Chassis flex in NB8A

[CoachOz]

Having had both an NB8B and an NC, I'm aware that there's a lot more chassis flex in the NB8A and it's pretty unpleasant on our rubbish road surfaces on the Mid North Coast. Hopefully it's possible to fix this, so I'd appreciate any suggestions.

[ManiacLachy]

There are lots of ways to stiffen the car up a bit.

First, the easiest, cheapest and least obtrusive is some delrin door bushings.
https://atperformance.com.au/product/na-nd-mx5-delrin-door-bushings/
http://beavismotorsport.com/store/solid-door-bush-for-mazda-mx-5-na-nb-nc-nd-89-17.html - I note these are plastic, not sure if they work as well as delrin?

From there things jump up in price! You could look at roll bars like Automotive Plus's offerings, I especially like the twin hoop for a subtle look. Brown Davis is another local option. I love the Blackbird Fabwork's GT3 Bar, but I'd hate to think about shipping it here.
http://stores.ebay.com.au/Automotive-Plus/Roll-Bars-/_i.html?_fsub=4964886018

Frame rail braces.
http://www.jassperformance.com/shop/Frame_Rails_Reinforced
https://www.flyinmiata.com/fm-frame-rail-reinforcement-kit.html

And cowl braces.
https://v8roadsters.com/product/cowl-stabilizer-braces/
https://www.flyinmiata.com/strong-arms.html

There are other braces, like at the diff, or FM's butterfly brace also available. Also a hardtop, if that's your thing, will stiffen the car nicely. I wouldn't worry about shock tower braces though, while almost all these methods of stiffening the chassis will invite some debate, shock tower braces seem to be the most universally discounted.

Most of these will have stories on various forums, or videos on YouTube to help you gauge their usefulness.

[ManiacLachy]

Oh, one other thing... Your photo in your signature is quite large, usually bigger than the message you post. Could you shrink it down a bit? It can be quite distracting

[KevGoat]

MX5+ torque box roll bar
FM Chassis rails + butterfly brace
Delrin door bushes

Shocks/springs/bumpstops in good condition and that actually work together - won't reduce flexing but can affect the way the body reacts to road surfaces.

I have an NB8C SE with twin hoop roll bar, chassis rails (no butterfly brace just the factory SE braces) and the door bushes. Each of these made noticeable improvements. I also fitted a 3 point strut brace but really these are more visual than structural.

Only butt science in my choices .....

EDIT: Lachy beat me to it lol ...

Sent from my SM-G930F using Tapatalk

[ManiacLachy]

The fact that we both said near the same thing speaks volumes though, Kev!

I've got the twin-hoop and door bushings. I'm eyeing off frame rail braces and cowl braces, but I want to spend money elsewhere first (wheels!). It helps of course that the SE is the most braced of the NA/NBs from factory.

[hks_kansei]

Focus on where the doors are, that's where it flexes most due to having less car there.

Rollbars don't actually make much difference since they're usually mounted on the parcel shelf where it's not actually that bad for flex, compared to the door openings.

To be honest, I'd just look into buying the centre bracing from an NB8B and call it done.

(Well actually I just ignore it, only time I really notice is when I angle into my driveway the interior light comes on)

[CoachOz]

Thanks for the suggestions, and the signature .

I've ordered the delrin door bushings as a first step and will look at chassis rails next.

I have a hard top and notice that it makes quite a difference, even having the roof up helps. But what's the point of having a convertible and having the roof on all the time.

[kiezon]

(Well actually I just ignore it, only time I really notice is when I angle into my driveway the interior light comes on)

Lol Jesus. I own an NB8B and don't really notice much flex now that I have delrin door bushings. I still need to send payment through for the Jass Performance frame rails. What are your opinions on frame rail bracing for the NB8B?

I also feel that the cowl/frog arms are necessary for when the car travels on a bumpy surface. It just loses all composure.

[ManiacLachy]

But what's the point of having a convertible and having the roof on all the time.

My thoughts exactly! But to each their own. Thanks for the image resize, much better.

See how you go with the door bushings and go from there. I like to do changes one by one to better feel their contribution. I certainly noticed the roll bar change.

Lokiel has the full suite of chassis stiffening mods, and somewhere he has a hierarchy of how much they helped for him, though this was from before delrin door bushings were a thing.

