Miata rear alignment

So, trying to plan ahead to make sure i can do what needs done.....

The car is my nb challenge car with a big six cylender in it, seam welded, 4 point bolt in roll bar, butterfly brace, frame rail connected, frog arms.

450/250ish springs on hard s bilstiens.

32mm front sway

Torsen

Rear sway:????

Ride height????

Autocross tires:sm7 slicks or avon medium compound 

Drag: hopefully wrinkle wall slicks

So, im ASSUMING drag alignment needs to be 0 camber and 0 toe in the back for max drag slicks grip. Autocross is an unknown. 

My background is all solid axle stuff, not independent. So having adjustable specs back there is actually harder for me since i dont know what i will need to do with it.

So, what do i need to set the back up to? Rough range would be awesome, as i know that this thing is different enough to need testing for finding the sweet spot. But knowing what range of adjustment i need to shoot for lets me know if i need to move mounts, extend arms, etc.

For autocross you can't go wrong with 0 toe and -3 degrees camber (if your bolts get you that far).  Unfortunately that will make your drag launch worse.  -2 degrees is probably fine and more in line with your factory control arms.

If you have the budget for the extended front ball joints they are the easiest way to get the big front negative camber you'll want.  Again, maximum camber, zero toe and your car should be good to go.

Like KyAllroad said, for autocross, you want little-to-no toe, and a ton of camber. My car currently runs -3.5 degrees in the front (I run offset upper bushings) and a touch of toe-out. Out back I run -2.5 degrees of camber and zero toe. Unfortunately, on the Miata, you adjust rear camber and toe via the same eccentrics, which means often your rear alignment can be a compromise. You might be able to get your rear camber where you want it but then your toe is way off, or vice versa. Paco Motorsports does make an adjustable upper rear arm that lets you just set toe with the lower eccentrics and camber with the upper arm.

For drag racing, I know some guys even go as far as running a little positive camber on IRS drag cars, with the idea being that if/when the back end squats, it forces it into 0 camber and gets the best contact patch. But, if your Miata is going to be any sort of lowered, good luck getting 0 camber, let alone positive camber on just the eccentrics.

RE the PACO adjustable upper rear control arms.  Due to the arcs of the suspension travel, they aren't terribly useful for quick "on the fly" alignment adjustments.  Basically you would change the camber and it would kick your tow out so far the car would be undrivable.  I had them on my CSP car and it was good to get -3.5 cambers but changing them required changing the eccentrics to keep toe accurate.

I'm surprised to hear they're changing the toe. I'm having trouble picturing how. In the front, adjustable camber will definitely affect toe. But in the rear, the upright is pivoting around the lower arm which determines toe and doesn't change at all. I'm really not seeing this.

So is much negative camber as I can get with 0 toe in the rear, as well as as much negative camber that I can get with 0 toe up front for autocross. Rear I want as little toe as possible as well as as little negative camber as possible in the rear. Correct? All the all also mention offset bushings, and he sources for these for a challenge friendly price?

Offset bushings in the lower arms have a tendency to self-adjust.

Easy to make, get a set of non-offset bushings and a chunk of steel rod that's the same diameter as the crush sleeve. Drill a hole in the rod that's off-center. Voila, offset bushings.

Since I daily mine, how much camber before you start really eating tires?

In reply to Justjim75 :

I have over 1000-miles & 3 autocrosses on my RE-71Rs with minimal even wear across the tread on all-4 corners. I’m running -3.2* rear & -4.1* front, but zero toe F/R. 

In reply to Justjim75 :

On a light car like a Miata you can run all the camber, but only if you're toe is close to zero.  Where you start eating tires is adding toe to the setup. 

Since jim brought tjis back up, he gave me a brainstorm. 

Set two alignments. Use a drilled index through the eccentric for easy trackside changes to the rear for the drags. Put a mark at both so i know what's drag and whats autocross. 

Wow. That's a good idea. You may have discovered a new way to keep the cams from slipping as well.

In reply to Dusterbd13-michael :

I ran mine with a half degree less camber on the rear than I could get on the front. Stock I could get 2* on the front, so I changed to extended ball joints to get 3*. Then I set the rear to 2.5*. For the drags I reset the rear to zero toe and camber. It just happens that my car ended up there by setting the adjusters in as far as they'll go, so resetting the suspension in the parking lot was pretty easy. I forget where I had the toe set for autocross, but it was toed out a little..

Cool, thanks all