[ViO]

I know the M8 Convertible has the “Carbon Core” as part of its door sil logo… I’m not sure if the M850 has the same “Carbon Core” structure? If it doesn’t then I believe that would be the answer (or part of) to your question. 😊

And If it does… Then perhaps the rear wheel steering assembly of the M850 weighs more than not having it on the M8?

And of course it could be any combination of the two. 😊