Well, after reading the previous posts about this topic, i would like to share my experience. I have made this summer a 5 months trip along the silk road from France to China trough Turkey, Iran, Turkmenistan, UZ, KG, KZ and China, i was may be lucky to be allowed to go into China independently and ride from Druzba (KZ) to Beijing.
First, it seems to me important to keep in mind that in these countries, what is true one day may be wrong the next one... and before being successful in border crossing, i was turn back in the Torugart 11 days before. I knew exactly before trying at this place it was probably the most umpredictable border from central asia, but i was so near (Tash Rabat), and i have a double entry Kirghyz visa, then i decided to try.
Without any surprise, they don't let me cross the border, but it could have been possible an other day (i was there on friday and they will close soon for week-end). This may have work only if i have book my journey with a chinese travel agency which will provide me a guide to Kashgar... etc, etc. A chinese guide who was there to pick-up some tourist can provide me this service for 150 USD, and except this no way !!! In fact, the most complicate was to cross the first checkpoint, i have to talk for a long time with the guards and it cost me 20 euros to do that !!! But no regrets, i have to try !
1500km later, i face again chinese border at Druzba check point in Kazakhstan, compare to others "Stans", it was quite difficult to leave Kazakhstan ; they check carefully my papers and all my bags. After five hundred meter, i meet the first chinese post, i have to open again all my bags, they check again everything but they let me go easily without paying anything, nobody there spoke english.
The main custom office was not far, i arrived there at lunch time and there was nobody. When they come back, i was worrying a litle and in fact it was cool. A small part of the staff was speaking english, they were friendly and helpful, and all the paperwork was done in one hour, the bike was not a problem, i just have to put it on the custom declaration form and nothing more, of course no guide and nothing to pay ! i was really surprised, and when they stamp my passport, i was near to shout "YESSSSS" !!!
The officer was really intererested in my trip, and something which seems very important for him was to show him i have a map, and also I know exactly where i was and where i plan to go ; my feeling is that he wanted to be sure that i won't be lost as soon as i leave the customs. After shaking hand, he wish me "have a nice trip !".
What a strange feeeling when i leave this place, i was so happy, but in other hand i feel a little bit lost... and frightened by this huge country. I don't ride more than 5 km and police stops me, it was fun, they doesn't expect to find a people like me under the helmet !!!, they just check my passport and let me go. This is exactly what happened each time the police stops me on the road during the month and half i spent in china. We cannot communicate et they don't know what to do with me. During this kind of control, asking to confirm the road and showing the map was a "sesame".
There is just one exception, one day i was on a trail in a remote area in Xinjiang, the police stops me in a village, they want to see my "permit", i have nothing and of course they don't want my driving licence, they look very angry and ask me to go back from where i was coming, one of them which seems to be the chief told me "Go back to Kazakhstan !", but they don't do more, i just have to go back and find an other way, it was on trails in high mountains and this day it was not far from midnight when i arrived in Balguntay
My feeling is that Chinese authorities don't want to have any trouble with foreigners, in my opinion they want to behave like a big democratic country and they don't really care if you are or not compliant with chinese road regulation. Except this problem in Bayanbulak, i was really free to move and usually policemen were more interested to play with their mobile phone along the road than checking my papers, very often they stops chinese cars or trucks and let me go. In many occasions, they help me to find my way.
One day, i meet on the road in Gansu an english guy, who was living and working in Beijing. He was travelling with a 3 wheel cj750 through China, and doesn't have any bad experiences about driving in China.
In other hand, i think i could be in deep trouble if i was involved in an accident, but this was also true for many countries i have crossed before, and it's so great to travel like this, then…
At least, i believe the most important is to keep smiling.
Sorry for my poor english ;o)