The calculations have been done and it is as we suspected. The torsional rigidity of the chassis is, not to put too fine a point on it, crap.
Right, how to stiffen things up?
The body, contrary to what I always thought, does add significantly to the torsional rigidity of the chassis, so this is where I plan to attack the problem. I have dropped the idea of widening the central section of the chassis as this just makes more problems.
My plan is to stiffen up the floor
A and the box section
B covering the chassis with carbon fibre. I will glue the carbon fibre panels that surround the door opening
D to the existing body and join the floor carbon fibre to them. I will also triangulate the joints between B-D.
I will then bolt the body to the chassis with a lot more fasteners than the standard 16, especially in the cental box area. I will sandwich the body between the chassis flange and a steel strip in order to add axtra stiffness.
The roll bar fits to the body fasterners 13 and 14 and bolts to the chassis at the locations in red
C
I will also look to add vertical stiffening between the body's central box section and the outer body panels wherever possible.
All extra weight, I know, but sometimes there is no choice :-(