everything is relative to how aggressive you want the fittment. with that being said...class is in session. for the most part 20/30mm are the front over fenders sizing. there is a company thatll custom make fenders up to 50mm front and 85mm rear but they are about 700 a pair and 4 week wait period. anyways...

on stock fenders you can get away with 17x9 front 17x10 rear. if you stretch the tires like 225 front tire and a 245 rear tire id say you can safely run a 17x9 +20ish 17x10 +20ish and keep your camber in check.

now if your run say a 20mm front fender and a 30mm rear (really common setup) you can +/- 0 offset all around. its still safe you might need a lil camber but not much.

IF YOU STEP UP TO 50MM REARS you better have some super dope balla rims. 50s are what the OG bitchs use to fit their 11 and 12 inch wide rims. or like 18x10 -25

it also helps that your running 17s. you can fit those alot easier since the actual diameter is smaller.

im running 18x8 +20 and 18x9 +20 on my s13 coupe. when i get it running and ride hieght figure out ill post pics.

if you have any questions feel free to PM me or post and ill try my best to help.