As Ive posted before, Im interested in some 18 inch wheels. The recommended tire size they gave me is 245/40/18, but I notice the CTS V rides on 245/45/18. I want a more performance oriented tire, but also dont want a harsh ride. Keep in mind I live in Detroit with crappy roads. Should I just opt for the CTS V size tires? They are a little over a half inch bigger than the stock size and the stock suggested size. Would this have any negative effects? What would YOU opt for? Thanks.

I have 245x45x18 Pirellis on my car. I think most of our members are running the 45 series, same as the V.

Yup, I have the same size tires as RobertCTS. They don't create problems and I have found that the speedo actually matches what GPS reports as my speed with the bigger OD wheels and tires.

I have 245/45-18s too.

Yup, what MBai2 said. Going with 245/45R18's will keep the sidewall height and ride comfort, while the width gives better performance. I also found that with the bigger tire, my speedo now matches what the GPS says my speed is. Plus they fill the wheelwell much better than the tiny stock tires.

I just got back from the carwash, were there were three CTS's and an STS all in a row. My son just said "I really like the look with the bigger tires on your car, Dad. Those tiny tires scream "grandma's car"!" LOL