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

[manga_blue]

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Let's just try putting some maths around this.

Currently you have an NA6 with standard springs and sways. i.e. 2.9/1.7 Kg/mm springs and 19/12 mm sways. Front Roll Couple (FRC, google it) is a predictor of under/over steer balance. FRC for your car now is 58.9%. Around 57% is perfectly neutral handling in an NA, so yours has that very slight touch of understeer that Mazda designed. Roll stiffness (resistance to body roll) for your car is 871.8 ft lb/deg. As you already know this is quite rolypoly. It just happens that this is also very grippy.

If you just added Whiteline adjustables then, depending on which settings you used on the ends, your figures could range from:
61.5% / 1293.9 ft lb/deg with front bar on hardest, rear bar on soft, to
48.2 $ / 1408.0 ft lb/deg with front bar on softest, rear bar on hard.

That's an enormous range of adjustment and both these extremes could make the car almost undriveable. (This explains why so many people have had trouble with adjustable large bars : stupid settings)

The ideal setting would be front medium/rear soft to give 59.4% / 1285.0 ft lb/deg. That would mean you retain the soft ride you have now, the under/oversteer balance remains essentially the same but roll stiffness is increased by about 50%. SO you have a car which is still pleasant as a country tourer but feels lot flatter.

I wouldn't stress too much about whether the Whitelines fit your car or not. Whiteline have been selling this set for NAs for 20 years. If there was a fitting problem it would have rectified by now.

I might just reiterate my general advice about springs and sways. Stiff springs, small sways = race car. Light springs, stiff springs = road car.

If you do want to consider stiffer springs as well then you will have to go back and recalculate optimal sway sizes. Springs are the major adjustment, sways are the fine tuning and you can't consider either in isolation.

[manga_blue]

Sorry about all the duplicates. The site is acting weird today.

[plohl]

I was using the spread sheet I got off you a few years ago now to come up with the springs rates The spreadsheet has been modified a little, but I've tried so many combinations now, that even if the numbers aren't exact, I can compare different set ups and have a reasonable idea on what it's going to do.

[RS2000]

If you retain the factory spring rates & go with larger sways, I would think you'd go with 22mm F & 14mm R bars.
The area increase for 19/22 & 12/14 is almost identical. That retains the factory F/R ratio, with flatter cornering. Fine adjustment could be had if bars are adjustable.

plohl, you said possibly pick up a 22mm NB front bar, but I thought front NB bars didn't fit NA's ?
The rear bars are apparently the same, so a 14mm NB rear might become available (on SE I think)

Cheers

[manga_blue]

If you retain the factory spring rates & go with larger sways, I would think you'd go with 22mm F & 14mm R bars.
The area increase for 19/22 & 12/14 is almost identical. That retains the factory F/R ratio, with flatter cornering. Fine adjustment could be had if bars are adjustable.

plohl, you said possibly pick up a 22mm NB front bar, but I thought front NB bars didn't fit NA's ?
The rear bars are apparently the same, so a 14mm NB rear might become available (on SE I think)

Cheers

22/14 would be almost perfect for an FRC of 57.6%, roll stiffness of 1117 on stock springs. Problem is the NB bars are not compatible with NAs. Not sure but I think it's more than just the end fittings. Maybe the NB arms follow a different path which fouls the control arms? Can't quite remember.

[RS2000]

The Whiteline rear bars are the same part no. for both NA & NB. The front bars are a different no. & shape.

Anyway, as I said earlier, Signature will make any size to suit any model.

[plohl]

I swear a mate has an NB bar in his NA - i'll have to look into it. I can't remember if I have one in the shed or not, else I would go put it in and see.

I find a lot of the adjustable bars a bit of a pain as you end up with the end links on stupid angles. How much difference that makes... idontknow.

I turned up some ally spacers to move the end link mounting on the rear LCA for the 14mm supermiata rear bar I have so the end link was relatively straight.

[twr7cx]

Thanks all again for the huge volume of comments and thoughts.

