Tire/Wheel Staggered but not?

[skiboats]

I have a 2001 4.4 with sport package. It has style 63 OEM 19in wheels. I had not paid to much attention to them as they have been off for the winter.

What I have noticed is that all four tires are the same size. Continental 255/50/R19's. They are OK for now but will probably need to be replaced before too long.

Is it possible that the wheels are staggered as the manual suggests and that narrower tires than specified are on the back? Would they fit the bigger wheel?

Or is there a chance that the wheels in fact are all the same size? Is there an easy way to tell what size they are with the tires on?

Manual says Front 255/50/R19 Rear 285/45/R19

Sorry for all the questions, just wondering why they are all the same.