Help - GT40 Space Frame Drawings and Plans


Hi Metin.

Two good books to read to help you understand Chasiss geometry etc.are
Competition Car Suspension Design Construction Tuning, by ALLEN STANIFORTH....Haynes books
There are many things to concider when deciding on your suspension mounts, but a good starting point would be to have
your bottom wishbone mounts parralell to the ground
your top wishbones, 2 thirds the lenght of the bottom ones, and angled down towards the chasiss at an angle of 15 degrees...your rear top wishbones would want to be at a slightly steeper angle
your rear radius rods, would want to be parralell, to the ground when your suspension is halfway compressed
This is just a rough guide, no doubt someone will say its wrong......but you really need to read these books, and make your own decisions
I hope this helps

Dear Mick

Thank you very much for your advice. I'll try to find that books. Anyway I'll do a drawing and post. Your critique will be very helpfull.


Hi Joey

How can I open your file by Solidworks ? I renamed it as xxx.sldprt and also xxx.sldasm but I couldn't open.

Hi again folks, at risk of reposting sizes that may have been put up before, here are basic dimensions of the real GT40...

Basic Dimensions

Wheelbase: 95 in. (2413mm)
Track, front and rear: 55in. (1397mm)
Length: 168 in. (4265mm)
Width: 70 in. (1778mm)
Height: 40.5 in. (1028.7mm)

Miscellaneous Heights
•Base of windscreen: 28.25 in. (717mm)
•Top of windscreen: 39.2 in. (970.3mm)
•Top of steering wheel: 31.35 in. (796.3mm)
•Minimum ground clearance: 4 in. (101.6mm)

hi joey
how can i open file?

Ian Clark

Just on a glance, the chassis has about ninety cut and mitered tubes, not counting the front and rear subframes. For the home builder, don't underestimate the amount of time it takes to cut and fit the individual tubes prior to welding. My hat's off to those who've done it. Looks like quite a project. Cheers
Hi Integrator,

What torsional rigidity figures are you getting i.e. nm per degree of twist?
Looking at the stress movie some cross bracing would stiffen things up a lot, its pretty clear where the squares are deforming.


I didn't pay attention to the torque that I applied. But you also don't pay attention to this. You can see that where's strong , where's weak. This will give you main idea. My idea: some parts of is this chassis is unnecessary strong. A chain will be broken from the most weak bangle you know. You do very very strong middle, but front and back sides are weak. This has no meaning. I prefer uniform deformation all over the body. But don't forget this is only a simple analysis. Still some parameters are abesnt. I.e. if you mount engine, it will also support the back side. Also skin parts will give more rigidity.
Get the main idea. It is all.
Someone, made the comment , that the chassis looked like a Tornado chassis, and yes it is similar, so if it is made from the same size, and gauge of material, then its torsonal rigidity, would be similar...

Metin, can you tell us about the materials you will make the chassis from...

What size...

What gauge....

What material....ERW...SHS (A36)...etc

when do you hope to start building the chassis ??



Mick, I am not very professional to build a chassis but I'm good designer and engineer. Also these works need money you know. Now these are my training studies and I'm not planning to build this chassis. May be 2-3 years later I can start. But my budget will be limited. Also in our country to find some parts are impossible. So I have to do all parts ( fiber parts, glasses, doors ) by myself. I'll use a cheap car as donor. I.e. brakes, steering system etc. I'll take from a Honda Civic or Toyota Corolla.

But if I build a GT40 I'll use a 2.0 lilter 4 cylinder 200-250 hp honda engine and place it transverserly to the rear. And my aim will be to build a car 600 - 650kg. This will be the most economic way. But I'm not sure this is possible or not. I am at the beginning of the study. I wonder that is this possible to build this chassis by aluminium.

But 10 days later I'll do a better CAD 3d drawing, and start to a 1/4 or 1/6 model of this chassis by wooden material. This will be a good experience. If I finish this CAD study I'll completely share the project by all family. My idea, if someone wants to build a GT40, at first do a model will be very helpfull.

All friends comments are important for me.
Just on a glance, the chassis has about ninety cut and mitered tubes, not counting the front and rear subframes. For the home builder, don't underestimate the amount of time it takes to cut and fit the individual tubes prior to welding.
Personally I have a cut-off saw[1] for that (well for other things but it can be used for that) but even so there are some very complicated mitres going on there which wouldn't be a single cut. I've pretty much given up on making my own space frame and I'm still wondering if its worth the time spent on anything else against say ordering the basic Tornado package and modifying it, I wonder if Andy would do just a frame and bodywork package less the suspension?


