Only the coupe has 10" wide rears.
That is good to know. I bought a set of coupe wheels for my wife's 2010 CTS wagon when we bought it 2 years ago.
We took the wheels off and traded the 2010 CTS wagon in last week for a 2014 CTS-V wagon. The two drivers side wheels on the CTS-V have curb rash.
We checked the tire size on the wheels we have and the ones that came on the CTS-V and they are the same size.
She was wondering why the wheels on the CTS wagon stuck out a little more than the wheels on the CTS-V wagon.
Now I know why. The rims are wider. She will be happy. She liked the look of the wider wheels.