So you have already decided to drive to China this year without doing any research whatsoever on something that is completely impossible?
Anyone entering Tibet needs a permit in addition to his China visa. These permits are easily obtained by people travelling on government-approved organised tours, but much less so by independent travellers. I have read stories about people managing to make their way into Lhasa by car from Xinjiang, making their way into Tibet by paying a fine at the first check point. But this doesn't sound like the kind of approach that I would rely on.I don't remember if they entered Tibet and I don't know if it has different rules than the rest of China.
The road condition is the last thing you need to worry about for such a trip. I bet with any car (as long as road worthy) and common sense you will be OK. The real problem would be to enter China -- definitely a nightmare.^^ That's difficult to reconcile with what I saw last September en route from Bishkek to Almaty (which is pretty much the last section of Kyzylorda - Almaty). That was mostly single carriageway: three-lanes or four lanes. Only some 60 kilometers before Almaty the road turns into double carriageway, even though most intersections were level crossings.