NA6 / NA8 front swaybar geometry and effect of NA8 fitted to NA6 vehicle

[twr7cx]

According to US Miata parts sellers, Flyin' Miata and Racing Beat the NA6 from 1989 to 1993 front swaybar geometry is different to the later model vehicles:

Note that the geometry of the 1990-93 and 1994-05 bars are different.

As such they offer NA6 specific front swaybar products.

But Australian swaybar suppliers, such as Whiteline and Pedders, list the same front swaybar part for all NA models (both NA6 and NA8). Anyone know if what they are selling is the NA6 or NA8 setup? What is the effect of NA8 front swaybar geometry fitted to an NA6?

[Zed]

I believe the earlier (earliest? ~1989??) had thinner bars and customer-feedback asked for less body roll
around ~'93/4 when the 1.8 was introduced there was another option of thicker rear (the bilstein suspension equipped cars?)

although this is from previous years 'google-fu' not personal experience

also down to drivers preference (car lean or slide?)

Rich.

[Aiming Faster]

The End Link mounting face is one difference, with an adjustable End Link the extra twist can be easily accommodated.
Whiteline and Pedders both supply adjustable End Links.

[manga_blue]

NA6 were supplied with 19/12mm bars and 164/97 lb/in springs
NA8 were supplied with 19/11mm bars and 154/97 lb/in springs

End result of those charges were that the NA8 was very slightly more softly sprung and had an almost imperceptibly greater bias towards understeer.

[twr7cx]

I believe the earlier (earliest? ~1989??) had thinner bars and customer-feedback asked for less body roll
around ~'93/4 when the 1.8 was introduced there was another option of thicker rear (the bilstein suspension equipped cars?)

NA6 were supplied with 19/12mm bars and 164/97 lb/in springs
NA8 were supplied with 19/11mm bars and 154/97 lb/in springs

Thanks Rich and manga_blue, but I'm not referring to the thickness of the swaybars themselves, those differences are well documented, but rather their different geometry that Keith from Flyin' Miata mentions which also has an effect on their operation.

In regards to my question on fitting an NA8 front swaybar to an NA6 I found https://forum.miata.net/vb/showthread.php?t=615835 which details that some minor modification was required due to clearance issues.

So there's more too it. The NA8 and onwards swaybars are mounted differently due to the longer 1.8 motor and as such have longer sides to reach to where they should.

I'd imagine that the Whiteline and Pedders offerings are actually NA8 and onwards units as that's the bigger market.

[manga_blue]

I believe NA6 and NA8 have the same geometry. Hence Whiteline offer only one set for 89-97. The end geometry on the NB8A is distinctly different.

I have used the Whiteline adjustable set on my NA8 using the original end-links. It took some "fine tuning" with a vice and a sledge hammer to set the end links to fit but they worked perfectly after that. Sorry I can't comment on them on an NA6 but I've heard it's the same situation. The end links need a little persuasion then it's all good.

I still have that a set of Whiteline adjustables in the shed. V little use. Interested?

[twr7cx]

I believe NA6 and NA8 have the same geometry. Hence Whiteline offer only one set for 89-97. The end geometry on the NB8A is distinctly different.

I'd be surprised that Keith Tanner from Flyin' Miata, that only specialises in Miata's (MX-5's in the USA), and Racing Beat, that specialise in only Mazda performance parts, have both independently identified that NA6 and NA8 swaybar setups are different but are actually incorrect and Whiteline with their range for a wide variety of brands and models got it right... Perhaps if that is the case then ADM NA6 MX-5's received

I have used the Whiteline adjustable set on my NA8 using the original end-links. It took some "fine tuning" with a vice and a sledge hammer to set the end links to fit but they worked perfectly after that. Sorry I can't comment on them on an NA6 but I've heard it's the same situation. The end links need a little persuasion then it's all good.

Perhaps then Whiteline have created there's somewhere between the NA6 and NA8 spec in an attempt to fit both but the end result is they're not perfect for either?

I still have that a set of Whiteline adjustables in the shed. V little use. Interested?

Yes, I just want to make sure that they're going to work though... Why do you not use them any more?

[plohl]

I have put na6 bars in an na8.
With adjustable end links you'll be fine, regardless of bar. You'll have more issues if you you're running stupid low, or have silly high spring rates and big thick bars.


What's the intended purpose of the car? I lean towards using the springs for most the balance, and the sways for just tuning depending on track and conditions.
If it's a road car, and your running springs close to standard rates, a bigger NA bar will be fine, though I tend to steer clear of the 16mm rear bars.

