Timothy Riggs
Timothy Riggs
6/15/23 2:42 p.m.

Hello,

For years I have been highly interested in designing and building sports cars, and I have one design I want to make into reality; but I am completely new to the whole car building thing, and have many questions and concerns.

 

For context, the car I want to build is heavily inspired by the Mini Marcos - in that it's a FWD sports coupe built with running gear from a small hatchback (in the case of my car, it'd be Honda Fit running gear, rather than that from a Classic Mini). My plan is for the body to be a fiberglass monocoque body shell, just like the Marcos, but I do not really know much on designing such a thing. I wanted to ask anyone with experience with composites what this kind of design process is like, and how feasible it is.

 

And if it helps to figure out the whole thing, the car will be a fair bit smaller than the Honda Fit overall, and have a shorter wheelbase.

 

Any and all information on working with fiberglass for structures will be highly appreciated.

 

Thank you!

TurnerX19
TurnerX19 UberDork
6/16/23 7:19 p.m.

Cool questions, and I have a short reading list for you, as well as experience repairing the failures of an original Lotus Elite (type14).  A great deal of how not to do it came from the Lotus Elite, and you need to read all of its history as well as Sports and Racing Car Chassis Design by Costin and Phipps. It is available online now, someone has scanned it, but also available in print, and worth having.  There have since then been several better fiberglass monocoque chassis produced. Look at the Clan Crusader in particular, rear engined entirely Hillman Imp mechanically. Also equally successful, and structurally a far more difficult task than your idea or the Imp/Crusader is the Rochdale Olympic. Front engine, rear wheel drive, usually with a heavy iron lump of BMC 4 cylinder crudity. Resolving the torque load across the cars length adds a lot. Study both of those. Unless you can finance volume production I would build a sheet aluminum structure with epoxy and rivets. Absolutely onboard with the Fit bits!

Timo Riggs
Timo Riggs New Reader
6/22/23 3:10 p.m.

In reply to TurnerX19 :

Thank you for the info! I am taking a look at Costin and Phipps's book, and looking into the cars you mentioned.

And as far as production would go, the car would be sold as a kit car (like the Mini Marcos and Midas it is inspired by), and the customer would use a donor car. And the body shell would also be designed to accept aftermarket parts made for GE8 Honda Fits, such as suspension components, brakes, among other things to make the car highly-customizable.

TurnerX19
TurnerX19 UberDork
6/22/23 4:31 p.m.

Working carefully you should be able to amortize tooling for a room temperature cured polyester resin structure at around 30 units. The Lotus patent "bobbin" described in Lotus Elite and Elan literature is available to purchase now off the shelf, although I do not know how many per day could be had for production. Certainly a similar piece can be created bespoke, but buy the cheap stuff and build the special parts. 

Timo Riggs
Timo Riggs New Reader
6/22/23 4:57 p.m.

In reply to TurnerX19 :

Yeah, I'm sure once a handful of prototypes are built, tested, and refined the tooling will be amortized. And I already know the car will be sold in really small numbers, at least in the short run; as I know the car, even by kit sports car standards, is extremely niche. But, I'm sure sales could pick up slightly if it ends up with favorable reception, and of course I would also intend to race it wherever it can be raced.

I also thought of to do like what Fields is doing, by selling fully-assembled racing versions of the car, and the kits would be the street cars.

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