Miata frame rail reinforcement

My local metal shop is willing to make me frame rail reinforcements (hog trough for those of you that are old school) out of anything I want for relatively cheap. I was going to have some made recently, but something came up so let's say I have time to think about the material.

The old guy at the shop suggested 1/8", but I think that's a wee bit overkill... and heavy. I will be using these to support the transmission mount (think: ) and I will also be using it to connect to the front subframe and the rear subframe. My question is, how thick do you think I should go? 1/8" will work, obviously, but maybe 3/16 will work just as well and not be as heavy.

Thanks!

3/16" is 50% heavier than 1/8"...

I would find one of the popular aftermarket pieces and see what they use, though 3/32" sounds about right.

You should think about the best way to use that metal rather than just slapping more on, see where you can drill holes or link pieces to gain strength. Look at the Flyin' Miata butterfly brace, it's not a couple of "hog troughs" slapped onto the frame rails.

He's just talking about the frame rail reinforcements, not a butterfly brace, though.

I think you'll find guys like me who have paid for Flyin' Miatas development work on these won't be too keen to hand over any real details.

Not to mention, the butterfly brace is a great addition to the rails. My '90 is pretty stiff with those, frog arms and a roll bar.

lol, why I went up is beyond me. Not a morning person, which sucks because that's when my classes are.

And swank is correct. Also note, I'm not using my frame rails in the same manor they are. Similar, but still very different. I'm concerned about a few additional forces.

FlyinMiata's stuff is 14 gauge stainless, which for those of you who don't know is 5/64th. The suggestion from Duke sounds about right at 3/23". What I need to do is stop being lazy and put this all into solid works and see what I'm working with.

As a side note, V8 roadster also uses 14 gauge mild steel. Also make a note that stainless is a softer, less ridged metal than mild steel. That, and it costs more money. V8 roadster has their trans-mounts also connected to the frame rails which tells me that it is probably good enough. So either 14 gauge or 13 (3/32") gauge. I also need to decide how I'm going to tie the front and rear subframes in.

I'm using a XJ12 rear end, so I can replace the two arms that come out and tie them into a plate or something attached to the frame rails. The front, I can probably do some sort of linkage, think 4-link type arms. Cross bracing is simple enough, and don't forget jack points.

In reply to z31maniac:

They post anything important right online . The actual dimensions will be specific to my requirements, but they put the thickness and the material (as far as I care to know, I'm not making mine out of stainless)

EDIT: Also, as a note, I could probably just but their butterfly bracing and use it with my frame rails. As long as they don't get in the way of anything.

EDIT:EDIT: Maybe not, I don't think I'd be able to squeeze a trans mount in there :-(. It is good looking stuff for sure thou.

Number 1 miata chassis stiffener is doorbars

Jaynen wrote: Number 1 miata chassis stiffener is doorbars

Really? I've looked into them, but can't see taking away another 2" between the door and the tunnel.

z31maniac wrote:

Jaynen wrote: Number 1 miata chassis stiffener is doorbars

Really? I've looked into them, but can't see taking away another 2" between the door and the tunnel.

Door bars are the most effective bolt-in way of stiffening a Miata, but most aren't willing to make the sacrifice.

I somewhat doubt you'd even lose 2" with some of the offerings that are out there. Looks to be pretty unobtrusive other than slight PITA getting in and out. If you have a Hard Dog Roll bar, there's even Hard Dog door bars meant to integrate perfect with those roll bars.

I'm thinking about doing Door Bars AND the FM frame rail reinforcements on the MSM. Seems silly, but it'd be nice to have a jack point that doesn't suck. And this way i can almost break even on weight by removing my factory "butterfly brace."

Swank Force One wrote: I somewhat doubt you'd even lose 2" with some of the offerings that are out there. Looks to be pretty unobtrusive other than slight PITA getting in and out. If you have a Hard Dog Roll bar, there's even Hard Dog door bars meant to integrate perfect with those roll bars.

I've sat in a couple cars with door bars -- I hate them. Very uncomfortable because it's right up against my leg. It also massively reduces the already limited selection of aftermarket seats that will fit in a Miata.

Not to be prying, but is it just because of the way you fit? Or do you... well... "overflow" over that edge of your seat?

As mentioned, most seats are a tight fit, taking away more space seems like a bad idea.

I've already got a Hard Dog roll bar, Frog Arms, FM Rails and Butterfly brace.........are door bars going to do anything other than add weight at this point? I'd like to buy them, but I'm curious about interference with the seat.

I have a harddog roll bar, side bars are meh as far as comfort thou

z31maniac wrote: As mentioned, most seats are a tight fit, taking away more space seems like a bad idea. I've already got a Hard Dog roll bar, Frog Arms, FM Rails and Butterfly brace.........are door bars going to do anything other than add weight at this point? I'd like to buy them, but I'm curious about interference with the seat.

I'd say you're braced to the point that anything from here out would be fairly minimal gains. Money better spent elsewhere.

I've seen triangular shock tower brace for the NC miata, I wonder if they have something like that for the NB.

In reply to Baylis:

Actually, looking at the same pic I have found, it appears that IS a NB... lol

Edit: http://www.mossmiata.com/Shop/ViewProducts.aspx?PlateIndexID=112898

I don't know how useful the tie-in to the firewall is. Ever pushed on a firewall before? They ain't exactly something i'd want to mount something structural to.

Sure LOOKS purposeful though, doesn't it?

Yea, since they are coil overs, a tower to tower brace wouldn't do much. A lot of the race people seem to swear by the triangular braces, because I think everything from the towers back is "supposed" to be structural. I don't know, thought I'd throw it out there and see what people thought while we were on the topic of chassis stiffening.

A shock tower brace does make a difference to a Miata, but I'm not convinced that tying it to the ultra-thin firewall would do anything. Heck, it's not really a firewall in that area, it's more of a rain gutter.

The yellow NB in the picture is also fitted with an M45 supercharger, which means he can't fit a better shock tower brace and also speaks as to how well he evaluates his aftermarket parts Honestly, the 2001-05 factory shock tower brace is better than almost every aftermarket one out there as long as you have an NB and can fit it under the hood.

Coilovers isn't the relevant aspect. Shocks vs struts is what you meant. But the control arms are still mounted to the sides of the engine bay, which is a big open box.

Well, I put coil overs in the same respect as shocks in this scenario. I figured if you didn't have struts, there was little need to tie the towers together. But Kieth would know better than I! lol... I'll keep this in mind

If you define "coilover" as a coil-over-shock assembly, then it can mean either shocks or struts. Struts are always coil-over-shock, but shocks can be as well. As in the case of, say, a Miata.

If you define "coilover" as "a coil-over-shock assembly with an adjustable perch", then the same applies.

Sounds pedantic, but it makes for clearer communication and less confusion - especially since it's relevant to the discussion at hand, as struts vs shocks do feed their load into the car differently.

Swank Force One wrote: Not to be prying, but is it just because of the way you fit? Or do you... well... "overflow" over that edge of your seat?

While I'm not a skinny guy, I don't think that's the issue. It's more that I'm 6' tall and my legs are long enough that my left leg wants to occupy the space that the the door bar is using.

Moral of the story is, before you buy door bars and drill holes to bolt them in your car, sit in someone else's first and see if they bother you.

Ah ok so you move your knee towards the door for space. I do that with my right leg so that makes sense.