1 2
bigbrainonbrad
bigbrainonbrad New Reader
4/18/09 10:32 p.m.

My $500 dollar miata while being completly adequate transportation and reasonably fun has serious rot issues. I've cut out the rear quarter and had a patch welded in, but in the process of changing the tranny and diff fluids have spotted lots of surface rust. I see in the next few years that this car will most likely return to the earth from which it came.

So my thought is too make it into a locost. But in the limited research I've done, it seems like all of the miata based kits include many pieces like control arms that seem not to be in the spirit of "locost". Are there any commercially available frames or plans that make use of miata suspension pieces only? I realize that tubular control arms and stuff like that are cool, but to keep it locost, they don't seem necessary. Basically is there a kit/frame that you unbolt the miata body from and attach the locost frame?

wherethefmi
wherethefmi HalfDork
4/18/09 10:35 p.m.

Westfield has one though I believe it only uses the rear subframe. On the front suspension a macphearson strut setup won't work. Now I hope the miata has that in the front. But a locost is going to be a lot lower to the groung to the front suspensions geometry will be all borked. So enough talking out my fanny. Kierh where you at?

wherethefmi
wherethefmi HalfDork
4/18/09 10:36 p.m.

Locostusa.com is the best place for info on locosts by the way.

Salanis
Salanis SuperDork
4/18/09 10:37 p.m.

Miatas don't have MacPhearsons. They use double A-arms at both ends.

Appleseed
Appleseed Reader
4/19/09 12:42 a.m.

Keith Tanner is your new best friend.

wherethefmi
wherethefmi HalfDork
4/19/09 3:05 a.m.

See I knew I was talking out my butt

Keith
Keith SuperDork
4/19/09 10:29 a.m.

Hi!

First answer: no. There are no kits that let you simply bolt the front and rear subframes to a "Locost" chassis. If you're really looking for the spirit of small-l locost, design and build your own. Mark Rivera is doing that right now, although he's making a car with a body. Here's a PDF of the Miata subframes if you want to get an idea of what's involved.

Now, if you're talking big-L Locost, as in a Lotus Seven replica, the front suspension isn't going to work. A Locost chassis is much narrower and the engine is much further back. The chassis rails are basically shrink-wrapped around the engine. Trying to use even the stock control arms will be difficult as they're much shorter than those found in Locosts and their friends.

How much further back is the engine? Well, here's the driveshaft for my Seven compared to that for a stock Miata. The wheelbase on the Seven is actually longer.

The rear suspension is a different matter. It's mounted on a nice subframe that drops into a Locost chassis without a huge amount of work. Mark Rivera did that on his car and it's been done a number of times since. I think there used to be a commercially available kit that used it.

"The spirit of locost" is, of course, what you decide it will be. For some of us, it's a Caterham for less or a home-built giant killer. For others, it's the cheapest possible sports car. Accept that when you're looking at options, and don't tell people their "spirit of locost" doesn't match yours.

www.cheapsportscar.com if you want to get a peek at what might be involved.

stuart in mn
stuart in mn Dork
4/19/09 10:52 a.m.

There's a big difference between surface rust on the undercarriage and returning to the earth. Some preventive maintenance now may increase its lifespan as a stock Miata.

nderwater
nderwater New Reader
4/19/09 1:15 p.m.

What I don't understand is why no one sells a tube frame chassis and fiberglass body to sit on top of this:

I seems like a no-brainer to me.

dyintorace
dyintorace Dork
4/19/09 1:22 p.m.
nderwater wrote: What I don't understand is why no one sells a tube frame chassis and fiberglass body to sit on top of this: I seems like a no-brainer to me.

I agree and would think that such a 'kit' would be a big seller. You're taking a great handling set up and removing a bunch of weight. Not to mention you could then turbo the motor to boot!

kreb
kreb Dork
4/19/09 2:33 p.m.

You're right, but the Locost can offer both lighter weight and better weight distribution - the engine moved further back. Personally, If I was going to go through the trouble of building a kit, I'd want that particular advantage.

dyintorace
dyintorace Dork
4/19/09 2:57 p.m.
kreb wrote: You're right, but the Locost can offer both lighter weight and better weight distribution - the engine moved further back. Personally, If I was going to go through the trouble of building a kit, I'd want that particular advantage.

