I am very much an amateur and not a structural engineer but I can read and look up stuff on the web. There is lots of stuff out there but to find the useable stuff that is headache free can be quite hard. Anyway here are my homespun ideas.
A couple of the more useful and understandable items.
https://www.buildyourownracecar.com Or go to “Car basics and build tips” and then drop down menu to “Chassis”
From 2min.25s
From the above you can see that the lightest stiffest chassis is the box monocoque construction. The best space frame design is the one made up from tubes in triangles with either round tubes or rectangular section. The rectangular tube is much easier to join and to fit body panels and brackets to.
The GT40 space frame is a tricky one. Seen from the side without a roll cage it is like a convertible and is a U or channel shape, which is not good. Fitting a roll cage will help as it closes the box. However due to the door tops being part of the roof there is only a narrow section joining the front rail to the bulkhead rail. In most roll cages this effectively a rectangle (oddly shaped), which is not a stiff structure. This should be panelled top and bottom to make it into a box. Nothing much can be done about the front arms of the roll cage, which must follow the periphery of the screen apart from making the tubes out of high grade steel. There is the issue that Frank Catt has pointed out that the part of the roll cage at the top of the screen is a brain damage hazard unless wearing a helmet. A possible way round this is to make this section of tube tightly fitted to the roof and formed into a wedge shape by deforming the round tube and cover this with closed cell foam so the head will skid off it.
The rest of the chassis can be triangulated in the normal way by fitting diagonal tubes across any rectangles.
The F – R stiffness of the GT40 mono chassis is provided in a large part by the sill structure which are rib -stiffened boxes. On a GT40 space frame these sill structures are not boxed in so much stiffness is lost. On cars like the Lotus Elan the F-R stiffness is provided by a central spine which is good for handling but very poor for a side impact! The pic shows a partly built upgraded Gilbern Invader chassis I built a long time ago which has a stiff triangulated central spine linking front to rear for F to R suspension loads and engine/box to fixed differential. For safety it also had side impact frames. The roll cage is not yet fitted. The tubes were quite thin gauge and the whole chassis weighed 235 pounds.
On the GT40 space frame there is no room for a big central spine and this tube often carries pipes for cooling water etc, The best area for stiffness enhancement after roll cage and general triangulation is to look at ways of turning the sills into box structures whilst keeping a reasonable fuel tank capacity possibly by replacing the side frames with boxes.
To test your theories build a balsa wood frame and test it for stiffness by clamping one end and resting the other end on a pivot and applying twist by hanging weights on a bar.
Over to you….
Cheers
Mike