Locating a Miata subframe?

I am considering using a complete Miata rear subframe hub to hub in a different chassis. The front suspension will be stock to the chassis (not Miata). I will have complete freedom to locate perches, subframe, etc. 
 

What's an optimum height to locate the subframe in relation to the suspension?  I am thinking with the lower A-arms parallel to the ground, but figured I'd check with the hive. 
 

Alternately, we can talk about distance from the center of the wheel hub to the fender lip- I can convert it. (That one is probably 12.5"- 13")
 

Use will be autocross and aggressive street handling. 

I'd check the angle of the arms at rest on a stock Miata, that should give you a good place to start in terms of suspension geometry and then you can choose the height of the subframe to the chassis to suit. You might want to adjust the fore/aft tilt of the subframe to take out some anti-squat, if it has any. Ideally you'd want to ignore fenders and modify them to fit as an afterthought.

In reply to GameboyRMH :

Yep. Fenders are a non-issue. 
 

But it's how Miata guys talk about ride height. 

The easiest place to locate one is by looking under a miata

Ba-dum tiss

i'll be here all week, and for the next several, don't forget to tip your door dash driver

It's how Mazda talks about ride height, some of the other Miata guys use frame rail height. The latter can be very precise as long as you are using a new tire of a specific model and size and have a given tire pressure. Hub to fender has the advantage of being much less dependent on outside variables.

Parallel lower arms are a pretty good ballpark. That's what I used on the MG. The Miata doesn't have any truly evil camber curve problems so you can get away with a bit of variation. Almost every Miata running in autocross or on track has the lowers going up to the wheels.

Hey if you need one, I got one sitting on a shelf thats gotta go.  

In reply to Apexcarver :

Nope. I've got one. Just thinking through the next few steps on a car with no body, and no idea what it's finished weight will be. 

In reply to SVreX :

It sounds like the measurement you're missing is the distance from the ground to the stock Europa frame at the rear of the car. If you need that I can possibly either get it from the owner of my old one, or put you in touch with him.

In reply to Pete Gossett :

I can get that too. 
 

I'm more interested in that info from a modified, highly competitive car than from a stock one. 

Supermiata guy has some info. You will have to cross reference it to a stock Miata though.

Supermiata guy (aka Emilio) likes pinch welds because he's basically running a spec series where I tend to have to support a wider range of applications :) But it's good info for sure, I've been using his alignment recommendations for years on my own cars.

If you want to translate, you just need to determine the distance from the pinch weld to a datum on the subframe. But he's also stuck with certain limitations, such as the location of the subframe in the chassis. If you lower a Miata to get a lower CoG or less aero drag or something similar, you may be sacrificing the suspension geometry to do so. You're certainly sacrificing compression travel at least.

I'd be tempted to position the subframes where the factory put them at stock ride height, as that's what they determined was the best. Then drop the car down lower around them. Which, again, is what I did with the MG.

In reply to Keith Tanner :

Makes sense. 
 

Finding the various reference points and datum is easy. I have a Miata, and a laser. 

In reply to SVreX :

I've got a dimension sheet for an NA that shows all the dimensions to locate the mounting points for the subframes. IIRC, it uses the bottom of the Miata frame rails as the datum.

In reply to DeadSkunk (Warren) :

Mind sharing it?

In reply to SVreX :

Not at all. I can try scanning it and email it to you.

Let me see if I have a digital version.

Edit - I do, give me a few minutes to extract. Thanks for the reminder that this was in the manual.

SVreXPaul at g male

View in separate window for higher rez. Let me know if a higher rez is needed , I have PDF. FYI, this is in the factory service manual.

Keith, that's the same diagram I have.

Paul, note the mounting points for the rear subframe...it tilts forward by 10mm.

Edit: I take back what I said about the datum, it does appear to be from the road surface.

Ah, there's a third page with the identification for the side view. I'll have to upload that tomorrow.

Thanks!

Im working off my phone. I'll have to look at those in a couple days