[CoachOz]

To be honest, I'd just look into buying the centre bracing from an NB8B and call it done.

Pardon my ignorance but what does this look like and where is it on the car?

[Lokiel]

Here's my rankings on my SE BEFORE I installed Delrin Door bushings:

I have an SE so it had the most factory bracing of any NB.

1. (by a country mile) MX5Plus Twin Hoop roll bar
I noticed the difference immediately in my car, slowly driving out of the original parking lot of MX5Plus where it was installed, I turned right and the car felt noticeably different. much stiffer.
There was a small roundabout nearby and once again, the car felt noticeably different.
NA and NBs suffer a lot from chassis twist, something that was addressed in the NC - the Twin Hoop roll bar with built-in torque box fixes this a LOT.
Some say that roll bars do nothing but for me it was immediately obvious, even at very low speeds - t suspect that the doubters have not experienced the MX5Plus roll bar with its built-in torque box.
Roll bars are a great safety item in a convertible but the NA/NB stiffening alone makes them a worthwhile investment (I consider the safety aspect just a secondary point) - good place to mount your track camera too!

2. Boss Frog Frog Arms (no longer available but FM and V8 Roadster make similar items)
Fast turns feel much sharper and cowl shake over rough/undulated surfaces is reduced a lot.

3. FM Frame Rails
These were installed before the Frog Arms and I really couldn't feel any difference at all.
I did find though that when I jacked up the car, the other wheel on the same side got airborne much earlier so it definitely stiffens the car.
They're great for jacking up the car too, jack from the centre point and change both wheels/brake pads for track day at the same time!

4. Carbing 3pt Front Strut Brace
Front Strut braces have dubious merit in MX5s.
My car had an OEM front strut brace and the Carbing brace is even stiffer.
Can't tell the difference with or without the brace - would like to drive an un-modded SE with and without the brace to see if there is any difference.
I keep the Carbing brace because it looks "schmick" and makes a nice place to lean on when working in the engine bay.

With all these mods, when sitting up on 4 jack stands, my car pivots diagonally if the jack stands aren't even - even Dann commented on it when he had my car.

Door bars are another option to eliminate chassis twist but they make entry/exit even harder so aren't really practical for anything other than a track car.

IMO, the #1 NA/NB chassis stiffening upgrade is an MX5Plus roll bar but you should also do the Delrin Door bushings too since they're so cheap.

[hks_kansei]

To be honest, I'd just look into buying the centre bracing from an NB8B and call it done.

Pardon my ignorance but what does this look like and where is it on the car?

It essentially looks like a big flat sheet of metal with holes stamped into it for access to things like exhaust and gearbox.

It mounts underneath the car, pretty much right from where your feet are to where your bum is (like an undertray)

I can't confirm if the NB8A has the correct holes/captive nuts to bolt it on easily though.

I'll try and find a pic.

[hks_kansei]

https://image.rakuten.co.jp/carus/cabin ... b470fr.jpg

It's the black brace here, NOT the red ones.

(Also apologies, I remembered incorrectly, it doesn't go the whole way down, it stops about midway. Even so, it shoudk still help)

[CoachOz]

https://image.rakuten.co.jp/carus/cabin ... b470fr.jpg

It's the black brace here, NOT the red ones.

(Also apologies, I remembered incorrectly, it doesn't go the whole way down, it stops about midway. Even so, it shoudk still help)

Thanks, I'll see if I can find one

[Mr Morlock]

delrin is plastic. Whether delrin makes a difference is probably not proven i.e. if you replace worn originals with new originals does it improve / so replacing with a hard plastic is that the right choice. Why did not the Mazda engineers use delrin ,bearing in mind that the engineers could have specified delrin in the first place. All oem parts are specced out and selected as the right choice.

I have an BB and it does not flap like an MG TC or a TR4 and it has not been modified so maybe and quite probably HKS is right. What does it matter if there is a little movement ( i.e. not so bad that a door cannot be opened). I always thought that screwing lumps of metal onto chassis rails is over the top and introduces holes and gaps where moisture can cause future corrosion . One of the great things about an MX-5 is how well it rides- supple and good roadholding for road use.

So maybe just do one thing and see what happens.