Try and ride all the red ones. they are great and why we live here

http://www.coloradodot.info/programs/live-to-ride/rider-resources.html

Couple sport bike friends of mine worked with the state a couple years ago to come up with this map. It's pretty accurate.

I've done everyone of the red roads (and most of the others) with the exception of 141 between Naturita and Gateway. Gives me a goal for this summer.

I agree that most of the red roads are fantastic (twisty, steep, scenic and therefor more difficult) but some are not. Example is 83 from Franktown through Parker or 82 from Glennwood Springs to Carbondale. I guess they must be considered difficult due to traffic but then any 4 lane through a busy area would qualify.