(added after the original post) For the most up-to-date information, please read this article ARTICLE: Update on how to enter and cycle into Tibet independently? Checkpoints, Elevation Charts, Route Descriptions, Links, Maps, Aerial Picutres
I can give you some info and links but everything I know is out-of-date. It has already been several years since I biked to Lhassa. I took the Yunnan Highway, but I know some friends who took the northern route a few years ago.Checkpoints on the road (Kermo) Golmud - Lhassa
travelogue from Asiemut: "We entered Tibet via Kermo (Golmud in Chinese) since we came from the Taklamakan desert (the Xinjiang province). The access roads from Kashgar, Xining, or Chengdu seem more interesting because they are not as used and they are more diversified, although we don’t have precise information on this ways.
The Kermo/Lhasa road is completely paved and used by many (trucks, jeeps, police cars, army vehicles). Sometimes, it gets event hard to breath because of the toxic fumes. So it is definitely not a Sunday drive into the country! This road takes you to 5700 meters of altitude and offers a panorama that we truly enjoyed. There are many Tibetan villages along the way, starting approximately 600 to 700 meters from Kermo.
The first checkpoint is five kilometers from downtown Kermo, immediately after the Petro-China plant. It is obvious because all cars have to stop there. We went around it on its right side, getting as far as we could away from the road. The landscape is rough and sandy.
The second checkpoint is 40-45 kilometers from Kermo, and very hard to go around cycling in daytime. We did it at night, following the wall on the right side of the checkpoint (which is about 150 meters from the officers) to then pass alongside the gas stations located after the checkpoint. It is impossible to go further right, since a hydroelectric dam blocks the way.
On the road, tons of police cars passed by us without stopping. We had food supplies for many days and went by the cities without stopping for too long. We always found a hidden camping spot to spend the night.
Contrary to what we heard, there was no checkpoint 450-500 kilometers from Kermo (close to Marchudram Babsuk or Tuotuohe), but there was one at Amdo, which was only a weight control station for trucks, cars could simply pass by on the left (also easy to do for bikers). The checkpoint at Lhasa was closed when we passed by because of the weather, but other travelers told us they also went by easily.
Hence, we reached Lhasa quite easily. Water is abundant on the way and you can get quick noodles in villages (being discreet, of course). The new railway can be used to protect yourself from bad weather (snow, rainstorms, and strong winds) and also from curious eyes at night. Rain is common on the Tibetan plateau in September, event though the “real” rain season is supposed to be from June to August."Here are a few links of good websites for biking into Tibet
Again, some info is quite old, especially concerning the road pavement (I am sure you know these sites, but it might help other readers):http://fred.ferchaux.free.fr/
It is mostly in French but there are a lot of tables with a LOT of info that one can use even if they don't speak French.http://www3.utsidan.se/corax-e/
Janne knows Tibet like the back of his hand... he has biked most Tibetan roads. Great elevation chart. Some good links.
I have a friend of mine who lives in Lhassa who he is also a cyclotourer and I will try to contact him to find out about the current situation. I will let you know.
I heard that it is more difficult than prior to 2008, but that it is still possible to enter Tibet illegally from the Yunnan or Sichuan Highway. You might want to consider this option since it is a more scenic route.
Anyway, if anyone has any recent info, please share it here...