There was quite a bit of discussion a few weeks ago about what kind of traction KOP wheels would have on 'diamond plate'. We drove a robot on our ramp this past week and here's the video
http://www.youtube.com/watch?v=qyTBvyRluOs. As you can see from the video there is more than adequate traction to slowly drive a robot up our 20 deg ramp. Since traction is coefficient of friction times normal force, robot weight is not a factor, that is if you've got enough power to do it in the first place. Btw, the ramp robot is a rookie team's that our team is mentoring