ii did not bicycle tour in vietnam, but spent a month backpacking through there. if your inquire is about the conditions of the roads (sealed vs dirt), the route up the coast from saigon to hanoi is all sealed. if it is a matter of gears, the area around nha trang and dalat gets mountainous and may be difficult to climb with racing gears.

i was in vietnam for around two weeks last june and the first thing I thaught was this would be an amazing place to ride my bike. KIts crazy yes there are lots of mountains but the contrast is crazy because you have huge pillar mountains then booooom just flat land for farming. thee is one main road from hanoi in the north that runs along the coast and then inland again to ho chi mihn city. i did it by bus. But there is food all along the way and lots of warm beaches if you bring a light sleeping bag ad maybe a bivi sack with a face net. It would be amazing! Im going to do it one day.