A month or so ago I switched from very worn out DHF's to new DHR II's. By very worn out I mean just about bald in the rear with side knobs falling off and rounded knobs with rubber already hardened on the front. To my surprise I barely noticed any increase in drag with the DHR II's. If anything they seemed to roll better. There wasn't any science in this, just feel. It might have just been me happy to be on sweet fresh tires. I have a race on a very pedally track coming up and I'm wondering if the bald tires would work better. I don't really have time to experiment before the race. If no one's tried this or has a pretty decent answer I'll probably come back to this thread with some testing results in a week or two.