My wife told me about a "motorcycle road" that she had driven and this weekend, I got to drive it wishing that I was on the bike. It had 49 curves in 8.8 miles making it fairly interesting. 49/8.8 = 5.56 CPM which I think we should use as a road rating factor. I'm glad that I have got my wife "trained" to watch for roads like this. Plenty of curves for interesting riding and decent enough surface for street riding since I don't do dirt.