Large parts of this route have already been paved. Nevertheless a fantastic ride across an extremely divers landscape. Some very long climbs in the east make this route a challenge.
Since April 2008 it has become impossible to enter Tibet individually. That is when mainly the checkpoint have been reinforced with army personal. Because of that it is no more possible to enter without permit as it used to be for many years. This applies for the whole of the TAR.
The situation changes constantly. Best is you get accurate informations from other cyclists that have just cycled this part. In late 2005 I cycled past Bayi and Nyingchi (km 4250 to 4205) at night and all other bigger towns during the day with short shopping stops. In the bigger places where there is a PSB presence, I would not stay overnight. But there are some accommodation option outside these places that are safe.
Best ist spring (march - June) or autumn (september - november). I would not travel this route in the raining saison (july - august). Besides the muddy roads there are many landslides that are a real danger. When I cycled the route in november I have not met a single other cyclist (although there are supposed to be quite some on this route). Is is already colder but the views into the mountains are fantastic.
Supplies are never a problem. Many possibilities to buy. In the bigger places the selection is quite good.
Along the road there are quite some places with guesthouses, truckstopps or hotels. I would not take a hotel in the bigger places because of the PSB. Camping is nowhere a problem and always fantastic! The first time I took a room after Lhasa was in Zhongdian...