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I don't think there was much (any ?) support in the floor of the 7 in that area and have no idea about the Ginetta. For me I think it will be parallel trailing arms and a panhard rod. Simple except for the panhard rod attachment.

I too have a '69 Sprite that I would like to turn into a modified Locost. I also have a sufficient pile of 1" dia .049 wall 304 stainless tubing that I snatched up years before Locost emerged with the idea of building a "replica Birdcage".
I would probably go with Spitfire uprights and maybe drop back to a 948cc BMC "A" motor in the spirit of the early 7's, but even with a stock 1275cc I wouldn't think the engine is what's going to break the frame. The narrow rear axle looks like a challenge and I suppose I could use a Morris Minor rear.
Can any of you CAD FEA guys please comment on the merits of 1" x .049 SS vs 1" square mild steel?

The original Series 1 Lotus 7 had a frame that was only 39" wide. it used a Nash back axle that is 47.25" wide. Tha Midget/Sprite axle is the same axle with just smaller drums.
The book frame is therefore 3" wider than the Lotus frame. It was said that Colin Chapman designed the cars around his own dimensions. He was 5' 9" tall, and I'm guessing 150-175 lbs. It's all about that" adding lightness".
I too am about to start to build a 7 replica. I'm using George Cushings drawings as my blueprint. Look up JDs build log. He is using MGB uprights and brakes. The MGB and Sprite use similar uprights. For a lightweight, small hp car they are suitable, especially if your want the earlier look. I am using MGB uprights, fabricated A arms, and a Sprite back axle. I am aiming for a total weight of 800-900 lbs. I am using a Suzuki G10 engine and a Samurai 5-speed. It amazed me that I could pick the engine up complete, and walk across the garage with it no sweat. I'm also into Hot Rods, my coupe having a 283 SBC, so I'm not used to all this lightness!
The Vintage race guys have to use the Sprite back axles in their cars, as they came with them! You can buy stronger axles from Winners Circle. Generally, the only time they break axles is when they get off track and on to the grass, the revs go up, and then they get back on track the tyres grip and the axles break. That back axle lived fine behind that engine and trans. The 7 is going to end up only 2/3 the weight of a Sprite. The same applies to the uprights.
My advise is use everything out of the Sprite. Then again, I'm 5' 10", 165 lbs!

Is that SS round? !" round is %20 lighter then square tubing. Your tube is also 1 size thinner. You could look up the weights on onlinemetals.com and then get some idea how much more stress it would be under. I think you can do it, but it raises the bar a bit on welding quality and understanding how the frame works. Start another thread when you are ready to have a go....

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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I love the idea of building a Locost from a Sprite, but I'd have to agree that .049 SS is too thin, even if you could keep the weight under 1000 lbs., which is unlikely. T304 has a lower yield strength than mild steel, and there's a fair amount of bending stress in a Locost chassis. Almost any other grade of stainless would be better.

On a standard Locost frame, the rear track needs to be at least 51" with very skinny tires, and 52" with a 185 section tire. That leaves out the Sprite axle, and even an MGB axle unless you go with really thick wheel spacers.

I've been off on a spring vaca although why one would leave the great weather we are having I don't know.

Using the Sprite rear axle is going to be a real challenge. I plan on solving part of the width problem by using the Sprite seats and getting my bum up off the floor. I am hoping this will also allow a more Sprite like WB (80"). If I use 84" I could almost stand in the front behind the axle. I have solved most of the front end suspension attachment problems and will now start on he rear. As soon as I finish I will post some sketches.

Here are some crude 3D models of my project to date. The tubes are all shown as round but I intend using mostly square, also most of the bays are not triangulated to keep the sketches simple. The dash bulkhead is not in it's final location until I get the seat buck done. Some of this design is similar to the Westlake XI mostly because that car a;so uses Sprite suspension. The front suspension is quite a challenge because it uses trunions instead of ball joints and requires the A arms to swing in parallel. To solve this problem I have canted the four upright tubes back at 5° to give me 5° of camber. No adjustment

The Sprite rear axle is also a problem as the rear track is only 44.75" Getting two bottoms and a drive shaft into that space isn't going to happen so I have rearranged the rear end so the trailing arms are offset to the inside. This results in an offset load which I hope won't be too bad. This also pushes the seats forward of the tires. I won't get this solved until I build the seat buck.

I plan on building up front and rear subframes and then the seat buck. That way I can adjust the WB a little. It is amazing the Sprite had only 80". No wonder they are easy to spin.

As I found some Triumph rubber suspension bushings for this retro build I could now use some mounting brackets, Does anyone know of a source for the "book" style brackets?

I have gotten pretty much no where finding someone who makes Locost suspension brackets and I'm not looking forward to hacking them out and then bending them in a vise. So I whipped up the attached drawing and am sending it out for quotes. I used to work with a fabricating shop so I know there are 100 better ways than hacking, bending and drilling alla Champion. As this sort of thing is much cheaper in volume I am hoping some other forum members will be interested. So please let me know.

Have you looked at Jack's parts? Sorry for the double entendre (or Am I?)

http://kineticvehicles.com/brackets.html#suspension

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

I did, his parts are designed for use with rod ends these are designed to use the Triumph rubber bushings.

Gotcha!

In that case take a few hours looking at the site for AA Mfg. http://www.aa-mfg.com/pdshop/shop/ or just order a catalog and browse thru it in an evening. I'm sure you will find something that should work, even if you have to go with 2 tabs each. Then you can define the gap. At minimum, it should give you reference pricing for your design.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Yahoo!! AA has quoted me per the print, $5 or waaay less than I could do it for. Less if I order in volume. Anyone interested ??

That was fast! According to the time stamps on the messages, that was 15 minutes. Had you already contacted AA before I mentioned them?

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

I did all my bracket fabrication with a chop saw and drill press. First I hacked up a 2x2 tube into bracket sized pieces, drilled them while the "box" was still closed, then whacked the seam side off. Considering the rest of the build, this was one of the easy parts. I used aircraft washers as spacers to fill the gaps since the inside of the bracket was a bit larger than the control arm ends.

John