I just got my 8 last week, and now I need to get winter tires. I've actually bought some 17" rims and already have some snow tires for them, but the offset on the rims is 40mm. Is this ok to use on an RX-8? From searching this forum, I've seen people saying 35 is fine, others saying that anything less than 45 won't work. I verified that the wheels fit over the calipers front and rear, so that's not a concern.

By the way, the wheels are 7" wide if it makes any difference. I also may use these wheels in the summer with some wider tires. So will 245s on a 40mm offset wheel fit? Thanks!

Those rims will be fine for winter tires, I however don't know why you would run 17" on the street during the summer. I also can't answer the 245 on 17 X 7 question.

http://www.1010tires.com/WheelOffsetCalculator.asp