Cool trip. I took this route on my first time in China in 2007(but on buses). The road from Kangding to Litang at that time was possibly the worst road I've ever travelled on- shook the bus so much that the windscreen bounced around in it's housing and the last seat from the back was shaken so much, the metal legs snapped where it was welded to the floor, leaving it's foreign occupants sat on their bags in the aisle, although they actually thought it was hilarious . Our visas nearly ran out in Litang but there was nowhere to renew them, so we had to go back to Kangding and do them there, so actually ended up travelling that rutted mountain road three times. Would be awesome by bike I'm sure especially with your mates.. Six of you , right?
The scenery was great going through the mountains and the Tibetan areas.
I met a traveller recently in Kunming who had travelled the road and said it is all sealed now.