Miata Front A-arm aligment relative to ground?

I am trying to model the Miata front subframe into a chassis drawing. I need to orient the suspension.

Does anyone know if thea line drawn through the two front lower a-arm pivot points would be parallel to the ground plane? Or is there some degree of inclination?

Guess I could ask the same for the back also?

I assume you are talking about the NA

At the stock ride height of approx 13.5" the lower control arms are angled downward (this is good for negative chamber gain). As you lower the car they will become more parallel with the ground. At appox 12.25" ride height the lower control arm will start to angle upward instead. This (and the lack of shock travel) is it is generally why it is not considered good to lower a stock suspension Miata more than about a 12.25" ride height.

When I switched to DP back in about '96 I relocated my lower control arms to give a chamber gain at a 12" ride height. see http://www.solomiata.com/images/rod-end-rear-control-arms.jpg

In reply to NOHOME:
OR, are you asking about the center line of the two pivot points of a single A-arm? Parallel to the center line of the car ? I have an NA manual that shows the dimensions to the underside of the unibody, which could be used to figure out the angle of the subframe. I just checked the angle of my NB lower A-arm with a magnetic level on the underside of the arm and it's very slightly nose down FWIW.

Deadskunk:

You got it. I have a nice flat chassis plate that I can measure against and I need to determine if the pivot axis for the lower control arm is parallel to the surface of the plate.

You mention that yours has a slight angle with the front being the lower. Does the manual give a degree value?

The diagram I was looking at gives the dimensions from a datum (your chassis plate) to the bottom of the Miata unibody at a bunch of different points, like where the sub frames would bolt to. That should be usable info to locate the upper surfaces of your subframes relative to your chassis plate. I'll have to look and see if the manual has data to orient the pivot points for the a-arms.

Thanks. It may be that the datums pick off other points on the subframe and the pivot points follow.

Would have been a lot easier if I had a miata to bolt on the plate and let the subframes fall where they might.

It doesn't appear as if there's any dimensions to figure out how to orient the subframes relative to the chassis plate except by locating the upper mounting points. Even that might be tricky.The dimensions look like they are given to the end of bosses welded into the unibody, so the length of the boss has to be added to the given dimension to locate the upper surface of a subframe. If you don't get it right I would think you would alter the caster and anti-dive on the front and anti-squat on the rear.

NOHOME wrote: Thanks. It may be that the datums pick off other points on the subframe and the pivot points follow. Would have been a lot easier if I had a miata to bolt on the plate and let the subframes fall where they might.

The whole thing assumes a straight shell and everything elsefalls in place. Without knowing how far any locating bosses protrude past the top surface you can't accurately locate that surface.
Anyone else got ideas or data to use? Keith?

OK. I've been out in the garage looking at my NB to see how the subframes are mounted. The rear is on 4 studs that are welded into the shell. If I've got this right the rear subframe is mounted with the front 10 mm lower than the rear.That's measured at the mounting holes. The distance from the front holes to the rear is 14.72 inches (374 mm). That's the easy one. The front is mounted on 6 studs and with two additional bolts at the very rear. The two front studs on each side are mounted 127 mm above where the rear studs mount (NOT the the rear most bolt).
The relationship between front and rear subframes will be critical, too. The front mounts of the rear frame are 309 mm above the datum. The front mounts of the front subframe are 290mm above the datum. That last dimension is the one I'm the least confident about. I can't tell if that is the distance to the end of the stud welded into the shell, or if it's to the flat surface the subframe rests against surrounding the stud..If you took the frames from the shell do you remember if the 1st,2nd, and 3rd points where the front frame mounts to the shell were all the same? If they were then I would assume the front two are 127 mm above the 3rd.

Deadskunk:

Thanks for going way beyond the call of duty. Going to take me a while to sort out the info as it pertains to my situation.

I did not start with a car, else I would have welded the subframes to the table and removed the shell in order to preserve all the relationships. Since I want the final product to feel a lot like a V8 Miata, only with an MGB body, I need to give this a lot of thought.