Clearance issues mainly as most 225s are going to be to tall, change the gearing a considerable amount and usually add usually add a fair amount more weight in the worst possible place to add it. A 225 will work quite well on an 8" wheel but optimal handling is almost always gained from a little stretch, why I run 9" wheels on 225 tires but I am also rather extreme in my mods.
I would stick with 205/40 or 45 or 215/40 size tires if you can find the tire tire for your need in those sizes.
Not sure what kind of tires you are looking for but from your location and the fact you have your autocross setup it would seem you need AS tires unless you want summer only and do not plan to drive in the winter or use winter tires on other wheels, etc....
From the tirerack site, a very good all season for the money, well reviewed, no 215/40 offered, BFG Comp-2 AS.
215/45/17 compared to the 225/45/17, .5" wider at the sidewall but only .2 wider tread and .3" taller and adds 2lbs per corner.
http://www.tirerack.com/tires/tires.jsp?tireMake=BFGoodrich&tireModel=g-Force+COMP-2+A%2FS