04 G35 coupe, lowered on Tein Flex Z coilovers. wheel specs front 18x9.5 offset 22 and rear 18x10.5 12 offset. should I go 245/40/18f and 265/40/18 or 255/40/18 and 275/40/18. Or do 35 ratio over 40?

test fit of the front

 

since the oem tire diameter is about 26.7" or so. I would recommend staying close to that diameter unless you have a reason to go smaller; for clearance or final drive gearing, etc...

Keeping oem diameter:
245/45R18 = 26.7"
275/40R18 = 26.7

If you want to go smaller:
245/40R18 = 25.7"
275/35R18 = 25.6"

the aspect ratio of the tire is the sidewall height labeled as a percentage of the tire section width.
245mm width x 40% aspect ratio = 98mm sidewall height
275mm width x 35% aspect ratio = 96.25mm sidewall height


if you want to do a 255 up front, matching it with a 285 is best.

if you truly want to do a 245/40R18 up front and a 265/40R18 in the rear, it'' be 2.3% taller in the rear. its do-able if you want this setup. it'll give a raked look.

 

Yea I see your point, my stock wheels are 225/45/18 front and 245/45/18 rear. I will probably have to roll my fenders in the rear to run 275/40 since the rear wheels are 18x10.5 +12 offset. I am on Tein Flex Z coils so I can play with the drop a bit if needed. 245/40 front and 275/40 rear should look meaty. thanks for the reply