I'm not getting the grip I expect under acceleration with my OEM 235/50-18's. It's probably just that they're overdue for replacement and don't have much tread, but I'm remembering that I got much more stability from my previous 5 series which had 245's in front and wider 275's in back.

I wonder if I should look into a wider tire for the back. Could a small increase (say 245) be made without changing wheels? What sizes would fit? Is this a terrible idea?

 

You could do a 255/45-18 without it negatively affecting the speedometer.

I would add this is an open differential car and if you are used to limited slip equipped cars, the open diff is extremely limiting. I don't recall driving mine hard enough for wheel slip, but I do have new Hankook Noble tires.

 

I'm running 265/35/20 on my SV8.