Highway Comments:
Karakoram Hwy - From Kashi to the Pakistan border, the Karakoram Highway on the Chinese side is, as of 2007, under construction. Much of it is brand new sealed pavement with some graded roads in between. Currently, about 70 percent is newly engineered and paved so water hazards are minimal. Where forced to use the old road, expect plenty of sand and rocks. Considering the amount of construction work, it should be totally sealed by 2008.
Lanzhou to Urumuqi (312) - This is the virtual "backbone" of China's transportation network (so it carries lot of trucks and busses) to NW China and also runs parallel to train tracks. From Lanzhou to Dunhuang expect some horrid and long stretches of road works. After that, it's smooth sailing. 312 is the only good road in and out of NW China. The other is 315.
Lhasa to Chengdu (318) - Very possible by motorcycle and takes you through amazing landscapes. Going west, past Litang, it gets progressively worse until you reach close to Lhasa.
Lhasa to Golmud (QingZang Highway 109) - About 90 percent of all traffic that goes to Lhasa heads down this road as it's the best maintained. This road averages about 4300m/asl and can be very remote, cold and wet any time of the year. Also, the new Qinghai Tibet railway runs parallel to this road.
Golmud to Dunhuang (109) - A nice stretch of desert road. Although not as desolate as Mangai 315, if your tank only has about 300km range I would pack extra fuel. In my KMZ file you can see a truck stop (NOT like western truck stops) where gas may be available but don't count on it.
Lhasa to Yecheng Hwy (219) - I haven't meet anyone with direct experience on this road although I know it's basically a service road and most of it may not see tar for a long long time. It runs the length of the Himalayan mountains near the border of India and given the conditions of other more thoroughly maintained roads in Tibet, this one is bound to be rough. 219 is one of my dream rides but I've been told by very experienced riders in China that you should not travel this road alone.
Qumalai to Budongquan - One of my personal favorites and where I got my first taste of serious river crossing. The road is nonexistent and in places becomes river bed. Finally, it meets the QingZang hwy just before the Kunlun Mountain pass. The trick to this road is the weather. If the weather is good you'll have the off-road time of your life surrounded by amazing wild life at over 4000m. If it's raining daily, then I hope you can read rivers and don't mind getting wet!
Xining to Kashi (315) - Besides 312 mentioned above, relatively beaten highway 315 takes us from Xining to Kashi (Kashgar) . In particular there's a stretch near the Xinjiang border (Mangai) with incredibly bad but wickedly beautiful landscapes and is notorious for truck toppling winds. Campers take note, all natural water in the region is salty so pack your own water and fuel.