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Hi guys,

As you can guess, I am still excited with recent NB acquisition so trying to mod the car as "sensibly" as I can.

I would like your opinion on whether FM rails will be duplicating the OEM sport chassis brace I recently installed in my car. The sport brace was from a 2000 or 2001 NB off the wreckers which I transfered to my 1999 NB. The brace made such a huge difference to rigidity that I am now greedy for more rigidity.

Has anyone with a >2000 MX5 installed an FM rail, please share your experience if you have.

To be quite frank, I felt my previous NA felt more rigid compared to the NB before I installed the sports brace. I was pretty gobsmacked by the level of cowl and door rattle when I went over some corrugation. NB8A I have to say felt pretty shockingly shitty in that regard.

Hey there,
I'm looking at doing exactly the same thing, can you give a bit of detail as to what you had to do to fit the bracing? Was the chassis pre-drilled? I need to find a wrecked NB8B first! I was going to install the NB8B braces instead of going to the trouble of of a butterfly brace or frame rails........less drilling!

Frame rails do make a noticeable difference. I have an SE, then installed an MX5 Plus twin hoop rollbar, followed by FM Frame Rails, then Boss Frog "Frog Arms" and noticed the stiffening difference each time. Here is how I rate/rank them:

1. MX5 Plus twin hoop rollbar - 10/10
This has been my #1 chassis stiffening mod, I noticed how it affected the car immediately when making a right turn out of MX5 plus and I was barely moving.
NA/NBs really need more stiffening across the width to prevent chassis twisting.
If you only do one mod, the rollbar should be THE ONE.

2. Boss Frog Frog Arms - 7.5/10
Definitely stiffened the front up, I get much less rattling of the dash over corrugated surfaces (ie. minimises cowl shake) and the front end feels more communicative.

3. FM Frame Rails - 6/10
These do stiffen the car up but not as noticeable as the Frog Arms.
I installed these before the Frog Arms so it cannot be said that they made less difference because I had the Frog Arms installed.
They definitely stiffen the car up though. When I remove my main jack from under the car, I need to use the scissor jack to give me enough clearance to extract the main jack. When I do this, the only wheel that is touching the ground is the one diagonally opposite the scissor jack; the wheel on the opposite side of that one is raised substantially.

4. Racing Beat Rear chassis brace - 0/10
This was on for about 2 weeks before I removed it.
I didn't notice any difference at all, probably because of the Roll Bar.
I removed it because the the lower two bolts have an offset washer with calibration marks that fit into a receded slot that has calibration markings on it. When you add the rear chassis brace, you cannot see the alignment marks and the washer is no longer restricted to move within that receded slot as intended so you're never sure that both sides are aligned correctly.
See the right hand side for best example of this (sorry for the size, not my photo, I'm just linking to it):

Thanks for your feedback. Crap...now you have encouraged me to spend more money on getting a roll bar with a safety excuse thrown in. I have ordered the chassis rail but will get the roll bar from MX5 parts UK as it seems like a good balance between construction quality and looks. I think the landed price is around $450.

I would imagine that the SE had a hell of a lot more stiffening compared to the 1999 NBs so what would help a SE would definately help an 1999 NB with a greater margin.

Incidently, I am getting a really annoying scuttle/rattle coming from the left hand side of the car which seems to be coming from the door area. Is this common? My cowl area is as quiet and stiff as anything but the bottom left hand side scuttle is just plain annoying. Can this be due to a lack of chassis rigidity or perhaps some lose wires within the door itself?

Anyone else experience this?

samx5 wrote:Hey there,
I'm looking at doing exactly the same thing, can you give a bit of detail as to what you had to do to fit the bracing? Was the chassis pre-drilled? I need to find a wrecked NB8B first! I was going to install the NB8B braces instead of going to the trouble of of a butterfly brace or frame rails........less drilling!

MAZ wreckers in Dandenong South has plenty of written off MX5s. There is minimal drilling required to install a sports frame but the Dean from Mulgrave welded some brackets into the chassis. $150 all in all to install. The Sports brace from MAZ cost me $200.