Originally Posted by Steved
Some of you will already know my car (Z4M Coupe) that was featured in EVO magazine last year. The problem does not lie in the Z4M's chassis, the body rigidity of the Coupe is more than the E92 335i.
My car was substantially improved by two things; firstly the Z4M comes fitted with Series 1 Continental SportContacts, these are horrible tyres some 4-5 years out of date and no longer on sale. The current version of these tyres is the SportContact3 (i.e. 2 versions on). BMW fitted these to the Z4M because at the time Continental could not supply the SportContact2s for such a small volume of cars. In other words BMW compromised. I and subsequently many other owners have changed these to Pilot Sport 2s (on 19" CSL rims) and the grip and steering response is considerably better.
The second improvement, which was again very obvious to anyone that has driven a Z4, was to fit the standard BMW strut brace across the strut towers. This comes straight out of BMW's parts catalog for the Z4 and instantly allows the front and rear end to feel balanced when loaded up in a corner. Without this the front struts move under cornering creating a dislocated feel between front and rear axles and causing the rear end to snap away into oversteer.
Two very basic improvements (that BMW should have made themselves) that I am quite sure would have reversed the comparison with the 335i. Other track tests even between standard 335i and Z4MC have borne this out, so the results in C&D are a combination of the particular track plus the poor configuration in which BMW provide the Z4M.
I suspect that the primary advantage the 335 has vis a vis the Z4M is weight distribution.