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.

I have decided its only worth swapping any sub-frame (with Steering Rack included) to a NA only if its broken, its just too many hrs of intense labor, welding and 22 bushings.

More details.

Front: the lower control arm mounting points are moved for a bit more caster. The NB steering rack has a stronger mounting. I'm not 100% sure on brace modification points. I would recommend going to the NB spindles, which also means you want the NB upper control arm due to a change in the ball joint. NB arms also have more reinforcements as well as that modified sway bar end link mounting point.

Rear: The subframe geometry is identical. The mounting points for the braces changed, but are the same for all NBs - you can attach the stronger 01+ Sport braces to the 1999-00 subframe, although you'll find you're missing one of the twin bolt holes on the tub. Exhaust hangers were moved. The uprights have 5mm more track on each side. Again, the control arms are dimensionally the same but have some extra reinforcements.

No welding is involved to swap them around - my 1994 Targa car has a set of 2005 subframes on it. It also has an NB exhaust so the exhaust hanger changes aren't a problem.

I think the best bang for the buck is the front subframe due to the better pickup points.

He (OP) has both of them.

That is wrong the rear suspension geometries are Identical. the difference in 5mm track width differance is because the stock wheels went from 45mm offset on the NA to 40mm offset on the NB.

If you followed the armchair engeneers on Miata.net from the mid to late 90’s this should have caused the rear wheel bearing to explode by running anything other than the stock 45mm wheel offset.

Bob

Bob. the track increase came from the wheels and a change in geometry in the rear. Check the specs and you'll see the NB rear track increased more than the front. You can also check the factory 1999 Service Highlights book - that's where the 5mm number comes from.

However, the statement that it's from the subframe is incorrect. It's the hub carrier that changed.

So the extra 5mm in the rear came from the Hub carrier? What is the hub carrier? Spindle, lower or upper arms? I just put 01+ rear hubs/spindles with 95 axles and it appears the axle doesnt seat completed in hub, a few mm off?

NVM-it is what the hub is pressed into. Do you think it's safe to run the 95 axles with 01+ hubs being that the surface of the large part of the axles don't seat fully against the hub carrier?

Track widths f/r

NA 55.5/56.2
NB 55.7/56.7

So 5mm difference per side is in the wheels. That would mean the NB suspension geometry is ~2.5mm narrower per side in the front and ~1.35mm per side wider in the rear.

So the NB rear upright puts the wheel 1.35mm further out I guess. That is like negligible in my opinon. I almost wonder if it is round off error and a units conversion by the marketing folks.

The change in front geometry and rack mounting is a bit more significant however.

Bob

From the 1999 Service Highlights book.

So that make it a total of 10mm difference in width in the rear? I wonder how this is going to make my car drive...

Ok so in reality the rear track on an NB is 20mm wider than an NA, 10mm for wheels and another 10mm for the knuckles, and the marketing people in the brochure call it 1/2"

Bob

It will handle the same as it would if you were to add 5mm spacers to your old setup. The rear geometry of the NB with stock wheels is the same as a NA with 10mm wheel spacers on its stock wheels. and the 5mm you get from the uprights won't make much difference that it would be very noticable.

It wouldn’t surprise me it the real reason mazda widened it wasn’t to go after improved handling. I would about bet it was because the Clay model guys in styling got into adding more clay and then when they were real happy with the shape of the fender they found the wheel looked too far inboard compared to the fender so the styling guys petetioned to have the wheels pushed it out not the handleing guys.

I will also say running less offset on the wheels doesn’t screw up the handling of the car at all in the case of the Miata. I think my car handles and feels better than it ever did now with now 20mm spacers behind 15X9 949 wheels. I don’t think I’ve gotten to the point of diminishing returns yet, wider is better.

Bob

for a street / autox car this seems counter intuitive. Wouldn't you want less caster for quicker steering?

Well, the NB cars are quicker in autocross aren't they? So I guess it worked :)

Any idea as to whether the MSM uprights are the same as the other NBs?

I believe the hubs are different but the uprights are the same. Remember, the MSM has fatter axles so there need to be changes to accommodate that. No geometry changes of which I am aware.

I am digging the idea of picking up a nb front subrfame. Thanks for all the info guys!

So the NB axles are 5mm longer then the NA axles I am getting mixed reviews and I see lots of part stores list the same p/n. Im talking a late NA not the early 1.6.

Wow, are we still having this conversation?

The axles are the same size for all 1.8 cars except the MSM. The early 1.8 NAs (94-95ish) originally used two-piece axles, but they are all dimensionally compatible.

The part numbers varied during the original production run as the design of the CV joints was tweaked several times, but as service parts, Mazda lists the same unit (MD-25-500) for all non-turbo, ABS-equipped 1.8 cars in the Collision Guide:

https://www.miataturbo.net/attachmen...ine=1312567410 https://www.miataturbo.net/attachmen...ine=1312567410

Awesome thanks the info I was looking for.