Rear subframe brace - NA

[Earlybird]

I'm currently in the process of stiffening up the chassis on my 91 NA and have the lower front control arm brace sorted and am strongly considering the FM stlye frame rails but the brace which I am most confused about getting is the rear subframe brace.

I am tossing up between the 2 point factory style brace ($55) which bolts onto the rear control arms and the 4 point Flyin Miata rear brace ($141 excluding postage from USA) which looks substantially stronger.

For normal street use is the extra expense of the FM brace worth it or am I better off saving a bit of coin to put to something else by just going with the 2 point brace?

The FM brace does look the goods though.....

[Steampunk]

The OEM NA8 brace is nothing more than a tube with squashed ends, not much engineering went on in designing it, but feedback from NA6 owners who've retrofitted standards ones say it makes a substantial difference, so smart inference is that a beefier brace makes a bigger improvement.
It is probably worth the extra expense as some NA8 & NB owners have fitted that brace plate (whatever you call it) that is fitted to the camber (I think) adjustment bolts, with the exhaust running through it, and they've reported THAT made a noticeable difference too.

You can't really go overboard with off-the-shelf chassis stiffening.

[Earlybird]

Just to clarify, these are the 2 types I am looking at. My car has nothing at the rear at the moment.

[NitroDann]

What are the goals specifically?

Dann

[Earlybird]

I won't be doing any track work, just want to tighten the body up.

[NitroDann]

Ok, in that case just have someone weld on a 4 way brace to the subframe and save a lot of money. Dont expect to make any appreciable difference at all with bolt on braces.

Dann

[LuckyCat]

Ok, in that case just have someone weld on a 4 way brace to the subframe and save a lot of money. Dont expect to make any appreciable difference at all with bolt on braces.

Dann

Dann, could you advise why please?

chris

[NitroDann]

Its like the hardtop and rollbar argument, some people claim a huge difference, others, nothing.

90% of aftermarket bolt ons have weak mounts, for example the hammered flat ends and holes larger than the mounting bolts.

Braces made of light guage material need to be straight and secured solidly.

Also how is one side of the subframe going to help stop the other side flexing when it is flexing the same way at the same time?

Dann

[LuckyCat]

So what you are saying is that any body bracing involving bolt-ons is a waste of time due to the method of construction?

And that a welded brace is better but there is really no benefit to either solution as all reports on these enhancements are subjective impressions?

For arguments sake, do you have any bracing regimes for your car?

cheers
Chris

[NitroDann]

My last car had a couple, that I swore were great but when I took them off over the weekend I forgot and monday I didnt realize until I checked the oil a week later.

What I'm saying is that there is no empirical evidence that there are any aftermarket braces that make an difference to actual stiffness.

Things like the hardtop dampen vibrations and move when the 100kph shimmy happens by a few KPH, from say 103 to 105 or 106 however this doesn't prove that the hardtop stiffens the car, infact anyone looking at the hardtop mounts can see clearly that no stiffness is added, the damned thing is sitting on soft rubbers all the way around.

On top of this, a LOT of aftermarket braces are designed very poorly, usually mounting to extremely flimsy parts of the car like the firewall or being flimsy themselves, having bends, no triangulation, small bolts/hardware etc.

If you brace the car, choose a brace that is designed with solid engineering principles, and put it in a place where removing a tiny amount of flex will improve actual performance improvements, don't just be happy that the natural frequencies of the cars flexing vibrations have changed slightly.

Dann

[LuckyCat]

Dann, so really, no one can provide actual evidence that chassis bracing is beneficial: a placebo if you like.

Therefore the standard strut bar where fitted is also useless (for example the NC) because of its design (4 points and physically not a strong design ). Yet Mazda fit it to the car - for looks?

Under what circumstances does does a car chassis flex? They must be far beyond what an average driver is going to achieve. and where is chassis bracing going to be beneficial? Only on the track! I suspect and in some circumstances if may be more advantageous for the chassis TO flex.

So chassis bracing in it self only provides security. After all the main benefit of the MX5 in performance situations is its PPF. Doesn't need anything else for the real driver?

cheers
Chris

[Lokiel]

Consider the Beatrush PPF brace instead:



http://www.good-win-racing.com/Mazda-Performance-Part/61-0554.html

[Earlybird]

Consider the Beatrush PPF brace instead

I would if my car had the factory tabs welded on. Mine is early 91 which had NO factory fittings for a brace (see pic below).

I have however found another option to throw in the mix but haven't found any reviews on it. It does look to be a copy of the racing beat brace though, only cheaper.
http://www.ebay.com.au/itm/Rear-Chassis-Brace-89-97-MAZDA-MIATA-MX5-/160502740315#ht_5709wt_922

[sailaholic]

A proper bolted connection works on clamping force not shear force on the bolt.

There is nothing wrong with bolted connection for bracing if it's tieing together two hard points. The shape of the brace also makes no difference if it is loaded in pure tension or almost no difference in pure compression assuming the member is stiff enough to resist buckling loads

Stiffness of the brace in said conditions is directly related to the material stiffness.

So the best brace material will be the one with the highest stiffness per unit weight.

This means a steel brace of the same stiffness might actually be lighter.


And finally......
NEVER look at the pricing of something from fm as plus shipping when evaluating. Their post is stupid expensive.

Sent from my GT-I9100 using Tapatalk 2

[Earlybird]

Ok guys, with respect to all those who have responded I am no closer to deciding on a brace but can clearly see there's 2 sides to the fence .

Those who own or have owned an early NA with no bracing and then fitted something please feel free to offer your real life findings.