Gotta add another vote for the Tri-comps. I've been running those on my Six13 since I got it, and I really like them. I run mine @ 130 psi, which works great for me, since I'm a heavier guy. And the fact that they're rated to 175# makes me feel better that I'm not running them close to their rated limit. They have amazing grip, and seem to be pretty tough w/o being heavy. They're not cheap though ($50+ / each). I have a pair of the regular Fortezza's that I bought, but I don't know if I'm going to use them or not, as they are 25mm and not 23mm. They're brand new in the box if you're interested in buying them. I think they were $20/ea.