Few questions:

1. What's the stock fsport tire size? 225/40R18 front, 255/35R18 rear?
2. Is the AWD fsport coming in staggered because the differential/transmission has been tweaked since 2nd gen, or is it simply because the above tire sizes have a 0.06" diameter difference?

Thanks!

 

rear wheel is a little larger in the staggered f sport set up...

 

Yes, that's what staggered means.......rear wheels are wider.

I'm questioning strictly from a tire size POV, whether the 3IS is able to run staggered due to a tweak in the differential and transmission since the 2nd gen to accept staggered setups or is it simply because the stock tire size has minimal rolling diameter difference (-0.06" which is roughly -1.5mm)

 

because the rolling difference, same if you change wheels to larger size I believe it is 25" and as long as you are within in a certain percentage of that you can run those tires.... I could be wrong about the 25. but both front and rear need to be near the same just like the stock...

Design is for the staggered wheels, nothing else there is not a tweak in the Diff...

 

reyoasian, I think your second point is right. When the dealer was installing snow tires, they opted to install 225/40R18 all around instead. The rolling diameter difference, like you say, is very small.

 

Here is a handy comparison tool from tire rack

http://tire-size-conversion.com/tire-size-comparison/