Front and Rear Subframes
 

Is there an advantage to running either the NA or the NB front/rear subframe in a Miata? I've read that there were changes, but nothing that specifically says one is better than the other or the factual reasons. Most posts were just about making sure you have the proper steering rack if you do the swap. Besides that, what are the actual differences and which combination is preferred and why? I have access to two complete setups and need to decide which way to go.

Ive heard that the NB miatas sub frames had different control arm mounting points that offer a better suspension geometry.

I know the NB has better geometry for the lower front control arms, but I believe the rears are identical.

good to know

rear nb subframe is 5mm wider. 01+ nb subframes have threads for the subframe braces. Also newer bushings :-)

Guess I'll be swapping them out in the next couple of weeks.

Thought the width came from the spindles?

the steering rack mount is different too.

why are you swapping them out dont you have an NB?

Right now I have an NB and an NA, but I plan on putting the NB up for sale in a few months. Just trying to build the 93 using the smartest combination of parts. I also think it might be easier to swap the subframes/steering rack than to move the suspension, brakes, axles and diff over piece by piece.

Mounting points for the sway bar end links are stronger on the NA

Nope.

The NA and NB subframe and the arms have the same geometry. The NB uprights place the hub 5mm outboard compared to the NA uprights. The NB axles are 5mm longer to compensate.

I have NB axles in my NA. Why does my car still roll?

There are a number of differences.

Up front the NB front lower arm is mounted slightly higher on the subframe. The NB upper front arm is mounted slightly further back. The NB spindle steering arm is repositioned for less bump steer. The NB steering rack is mounted more securely to the subframe.

Because CV joints have enough plunge that they can accomodate the additional length of the axle.

Makes sense.

is it worth swapping out a na rear subframe to a nb, will there be a significant gain?

IIRC the NB control arms (at least the front) are alightly longer.

The extra mounting points are a bonus if you get the bracing to go with them.

I just put NB front upper/lower control arms on my NA to accommodate the NB spindles/brakes 30min ago, no issue whatsoever. I did go to a spherical rod end link setup I had laying around from an b13 Se-r project due to the differences in sway bar mounting tabs. I dont really agree that the NA end link tabs are superior due to the thickness of the NB tab but thats me. I know that the NB engine subframe has better steering geometry; I would ask would I need to update to the NB steering rack if I installed the front NB subframe...

quote from keith at flyin miata: "The NA and NB control arms are the same, geometrically speaking. The only difference is the sway bar mounting point. In fact, if you buy an NA replacement control arm you'll get an NB part. The changes in caster came from the control arm mounting point on the subframe, so you'll get them if you install an NB subframe.
The steering arm on the uprights was moved up by 7mm on the NB, IIRC. The rear uprights have 5mm more track per side. The rear subframe is the same other than exhaust and brace mounting points."

So the general consensus is to go with an NB2 rear end if you have a choice? I'm going to pick up a spare rear subframe as mine is pretty much rusted through and POR15 the bitch, I guess I'll hunt down the 01+ if it has additional bracing attachment.