So I just picked up 4 18 × 8.5 g-spiders. I've got an AWD fairly low on some BC coils. I plan on running spacers to fill my wheel wells out. My question is simple: what is the best tire size for me to run?

 

mine was on g spider before rwd-if you're running 8,5 all the way might suggest do 225x40 in front,it will stretch a little and 255x40 plus 20mm spacer (hub centric) to make a little wide and out,or you can go with 255x35 which has a minimal speed reading difference, just to look your ride more lowered plus easing a little of your negative camber,

 

fyi, 255/40-18 is a full 1" taller than 225/40-18. not sure if the 2is awd system will like that. food for thought.

i'd recommend 225/40-18 all-around.