I am running 32mm Schwalbe Pro Ones on rims with 25mm internal width (pretty wide). I like 'em a lot. There is room to go up to 35mm in the front, but that could be a little tight in the back. I have about a 2mm gap between the tire and the two brake bridges, which is enough, but I wouldn't want to get any closer. Those wanting a little more comfort on their V20c could do a 35mm up front and a 32mm in the back.