Not the OTS king springs for the mx5. I have no idea what rate they are.

Incase your interested, they are:

Lowered coil springs (progressive rate design used):
Front KMFL-52 ranges from 165 – 215lb/in
Rear KMRL-53 ranges from 105 - 160lb/in

Standard height coil springs:
Front KMFS-52 230lb/in
Rear KMRS-53 140lb/in

I found it interesting that the progressive rate on the front doesn't get as high as the standard fronts linear rate but the progressive rate on the rears does get higher than the standard rears linear rate.


My problem with replacing my current coil springs is I don't want to lower the vehicle at all. From what I've read the early NA6's were one of the lowest from factory. I'm happy with the ride height as it is as it already rubs on the curb of the driveway to the workshop as it is. I have a feeling that my current ride height would be somewhere between the King Spring standard and Lowered ride heights.
If changing springs then I think I would be safer with a set of coil overs allowing me to ensure that I achieve my desired ride heights.

Signature sway bars (Selby) in Nowra NSW make quality custom adjustable bars in any size you want.

MX5 Mania Motorsport are showing a Signature rear bar in stock https://mx5mania.com.au/collections/swa ... 4377014306 . There description does not however include any sizing details - I've e-mailed them to see what sizes they stock or if they get any that you choose when you order.

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.

Looks like they've actually gone down in price now - $235.00 a pop from MX5 Mania Motorsports! That's a nice change!

Roll stiffness (resistance to body roll) for your car is 871.8 ft lb/deg. As you already know this is quite rolypoly. It just happens that this is also very grippy.

...

The ideal setting would be front medium/rear soft to give 59.4% / 1285.0 ft lb/deg. That would mean you retain the soft ride you have now, the under/oversteer balance remains essentially the same but roll stiffness is increased by about 50%. SO you have a car which is still pleasant as a country tourer but feels lot flatter.

You mentioned that the roly-poly nature of the standard setup results in the vehicle also being very grippy. Does this mean that if thicker (stiffer) swaybars are used to increase the roll stiffness (resistance to body roll) that it will actually result in reduced grip? i.e. would the factory setup fo 871.8 ft/deg have more grip than the Whiteline swaybars fitted on front medium/rear soft to give 59.4% / 1285.0 ft lb/deg?

Sorry about all the duplicates. The site is acting weird today.

It's been down for me all day today.

[twr7cx]

If you retain the factory spring rates & go with larger sways, I would think you'd go with 22mm F & 14mm R bars.
The area increase for 19/22 & 12/14 is almost identical. That retains the factory F/R ratio, with flatter cornering. Fine adjustment could be had if bars are adjustable.

22/14 would be almost perfect for an FRC of 57.6%, roll stiffness of 1117 on stock springs. Problem is the NB bars are not compatible with NAs. Not sure but I think it's more than just the end fittings. Maybe the NB arms follow a different path which fouls the control arms? Can't quite remember.

Pedders offer a 22mm Heavy Duty front Swaybar - part number BMF12. Seems that it is not adjustable as their 24mm front swaybar option and 16mm rear swaybar options both specifically state Adjustable in the title.

As said though, both the 22mm and 14mm sizing should be achievable through Signature Swaybars doing a custom job.

plohl, you said possibly pick up a 22mm NB front bar, but I thought front NB bars didn't fit NA's ?
The rear bars are apparently the same, so a 14mm NB rear might become available (on SE I think)

Problem is the NB bars are not compatible with NAs. Not sure but I think it's more than just the end fittings. Maybe the NB arms follow a different path which fouls the control arms? Can't quite remember.

Yes, everything I've read, and there's a number of threads with details about it on Miata Net, indicates that the from NB bars do not fit NA's but the rear bars do.

If you just added Whiteline adjustables then, depending on which settings you used on the ends, your figures could range from:
61.5% / 1293.9 ft lb/deg with front bar on hardest, rear bar on soft, to
48.2 $ / 1408.0 ft lb/deg with front bar on softest, rear bar on hard.