Just remember - the front adjustable white line bar - used to have 3 holes, I think they dropped it down to 2, because you couldn't put it on the softest setting.

[manga_blue]

Yes, I just want to make sure that they're going to work though... Why do you not use them any more?

There were never any technical problems with the Whitelines.

At that stage the car was 90% track and 10% road. Heavy bars front and rear give an impressive feeling of flatness and control on public roads but these don't translate into better track lap times. Better lap times were the only thing I was chasing, so I went from 5/4 Kg/mm springs and Whitelines to 10/7 springs with no bars at all. That format took most of the NSW club class lap records but was unstable under brakes in the heavier braking sections. Adding OEM 22/11 mm bars restored braking stability (it used to duck and weave) without hurting lap times.

Basically if you want to race then use stiff springs and add minimal sway bars just to fine tune under/oversteer balance. An NA doesn't have enough torsional rigidity to make use of both heavy springs and heavy sways without a lot of stiffening. If it's road use then just go with somewhere between standard rate and twice standard rate springs so you don't break your teeth and flatten it out with heavier sways.

Currently the car is a fun car around my local coast and mountain B-grade blacktop roads. It's back on 5/4 springs with only the front 22 mm bar. That gives me a reasonable compromise between ride, roll stiffness and grip. We have so many bumpy, patched, corrugated roads here. Smaller bars and lightweight wheels let the tyres move freely and independently over the bumps to maximise grip.

[RS2000]

Good posts by plohl & manga
I'm one of the many that bought larger swaybars, then had to ditch the 16mm rear bar.
Also, I found that reinforcing, or using stiffening blocks, on the flimsy OE front arb mounting brackets, has the same effect as going to a larger bar.

[twr7cx]

Thanks for the replies.

I have put na6 bars in an na8.
With adjustable end links you'll be fine, regardless of bar.

From the discussion on Miatanet forum it seems that it's the reverse - NA8 bars on NA6 that seems to be the issue - although I would have thought the issue would be both ways. Perhaps it's actually a LHD/RHD issue?

You'll have more issues if you you're running stupid low, or have silly high spring rates and big thick bars.

Standard ride height on the original 89 NA6 springs so maybe a bit of sag... Currently standard sway bars.

What's the intended purpose of the car? I lean towards using the springs for most the balance, and the sways for just tuning depending on track and conditions.
If it's a road car, and your running springs close to standard rates, a bigger NA bar will be fine

It's a road registered special interest vehicle - so limited to 104 drives a year on public road. My wife and I both drive 4WD's as our daily vehicles so this is the 'fun' car that we share when were not needing to transport the kids etc. We live semi-rurally so there's a minimum of 500m of dirt track to leave home and then country (rough) backroads.
It's currently on (what I believe to be the original) NA6 springs with new base level KYB shocks, Flyin'Miata improved bump stops front and rear and Flyin'Miata NA rear shock top hats for extended shock travel - this setup combined with the factory NB 15" wheels (as I found performance tyre options to be non-existent in factory 14" sizes - running RE003's on the 15" - I've stuck with OEM wheels as they're cheap and not too bad in weight) is comfortable and absorbs the bumps well on these roads. Were I find it letting down is on spirited corners - there's a huge amount of body roll (and this is coming from someone who daily drives a 4WD with 3" lift and 33" tyres so is used to body roll as the norm), a feeling of reaching the limits and some rubbing sounds. I suppose I'm wondering if there's a way to find a balance between retaining the current comfortable ride quality that we currently have for these rougher roads whilst increasing corner performance to deal with some of the above mentioned - to do so am I better off with
1. firmer springs and appropriate shock absorbers (perhaps an entry level brand name set of coilovers?) to suit while retaining the current OEM swaybar combination, or
2. retaining the current spring and shock combination with aftermarket thicker (stiffer) swaybars.
I'm having difficulty understanding which option would have a better effect on the corner performance with the lesser effect on ride quality.
Reading both your post and magna_blue's it would seem that the pair of you in general recommend stiffer springs and softer swaybars?

On a less important note, PDA do track days and skid pan days locally which I'd like to go and have a play with - but this would just be for fun so I'm not looking to tailor the suspension towards this side activity...

though I tend to steer clear of the 16mm rear bars.

Is that not required to balance the car back out if the front swaybar size has been increased? Not sure if I have it corretly, but on a RWD vehicle doesn't increasing the front swaybar result in understeer?


I look forward to your thoughts and comments.

