Originally Posted by EniLab

Yes. Drag coef.
Coupe: 0.35
Roadster: 0.38

Torsion coefficient (Nm/deg) shows the torque required to twist a body through an angle of one degree. The higher amount of torque is needed to twist a body for one degree, the stiffer the body is.

E.g. Torsion coeficient of Z4 M Roadster is 14,500Nm/deg (while Z4 M Coupe's is 32,000Nm/deg).



Consider a car with a weak chasis (with low torsion coefficient) which is easy to flex and twist under force.
If using stiff springs and dampers, the shock caused by road irregularities will be transferred to the chassis directly. The weak chassis will be twisted and bent, thus the suspension geometry will be reshaped, creating non-neutral steer and other side effects that is not the original suspension design intended to cope with. Therefore a weak chassis must ride on softer springs and dampers.

For the benefit of handling stiff springs and dampers are needed. So therefore we need a rigid chassis which could cope with the stiff suspensions without flex or twist.

So stiffer chasis allows stiffer suspensions, and stiffer suspensions offer better handling.