Just a couple of thoughts on this subject from someone who has riden through China on a bike...
We just rode through Western China (Xinjiang Province) from the Torugart Pass in Kyrgyzstan to the Khunjerab Pass in Pakistan. This was all done the "legal" way, with the Chinese driver's licence, Chinese registration and guide through a Chinese travel agency. These are the offical regulations for bringing a vehicle into China.
One thing to keep in mind is this...China is a modern country, their customs posts are all computerized and they all know the rules regarding the importation of vehicles. Additionally, the parts of China that most people want to ride through, Xinjiang Province, Tibet, etc, are very sensitive areas and visitors to these areas are under even more scrutiny.
Even if a handful of people have gotten their bikes into China, they are truly in the minority. Is it worth planning a big trip around something that has a small to non-existent chance of happening?
And what will you do when China refuses entry for your vehicle from the country you came from...you have already been stamped out of that country...if you had a single entry visa, how will you get back in??? This could put you in a real tough situation and China may very well impound your vehicle until you get things sorted out.
Of course, anything IS possible. People have won the lottery, been struck by lightning and lived, and gotten into China with their vehicle completely independently.
Just don't count on it. Its all about odds...
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Dave
www.mototrekker.com