275/50R15? - wow, impressive, you must have got the backspace and offset very well sorted. That will have an impressive musclecar stance.
On my car the existing 14"x7" rim with 4" backspace and 205 tyre has about 8mm clearance at the guard lip.
Checking with an online calculator, a 225/60 tyre on a 15"x8" rim with (typically) a 4.5" BS will give a width increase of 10mm both inwards and also outwards.
I could trim back the wheel arch trim piece which projects inwards a little and gain a few mm at best. But it will be of marginal help.
So I'm curious to know how people go about fitting say a 235 let alone your 275 without guard surgery, lip rolling etc. Or custom rims.