LocostUSA.com

I just found your forum and I hope I might be able to use it as a resource in my long term effort to design a light weight two seat mid engine roadster.

The main idea being an adapted FWD engine in a steel sub-frame attached to a E-glass monocoque tub with a steel front sub frame carrying the front suspension. Add a little fiberglass bodywork and it will be a full bodied road car with no top and no doors.

The target weight I've had in my mind is 1,400 lbs which probably seems quite piggish by locost standards. I was hoping that by the time my design is almost ready I can find one of the 1.4l eco-boost motors with a twin clutch manumatic that Ford will be putting in small cars pretty soon. It should give good mileage as well as good performance and the manumatic could lend itself to a racy paddle shifter setup.

It's hard to start with an engine that I can't even see, so I'll investigate front suspensions first.

I want donor parts that look nice and are not too overbuilt. With a light car that may be a challenge. The front end will be light with most of the weight in the back. My wheel choice will be as small as possible to reduce unsprung weight, same with the brakes, at 1,400 lbs or less almost any brakes would be overkill because almost every road car weighs lots more than 1,400 lbs.

My first thought was MR2 or MR-Spyder as a donor but when I looked it seems like very normal looking steel arms, nothing sexy about it. Then I looked at Miata, I think it got a nice looking aluminum A-arm setup for 2006 and newer. That's more like it but a front engine Miata has a lot more weight over the front, those arms might be vast overkill. Unless I find a better donor (must be common, probably not any Kei car stuff), I will probably design with Miata arms in mind.



So, I don't know much about Miata parts interchange but I know that Miatas started out really light in 1989 and have gotten heavier as the years went on. One web site seemed to think that the 2006 style spindle was an FWD design taken from the parts bin. So what can interchange, what is lightest and what is bulletproof? Could 2006 arms on 1989 spindles be a good light weight setup?

Thanks for the help.

Considering the size of your project, making a set of wishbones from tubing will be one of the more straightforward and easy parts. No need to look for OEM parts there. That will also let you have more freedom in other ways that may be a help or convenience in your design.

Maybe build a Locost first, which is a substantial project, before you take on a huge project like starting completely from scratch with relatively novel methods.

One thing I've found painful when working with FRP is that it is hard to do as a one person project. When it comes to big layups it's a big help to have 2 or 3 people.

While your advise of building a Locost first is sensible, I used to work at a fabrication shop and have made motorcycle powered space frame race cars in the past (but never owned one). Before that I made a carbon monocoque race car in school. My skill set is big enough to bite off what I have in mind.

As far as fabricated arms go, I agree, they would be lighter and plenty strong, even adjustable. I just like the idea of parts store and even junk yard spares. The engineering is already done and they're designed with NVH in mind. I'll climb a little to get in the car but I don't want it to drive like an all-out race car. With ~proper suspension geometry, light weight, good rubber and maybe a little down force it should handle better than anything else on the road.

You are right about layups, they can get messy and large sheets of resin saturated cloth can be a pain to lay in place single handed. I will have to cross that bridge when I come to it.

One thing I learned with carbon fiber is that if you don't have experience with how strong the result will be, you will build with major overkill which wastes money and increases weight a little. Instead of risking that I'll take a little extra weight and use much less expensive E-glass which has about 1/3 the tensile strength but won't be such a gross example of overkill when done. I can also use an old racer trick: add some black jell coat to the resin and tell people it's carbon.

The most difficult thing for me will be working out the suspension geometry and maybe some packaging but only because I haven't done them before. Which is what brings me here, some Locost builders are familiar with Miata front suspension and some may know of something better.

Sounds good. I don't crawl under and over current cars so others I'm sure will pipe up with some advice on that stuff.

One nice thing about glass is the materials are available in such wide variety. The BiAxial and TriAxial materials cut down on the work, are economical and make stiff laminates. A lot of the stuff I see in Carbon is just made from the woven cloth, I don't think it would generate good numbers for strength and stiffness. People never used glass cloths of that type for structure applications.

Have fun and send us pictures! We have a couple of monocoque builds in process, you might want to look at them and see how they connect there tubs to their sub frames... Good luck.

The miata control arms use a larger cross section and thinner metal than a fabricated arm. It would be difficult to make them any lighter.