Hi currently I have a g37 sedan on Tein Coilovers sitting from about 2.5 -4 inches off the ground. With stock rims

I have purchased Ambit re02 :

18x9.5 - +22
18x10.5 - +22

I was thinking of going for 255's in the front and 285's in the back but can't figure out the ratio of height to width. How does 35 sound?

Am also currently tucking with maybe a little fender gap on my stock rims.

 

Those wheels are WAY aggressive for a sedan, even on a coupe they're a tight fit. No way will you be able to run anything wider than a 255 in back. If there's any way you can stop the wheel order and pick a set that will fit better I'd do it.

 

I have the wheels already, and only reason I thought they would fit is when I was reading the aggressive offset thread. That people fit 285s in the rear with 19's

 

It's that offset, if the offset was +40 you could run 285s but a +22 won't without fender & camber help.

 

Do you think that 275's might fit? or will I have issues also?

 

If you want to run 255s in front, order a pair of them and mount one on your back wheel first & do a test fit, that way you'll know firsthand if you have any room to go wider. I had 295s on my 10 +45 and they had no extra room, a 275 is only 10mm inside from that so you'd still have 10mm to go.
Unless you want to use more camber to get them in the fender I think a 255 is what you need back there.

 

Test fit rims .bolt them on with no tires.lower slowly onto plywood.do one front one rear.only way you will kno what will fit.post pics if u do it.