I put new Schwalbe Marathon Plus tires on my Sirrus 3.0. They're some tough tires to stretch over the wheels! YouTube videos helped a lot and made it much easier. I went with 35mm tires in place of the stock 32mm Specialized Road Sports. I had wanted 38mm but there were none is stock that I could find, but the 35's look good on the bike. Can't wait to try them out later!