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[Koldun]

My apologies for being a total noob and if this has been asked before. I used the search feature, but didn't find what I was looking for. Maybe my search-fu is just weak.

Background info: Currently running 245/30/20 in the front and 295/25/20 in the rear. Wheels are 20x9.5 and 20x11, not sure about the offset (will know after alignment on Saturday).

Anyway, after barely over 12,000 miles, my hankook v12s need replacing in the rear (the previous owner had way too aggressive negative camber I think, the inner edge is all worn out while the outers still have easily 60% tread left). In search for replacement tires, I discovered that both the 18" and 19" stock factory rear wheels have roughly the same circumference of 26.35"/26.3" compared to the front circumference of 25.72"/25.75".

Question 1: Far be it from me to question BMW engineers, but is there a reason for this disparity in wheel circumference? Am I losing in performance/handling/anything by running a 25.81" tire in the back (the fronts match up pretty close at 25.79")? Do I stand to gain anything by changing the rears to 305/25/20's (26" circ.), or am I just introducing understeer given the disparity with the fronts?

Question 2: I don't think I can go 255 width in the front as I see many people doing, since the current 245/30s rub at 7/8 to full lock, and using the ruler method from the spacers thread, the wheel is pretty much flush with the fender. However, are there tire brands that run a little wider than the Hankooks? I've read in some threads that the Michelin PSS tires tend to run a little fatter, but I'm not sure I can justify that cost for cruising/summer wheels (have a mint set of OEM 19"s I plan to use for that, at least until I can some 18" monoblocks). Are there cheaper alternatives for a fatter tire?
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[SUBFRAMERIPPER]

12,000 seems about normal wear for rear tire replacement.