kirban 2 cents worth
Several factors figure into tire size front and rear in the 16 inch.
The good thing is you got four front GTA rims.
Not sure what year Turbo Regal you got but any year but 1987 sat lower in the front.
So if you have a 1984-85-86 you need to upgrade your front springs.
All years you need to have replaced your rear springs as factory springs are not the greatest....if in doubt put two of your large buddies in the back seat and see how the car squats down.
The key feature on rear tire fit is how straight your car is on the frame....not many were even when new now add 20 plus years to the mix and unless you have replaced every body mount and had a body shop do it on a frame rack I betcha your car is not on the frame straight.
The clearance problem arises on the tire and the outer frame rail and or the lip area of the quarter panel.
My opinion...stick with the GNX rear tire size 255/50s and 245/50s up front...
Also complicating things to a lesser degree is not every tire in the same size is exactly the same width....
I run 245/50s all around.....
Granted today 18s are more common but unless you wanna outlay more money and take chances that is the way to go.
denniskirban@yahoo.com