Could you please educate me more on how you are calculating the difference that adjusting the swaybar position (hard, medium or soft) has?

[twr7cx]

Wow wee thanks for all the details and opinions. I've tried to read most of the posts two or three times at least to try and take it all in. Clearly there isn't really just one simple answer - it's all a bit of a balancing act as changing one thing effects others. On top of that it's all completely subjective as it's not a track car so were not measuring for faster lap times, nor are we testing for more g's on a skidpad... What one prefers for a cruiser car might not be the flavour for another.

What I'm getting from your comments though is there seems to be two contrasting schools of thought on what I could/should do:

Option 1: Fit stiffer aftermarket sway bars (seems that 22mm front and 14mm rear along with adjustable links are the highest recommended options) with factory soft springs aiming to retain factory like comfortable ride quality with the soft springs while controlling the roll through the swaybars.
Having Google'd and read about this option it's discussed on many different forums beyond just that of the MX-5/Miata world and has many fans of. Some of the concerns raised about it though are:
1. the stiffer swaybars cause one wheel incidents, such as hitting a pothole, to be transferred to the other side too resulting in a feeling like both sides have drive over a ditch.
2. soft springs don't help the vehicles pitch control under acceleration and braking where stiffer springs would - not sure that this is a concern for me as the little NA6 doesn't have huge acceleration or braking capabilities! It's certainly not an issue I've noticed while driving it.
3. I didn't really understand it but on washboard corners.

Optional 2: stiffer springs with factory swaybars. It seems that while this resolves some of the above mentioned concerns it would likely result in a harsher ride quality which is not desired.

It's hard to know what I'd prefer the most without trial and effort, but I think at the moment Option 1 is possibly the best way to go. Fairly well priced to try without significant time and effort spent. Sticking to just 22 front and 14mm rear should mean it's not too significant a change to to hopefully incur some of the concerns I've read about.


Out of interest I notice that Keith Tanner from Flyin' Miata recommends the following for the NA6 chassis:
Front springs: 318 lb/in (5.678834kg/mm)
Rear springs: 233 lb/in (4.160906kg/mm)
Front ride height: 12.5"
Rear ride height: 13"
Front swaybar diameter: 22.225mm (7/8")
Rear swaybar diameter: 15.875mm (5/8")

Front Roll Couple (FRC, google it)

I've been checking out this Tutorial at http://fatcatmotorsports.com/FRC_TUTORI ... TORIAL.htm which gives some details on it, how different setups effect it and it's effect

[manga_blue]

Out of interest I notice that Keith Tanner from Flyin' Miata recommends the following for the NA6 chassis:
Front springs: 318 lb/in (5.678834kg/mm)
Rear springs: 233 lb/in (4.160906kg/mm)
Front ride height: 12.5"
Rear ride height: 13"
Front swaybar diameter: 22.225mm (7/8")
Rear swaybar diameter: 15.875mm (5/8")

That setup would have so much oversteer it would be unroadworthy. Keith Tanner is not the guy I'd pay any attention to on suspension tuning. If you're reading Fat Cat Motorsports then you're on the right track.

My car is neutral on 5/4 Kg/mm and 19/0 mm. 5/4 is about the reasonable comfort limit for a couple on my local coast and mountain roads, which I guess are very similar to Tas roads. I know several guys whose wives won't travel with them anymore on 7/5 or 7/6.

FWIW I have dríven a couple of MX5s with progressive rate springs. I hated them. Mushy turn-in. Few, if any, benefits mid-corner from the firmer part of the curve. Mushy exit.

[twr7cx]

If you just added Whiteline adjustables then, depending on which settings you used on the ends, your figures could range from:
61.5% / 1293.9 ft lb/deg with front bar on hardest, rear bar on soft, to
48.2 $ / 1408.0 ft lb/deg with front bar on softest, rear bar on hard.

Could you please educate me more on how you are calculating the difference that adjusting the swaybar position (hard, medium or soft) has?

Hey manga_blue, any chance of telling me about how you calculate the difference in the swaybar positions?