wheel house (on one side) and the upper arm to impinge on the shock yoke.

So I wonder if I shouldn’t add a few mm of preload and add a bit of rake to the setup for the stroke and aero benefits.

I also noticed my rear sway bar is quite a way off parallel with the ground.

 

try it and see what it does! changing the rear ride height changes camber and toe at the same time, so it should do something.

 

That's what I'm worried about!
I remember the last time I had rake in the car, it made it very squirrely under braking, and I ended up taking out quite a lot of preload.
That was a long, long time ago though.

 

I was able to do a string alignment at the track yesterday.
My front and rear toe were both pretty off...

The toe plates I bought aren't anywhere near accurate enough.

With my new splitter, an alignment, and cooler weather, I went two seconds faster.

There was a bunch of FDs at this track day. Like, a comical number.
One of them almost burned down during the "it's not a race" race. I saw the driver suddenly decide go to the pit lane, and it suddenly burst into flames and sparks under the car.
The fire was put out fairly quickly, but the body kit got pretty toasted.

Mine almost burned down, too, since the downpipe came unbolted from the turbo about four laps in.

 

I should also mention that this was the first time I have ever felt the stock brakes were inadquate. I couldn't even get a hint of a lock braking on the straights despite using way more brake pressure than usual.
That's probably where a lot of my time gains came from.

 

I would test out raising the ride height to try and gain some suspension travel. Especially in the rear but maybe by a similar amount all around if it was feeling squirrely under braking. Just make sure to recheck toe afterwards - using the string method so you know the car is square.

I had to raise the rear on my Spec Miata to gain more travel and more easily put what little power we have down. Was bottoming out coming out of some corners on some tracks / corners. That was before we switched to Penske shocks.

The braking sounds odd. What pads / heat range are you running? Have you bled them recently? Maybe check rotor face for any glazing.

 

I think I could get more stroke in the rear without changing the ride height by increasing the preload just enough to make the helper spring sit a bit higher, and then shorten the length of the shock.

I wonder if maybe my sway bar being popped up isn’t limiting rear travel as well. I’ll try unhooking it, and if it makes a difference, I’ll get adjustable links.

I think the braking thing is simply improved grip levels due to the splitter. I’m able to brake later and harder. I could probably still lock them if I tried. I can still lock them in slower corners.

They’re Project Mu 777 race pads. I used to use 999s but I thought I needed a bit more finesse.

 

Looking back at the data from HKS, I think I did have the rear too low. You're supposed to have the rear fenders a smidge higher than the front, but I actually had it lower than the front.
That may explain why things were hitting/rubbing, and why the sway bar was at such an acute angle.

I cranked on a bit of preload in the rear so the shocks weren't so close to the bump rubber, and played with heights to get everything within the ballpark.
Now, the sway bar doesn't look like it's going to run out of travel, and the shocks have a bit more free stroke.

It was, to put it extremely mildly, a lot of work. There's a lot of tail chasing involved...
The fender heights are reasonably close, but the pinch weld and subframe heighs are a litle wonkier than before. Oh well...
I still have to go back and tightening everything down, reattach the sway bars, and get an alignment.

Next time, I think I'll just pay someone who knows what they're doing.

 

Setup is time consuming. I generally allocate 2 days to do a corner balance and alignment on my Spec Miata. Partially because I'm slow, partially because I don't do it frequently enough to do it quickly, lastly because I want it as close to perfect as I can.

Sounds like you're doing well though. And taking the time to learn and analyze and get it right.

 

The main problem is that it’s a nearly 30 year-old car that’s been wrecked multiple times, so there’s no clear source of truth to measure from.

The pinch welds, fenders, and subframe don’t agree with each other, and measurements have a significant margin of error. Especially on the mangled rear right pinch weld.

The second problem is that changing one corner changes all the other corners.

I think I finally have it where I want, with the fenders and pinch welds roughly even. Though my intent was to have a slight rake…

 

Yep. Same with my Miata regarding reference points for ride height measurement. Some people resort to other reference points like the lowest points of the subframes. AND... you have to measure on a flat surface - which doesn't exist unless its your corner balance rig.

In my opinion, the ride height measurements are secondary. They are a good starting point to get the ride height set and the suspension placing the car "evenly" on its tires with driver weight in the car. From there, the act of corner balancing is going to change the ride heights slightly. Setting corner balance is a slow process where small changes are made at each corner to arrive at the end result. Time consuming to do it right... You need patience to do it. Which means it can get expensive to pay someone. Especially if they aren't familiar with the chassis.

NA and NB Spec Miatas tend to sit high on the right rear because that is the lightest corner of the car. Looks goofy but not super relevant for a race car.

 

I can’t imagine doing it without hub stand.