Very good points. But for those of us who lack reasonable fab skills, it might be an easier route if you could use the Miata set up as is. And, at the risk of angering Locost enthusiasts, I've never been in love with the looks of a Locost.

Keith
Keith SuperDork
4/19/09 5:01 p.m.

Check this out - I put this link in my previous post, but it might have been lost. Mark River is doing just that.

http://rivera.fotomojo.us/g/2ndbuild

There's an MG Tx replica in NZ that uses a fair bit of the Miata underneath.

There's also the Kokopelli, a swollen Lotus 11-style car that is exactly as proposed - a Miata stuffed into a tube frame with a different body. The engine is pushed back some, so either the wheelbase is extended by close to a foot or the power plant frame and driveshaft get swapped.

http://www.kokopelliauto.com/koko34.html

The problem with putting a different full body on a Miata is that then styling gets into it. Like it or not, the Lotus 7 is a tried-and-true look that's fairly easy and inexpensive to duplicate.

If you don't have fab skills, then you're looking at kits no matter what. And there are Locost and other Lotus 7-style kits such as the Westfield that bolt together without requiring much in the way of fab skills.

wherethefmi
wherethefmi HalfDork
4/19/09 5:11 p.m.

hey keith I know you have the FM ties, but between the caterham and the westfield what's the major difference, besides powerplant choices?

bigbrainonbrad
bigbrainonbrad New Reader
4/19/09 6:23 p.m.

In response to the comment about preventative maintenance on the rust, I scraped away as much as I could with a wire brush and covered that area with some leftover oil as that was what I had. Everytime I peeled back undercoating there was more rust staring back at me. I don't think that the car will fall apart while I'm driving down the road, but I realize that fighting rust is a loosing battle, I'll do what I can inexpensively, but dumping hundreds into rust prevention/replacement isn't logical to me.

Keith, thanks a lot for the links and explanation, that ability to use the rear end and all its components can help to cut down the cost. On the subject of "locost" no offense was intended or implied with my comments, I just personally view "locost" as reusing as many existing components to reduce cost.

Sultan
Sultan New Reader
4/19/09 7:13 p.m.

Keith, Do you know more about Mark River's build? For example is it going to have a full body and will it be for sale? That is a cool project!

Keith
Keith SuperDork
4/19/09 9:56 p.m.

bigbrain, no offense taken. It's just that to some people, a "Locost" is a very specific car, built to a set of plans or a slight variation thereof. To others, it's a generic term for a homebuilt.

I've been lucky to spend a fair bit of time on Westfields and Caterhams. Never built a Cat, but I've pored over them enough. And they're like jewels. Instead of simply bunging a big 1" tube in to make sure the front suspension area is stiff enough, they build a spider cage of round tubes in this fairly critical area. The interiors are full of bespoke parts and the whole car looks expensive.

As well it should, because Caterham kits are about twice as expensive as Westfields. In fact, I figure you can get a built turn-key Westfield from FM for about the same price as the equivalent kit from Caterham - all you need to add will be the powertrain and a couple of hundred hours.

Ignoring price, the choice of components is an important one. I'll concentrate on the Miata-based Westfield because that's the one I know and I think it's the one best suited to the US. Why? Because it uses parts that are easily available in the US. The wheel bolt pattern used by Caterhams is from the original Cortina (I think) that donated the spindles, and it's one you're not going to find on this side of the pond. Brake rotors, pads, clutches, transmission output seals - all the little things it takes to keep a car on the road over the years. For the Miata Westfield, they're probably in stock at NAPA. Non-Miata Westfields like the Megabusa have a similar problem.

There's also one major difference in the specification of the cars as well - IRS. The Caterham uses either a live axle or a DeDion rear, with a big wishbone serving as a non-parallel four-link setup. The bushing on this bar leads a very stressful life. Meanwhile, the Westfield has an independent rear suspension setup. According to Peter Egan and some other Caterham owners, the steering in the Miata kit is better as well.

