Just for more information, the CTF cars typically have "winter" tires put on in place of summer or hi performance tires on the RWD cars if they are assigned over the winter months. This happened on the GTOs, CTS-Vs etc. that I've driven in the past.
Note in the lower drivers side windshield the cars have the CTF sticker.
In my experience, we have usually just used a local tire store so glad to see a local GM dealership get the business.