On rear you want +40! As long as you don't go really low then you will be able to get a 275/30 on the rear (prob even 35 profile) without any guard work. Once you go to 285 then just a roll and slight pump will clear. As for the fronts anywhere between +25 and +35 is generally pretty safe. The +35 will be super safe even if the car is lowered heaps. +25 should work even with a bit of low, just might need the inner plastic moulded out a little (maybe, it should be right without it) Here's a calculator I found to work out overall rolling diameter. ((width x profile(%) x 2) + (wheel diameter x 25.4) So doing this a 245/35/19 = 654.1mm rolling diameter and 275/30/19 = 647.6mm. Now a 285/30/19 = 653.6mm. So going off that a 245/35 and 285/30 is the same so yes a 285 would be better. I think you might have read a lot of posts that people run 275/30 on a 20" wheel At the end of the day though these are just rough figures and I've heard of differences in width of a 275 tyre being up to 20mm wider than each other because different brands have different shoulders etc.So when shopping around probably consider the width of the actual tyre when choosing between 275 and 285