[RS2000]

Yes increasing the front bar size increases understeer or reduces oversteer, but do the maths on the bar area (not diameter) increases:

Going from a 19mm to a 24mm front bar is an area increase of 59.6%
Going from a 12mm to 16mm rear is an area increase of 77.8%
If you have an 11mm rear, the area increase to a 16mm is a staggering 112%

I have an article from Supermiata / 949 Racing where they say they have yet to find a NA or NB that needs more than a 14mm rear.

[twr7cx]

Going from a 12mm to 16mm rear is an area increase of 77.8%
If you have an 11mm rear, the area increase to a 16mm is a staggering 112%

I have an article from Supermiata / 949 Racing where they say they have yet to find a NA or NB that needs more than a 14mm rear.

Great point there and explanation, thank you. I notice that Whiteline only offer a 24mm front swaybar and 16mm rear. Pedders and SuperPro both offer the same (which is no surprise as I believe that they all have shared manufacturing arrangements in place now). Is there a local (Australian) suppliers/options that offer more appropriate rear size, such as 14mm, or is it international import required then?

The only thing of note is that Pedders do offer a 22mm (BMF12) front swaybar option as well as the 24mm option.

[RS2000]

Signature sway bars (Selby) in Nowra NSW make quality custom adjustable bars in any size you want.
In 2017, I paid $535 for a set delivered - 24mm front, 14mm rear, both 3 point adjustable for an NB8A. I notice Whiteline is almost this price now for the NB8A set.

https://www.facebook.com/Signature-Swaybars-360126180698377/

[plohl]

Mazda did design the mx5 to be rolly... and the trye noise isn't a huge issue… just get a few odd looks…
Anyway, first thing I would check is your tyre pressures. I found on strictly closed, private mountain roads, that my old NA6 would handle fine with average tyres on the 14" wheels - provided I had the tyres pressures at what was recommended on the door card. Around 28psi I think. I would say between 28 and 30 psi a good place to start - less and tyres make more noise, more isn't necessary for a standard car on public roads.

I would lean towards a set of decent coilovers if you have the budget - the key here is getting the spring rates right though - most of the shelf stuff will come with 8 and 6kg/mm springs or stiffer. A set of MCAs (blues or whatever the street stuff is called these) and get whatever springs you wanted.
I would probably lean towards 6 and 3, or 7 and 4 kg/mm (front and rear). Both set ups with standard sway bars.
6 and 3 will give you let you "push" a little more, with a balance close to standard NA8, where 7 and 4 will not only be a little firmer, but a bit pointier – the rear will want to rotate a bit more. Manga's set up would also be good, and I agree that the software bars help on uneven surfaces.

For reference, I went from 9kg/mm front springs, to 11.5kg/mm and dropped the sway bar from 24mm, to the standard 19mm and it was noticeably less darty on bumpy roads and racetracks, and more comfortable overall (though I wouldn’t say my car is comfortable compared to a standard car).

Cheaper option is to buy some king springs from their race catalogue and use them with your standard shocks – you’ll nee to get the spring ID right so they match the standard shocks. They spec rates in in/lb though, so you would be looking at 300 and 150, or 450 and 250 (might bet a little too stiff).

If cash is tight, just start with a stiffer front bar and some adjustable end links. Either a signature or whiteline 24mm, or see if you can pick up an NB 22mm bar for cheap. Leave the rear bar alone.
The 16mm bar is “meant” to balance the front bar, but I’m not quite sure an overall analysis of the car was done to get to this size. I know some of the old 2F race cars used soft springs and big sway bars to get the balance they wanted, but I’m not sure if this was a solution for the times, or if the 1 or 2 fast guys were doing this, so it must be a better set up.
Ultimately, having both bars would make your car more planted around the corners, and if you’re driving with too much spirt, you’ll likely be happy with it. If you were to take it to the track, or skid pan, you would find it wouldn’t be very forgiving at limit of grip (tend towards oversteer). The idea of getting signature to make you a 14mm bar is also a good one.

As always, it’ll come down to money.
I lean towards –
1. MCA coilovers with softish springs. I would go MCA because built locally, lots of spring options, good product.
2. King Race springs with the rates above on the standard shocks. Not the OTS king springs for the mx5. I have no idea what rate they are.
3. Bigger front bar – 24mm or 22mm - adjustable endlinks get 949 ones, they're good applies to any sway bar change... and ever handy on standard bars.
4. Bigger front bar 24mm and bigger rear bar 14mm
5. Bigger front bar 24mm and stupid big rear bar 16mm