Torsional Stiffness

[EgoFG]

When a car is released there is often a claim of say 15% greater 'torsional stiffness'.
The press often uses this expression or 'torsional rigidity'

Noticeably at time the FG release reviews the press said the VE had greater torsional stiffness.

What I would like to know is, since it is quoted in % gains it must be measurable - not just based on the driver impression.

Does anyone know of a source of data for 'torsional Stiffness' or 'rigidity'.
Some kind of competitive comparison.

thanks