[1] Very similar to Ryobi ECO-2335 14" Cut Off Saw 110v - Ryobi available at Toolbox
Essentially a 14inch angle grinder on a spring mounted pivot above a table with a quick release clamp and the ability to angle material. Makes very short work of cutting any tubing.

" I wonder that is this possible to build this chassis by aluminium."

Thats what im doing...ive just started making the side sponsons ive been researching the project for about 1 yr. I studied the Lola T70 the Maclaren M8FF, and and the MKIV honycomb chassis

It wll be riveted and bonded, and made from 16swg alluminium

when I have the main tub finished, i will post some pics on here, but it will be a few months before i have anything to show


"It wll be riveted and bonded, and made from 16swg alluminium" . Very interesting. Cannot you find a sample photo from internet from any project. You have experience. Do u have any data about the weights of a GT40. I.e. Chassis , engine, transmission, brake system, steering system. Fiber glass parts, glasses etc.
Stiffness-wise, aluminum has no advantage over steel in a (heavy-walled) tube frame. It's quite amazing! Almost all structural metals have very close numbers: divide the Tensile Modulus by the density and you end up with about 25GPa/gm/cc. So, if you go for a lighter chassis with aluminum (and maintain the original strength), you lose chassis stiffness.

There is some advantage with sheet metal because the thicker sections of aluminum resist buckling better.

The bottom line: Steel's easier fabrication probably makes for a better tube chassis.
I completly agree with what you are saying about stiffness

When I did my reseasrch, I found this site, it has some very usefull information

Metilurgical Definitions

Here is a short piece from the site

The amount the beam or tubing will bend is NOT determined by its strength! For steel, mild steel with 40,000 psi strength and quenched 4130 with 250,000 psi will bend or defect the same amount! That assumes the same size beam or tube, the same wall thickness etc. It is a property of steel called Modulus of Elasticity and all steel is essentially the same! It also assumes the beam or tube does not exceed the elastic limit, i.e. the beam will return to its original position when the load is removed, it will not be loaded to the yield strength . A higher strength steel will bend more than mild steel before that happens.
Then why do some folks say 4130 tube is stiffer. The structure can be "stiffer" if for example a tube is made larger. Since it is stronger it can also be made thinner but then it will bend more! There are equations that can predict “stiffness” or how much a given design will bend. For example the “stiffness” will increase by the tube diameter cubed (D3)so a little increase in diameter goes a long way in increasing this parameter.
Here are some examples for steel tubes of how "stiffness" can be increased or weight reduced for the same "stiffness":
·A 3 inch diameter steel tube with an 0.062 wall is 18% “stiffer” or deflect 18% less than a 2.5 inch diameter tube with a 0.093 wall thickness and is 7% lighter per foot.
·A 2.25 inch diameter tube with an 0.062 wall thickness is about the same stiffness and weights 10% less per foot than the 2 inch 0.093 wall tube.
·A 2.5 inch diameter tube with an 0.062 wall thickness is about the same stiffness and weights 27% less per foot than the 2 inch 0.125 wall tube.

Therefore a normalized 4130 tube may be useful since it is about twice as strong as mild steel and therefore it should be capable of handling the higher stress imposed on a thinner wall tube. But be careful and don't go so thin that local bucking is encountered!
How about using other materials to make a "stiffer" structure. The following table provides a comparison of steel with some other materials based on mild steel bending a distance l for a given weight W:
MaterialFor a Load W, X= ?MaterialFor a Load W, X= ?Mild SteellTitanium2 x lNormalized 4130 lCarbon Fiber0.9 x lHeat Treated 4130lAlumina Ceramic0.6 x lAluminum3 x lDiamond0.1 x l
Note aluminum and titanium bend considerable more than steel! Of interest their “stiffness” as measured by the Modulus of Elasticity of aluminum and titanium is about the opposite of their weight compared to steel therefore the stiffness to weight ratio is about equal for all three!

As you say Bob, its quite amazing how structual matals have very close numbers


There are quite a lot of pics to be found on this site, just look through the pic gallery, it may take a long time, but you will find lots of pics
If you do a google search on the chassis I have mentioned you will find some intresting sites. Also do a search on Lotus Cosworth 25, and 49.
Just keep serching the internet. there is lots of information to be found