235 mm tires, great fit but not too wide
 

The May 2012 issue of Grassroots Motorsports made a convincing argument that an 18" wheel and tire does indeed go faster and is more consistent than a nearly identically sized 17" wheel and tire.

But... Road and Track showed that for our torque challenged cars, having a wider, larger diameter 18" wheel and tire package was slower than a narrower 17" wheel and tire package. See this post:

http://www.ft86club.com/forums/showt...tire+size+test

So... I played around with some calculations using the 1010tires.com website (see the attachment). It seems that the 235mm tire width is a great tire size for a wider tire fitment. Overall diameter is JUST UNDER the stock size for both 17" and 18" wheels. These fall in between the near-stock 215 or 225 tires and the I-want-them-as-wide-as-I-can-fit 245 and 255 tires. Here are the two sizes that are closest to the stock diameter:

235/40R17
Lots of tires (but certainly not all) are available in this size. A good option.

235/35R18
I have found only a few tires in this size. This is a shame, because given more options these would be my tires of choice. If you could find a really good tire in this size, the FR-S/BRZ/GT-86 should be faster with it.

ugh, tire choice and wheel choice is limited when we want 18" wheels with 5x100 and a lower offset.

If I could get a sticky modern tire in 235/35R18 (dreaming, I know) and had deep pockets (more dreaming), I think one of these wheels would work:

http://www.forgeline.com/products/on...lock/ga1r.html

http://www.forgeline.com/products/on...-open-lug.html

I think it's really cool that you could spend 1/4 the price of the car on a top-of-the-line set of wheels and tires!