[Trevor Booth]

Torsional rigidity (TR) is not correctly expressed as a function of the weight of the car. There are just to many factors to be considerd ie 2 seat open car, single seat, front engined, rear engined, 2 door , 4 door, the list goes on. You can compare like for like but you need to compare bare chassis weights Vs TR. A higher TR for same weight is an indication of the effective use of the material. On a tubular frame chassis the placement of tubes can make a significant difference. Bonding or close rivetting of sheet panels onto a tube frame can be of enormous benefit. In a replica tube frame GT40 7000Nm would be about the right number. But I have have tested 600kg (total)cars with a TR of 4900Nm. Reputable manufacturers of rear engined Mono tubs will apply a correction factor if tested without engine etc. A car with a high TR will handle better, can run softer springs for the same result but it is more sensitive to spring rate change. The addition of a roll bar/cage can reduce the TR as it may change the effective centre of rotation causing a higher strain energy in critical parts. If you are concerned about the TR of your chassis ask the manufacturer for the test report.