[brandallson]

As a brand new member, this is my first post. Please be charitable if I inadvertently demolish some of the conventions established in this forum. Anyway. . . .
Last February I departed with my beloved 2007 328i when I bought a 2016 435i Xdrive coupe. Obviously, I am loving every mile I drive! However, the tire situation leaves me very confused. As implies, I purchased the car used with 25K miles. The tires/wheels that came with are 225/40/19 Goodyear RFT (square configuration).
To begin, I am confused with the size of these tires/wheels as I have not been able to find any factory configuration that has 19" tires squared. I see a lot of 18" squared, and 18/19 staggered, but not 19" squared. Is this a factory configuration. What the hell did I buy?!?!?! Moving along.
Early last winter I bought a set of studded Hakkapeliitta 8's for my 328i. WOW! I stuck to the snow and ice like velcro! Hands down, the best winter tire I have ever met (btw, I spent half of my life in Alaska; I have seen a few studded tires over the years. The Hak-8's are truly, "otherworldly").
My main question: I I still have the Hak-8's and am curious if (1)--I would be committing a sin against BMW if I installed them on my 435i-x. How far can we safely push minus sizing? (2) Is the mere notion of putting 205/55/16's on my 435 insane? To be sure, I expect that this would result in a noticeable reduction in performance/handling -- but it is winter, after all. Even a speed fool like myself won't be rounding corners at 90 mph in the ice and snow. Important side bar: I have great floor jacks, impact wrenches, and a large garage. I intend to swap the studded tires out with all season Michellan Pilot Sports as weather conditions change over the course of the winter.
Does anyone have helpful advice? Heck, even your unhelpful advice and general mockery would be welcomed.
Thanks!
Brett