I love Caterhams. I'd have an R500 in my garage if I could. But I think the Westfield makes an excellent car that's a good middle ground between the super-cheap Locost kits that require a huge amount of extra work, and the high cost of a Caterham.

Sultan, I'll ask Mark to chime in here and let him explain. I believe it will be for sale.

fiat22turbo
fiat22turbo SuperDork
4/20/09 9:25 a.m.
nderwater wrote: What I don't understand is why no one sells a tube frame chassis and fiberglass body to sit on top of this: I seems like a no-brainer to me.

Now where have I seen something like that before?

Oh yeah:

Colin Chapman was a smart man....

Woody
Woody Dork
4/20/09 9:53 a.m.
nderwater wrote: What I don't understand is why no one sells a tube frame chassis and fiberglass body to sit on top of this: I seems like a no-brainer to me.

I seem to recall a "new" Ginetta a few years ago that used Miata donors.

Keith
Keith SuperDork
4/20/09 10:54 a.m.

fiat22turbo, there's a big difference between those chassis designs. The Miata doesn't have a backbone - the girder you see is simply to join the transmission and the differential. It doesn't support the suspension at all. You can rock that rear subframe back and forth on the diff bushings and there are no shock towers.

It's a pretty good setup, makes the drivetrain rigid without putting the load through the unibody and eases production. It also cuts down on NVH because you can suspend the entire drivetrain without worrying about balancing deflection and isolation on things like the rear transmission mount. Honestly, I don't know why it isn't more common.

There is a Ginetta that uses a Miata donor, I forget how much of it is used. I don't think it uses the subframes but I'm not 100% sure.

fiat22turbo
fiat22turbo SuperDork
4/20/09 11:44 a.m.

Keith,

I know, I was trying to point out the obvious similarities between the two and perhaps to spark some evil ideas in others that are looking at this thread, thanks for being more than a little pedantic

Sigh, I guess I should have been more descriptive in my post. Sorry if I confused anyone.

Seriously, "finishing" the "frame" that Mazda started and fitting it under an S1 Elan (albeit with much wider body work) would be pretty cool for the person who wants the old school styling with the reliability of the modern. Although a more swoopy Lotus eleven body work would be more interesting, IMHO.

Hasbro
Hasbro HalfDork
4/20/09 11:54 a.m.
Keith wrote: There is a Ginetta that uses a Miata donor, I forget how much of it is used. I don't think it uses the subframes but I'm not 100% sure.

The Ginetta G20 just uses the Miata drivetrain in the US. I don't think any of the suspension is used. It's a blast to drive.

Ian F
Ian F Reader
4/20/09 12:25 p.m.
nderwater wrote: What I don't understand is why no one sells a tube frame chassis and fiberglass body to sit on top of this: I seems like a no-brainer to me.

I look at this and wonder how I could graft it to the underside of my crusty 1800ES... Wheel bases are only a few inches different...

Keith
Keith SuperDork
4/20/09 12:45 p.m.
fiat22turbo wrote: Seriously, "finishing" the "frame" that Mazda started and fitting it under an S1 Elan (albeit with much wider body work) would be pretty cool for the person who wants the old school styling with the reliability of the modern. Although a more swoopy Lotus eleven body work would be more interesting, IMHO.

FYI, the Power Plant Frame (the girder between the transmission and diff) is fairly soft in twist. Something to keep in mind when making mental plans...

We're seeing the Miata drivetrain getting stuffed into all sorts of cars. A Morgan owner just called up, and there's a Nash Metropolitan underway as well. Even a land speed record model T.

kreb
kreb Dork
4/20/09 1:06 p.m.
I look at this and wonder how I could graft it to the underside of my crusty 1800ES... Wheel bases are only a few inches different...

Funny you say that. I was thinking of doing the same thing with a 544. The Volvo weighs about the same as the Miata (!!) but the fenders would have to be widened....

1 2
Our Preferred Partners
wbieHYBOm7qQ1RgYMoc9ORHcEP7h2pi3jCO6iXKJ4a8JjQOvw5G8SoUEuyxUVUv8