The entire purpose of that IS-C middle section was to produce a convertible. That was the original intent. If we all remember the LF-C2. If I recall dealers begged for a 7 seat RX and the convertible was canned. So it had that extra weight for no reason
BMW is going to race the M4, going to be interesting to see.
I have heard it does not provide any benefit, but a rigid chassis is always better than a softer chassis even at the cost of some additional weight. There are always other ways to reduce weight. Jason C wrote about how M division was unhappy with the previous F30/F80 3-series given to them by the BMW. In order to achieve a lighter chassis, they cut a lot of corners on it. I once posted a picture of an M4 vs RCF rear subframe and you can see how much engineering Lexus put into the rear subframe, which makes it ideal for coilover setup (while the M4 suffers from rear subframe cracks if punished extensively).
In the case of the RCF, a more rigid chassis keep all four wheels more planted under very high G-loads in the turn since it would resist torsional twisting of the chassis or "jiggly" behavior when tossed around. High speed stability wise 90 mph feels like 30 mph in RCF for the same reason.
I remember reading Lexus in the press back in 2015 that the chassis was so stiff that it could be made a convertible and the roof can be chopped off without a significant reduction in torsional stiffness. The convertible never got out of concept stage.
The floor pan, inner rocker structure, rear gussetts and front apron thickness were all increased to give the monocoque even higher rigidity. A good alternative example is, race cars have roll cages that adds up to 100+ lbs of weight in the car and a lot of it is much farther away from from the CoG, but it actually helps the handling of the car when pushing it to the limits (other than safety).
I hear ya. Good points. Need to get ya to a race!
Yeah, I wish. It would be incredible to be in those cool events you go to and see a GT3. Live too far away, family, kids, career yadda yadda! My RCF is a garage queen LOL There is a new track opening up in my city so hopefully I can get out there maybe, this summer (if they open it for the non-members).