How many hours from Mae Hong Son to Chiang Mai via Khun Yuam - Mae Chaem road? Also, while looking at a map it seems there is a 'shortcut'. Just before Sop Wak take the road to Mae Chon Luang, then to Nong Tao and onwards to Sanpatong. Anyone ever used this road? Can it be done in a saloon car?

I haven't done that entire trip myself but I've met a few dirt bikers who have. I've ridden my bike in from both directions but never done the complete trip. Although highway 1263 is shown on most maps there few if any road signs when I was there and it would be easy to take a wrong turn. Even my GPS was only of limited help without a back-up map with co-ordinates on it. I'm sorry I can't be of more help. If you can speak fluent Thai and make yourself understood it would help, but don't expect any rural Thai to read the most simple of maps. They just don't understand the concept. The roads I was on were actually quite good, although somewhat narrow. I would bring extra gas in case you get lost.

I did part of the route you are describing about 3 yrs ago on a honda Dream.

The 1263 out of Khun Yuam was very good but as Rene says, narrow winding & few road signs.

I think you can forget the short cut, its very likely to be a mess in places.

Take a look at the GT rider forum, they will have the best info, sounds like you have the Mae Hongson loop map already.

I do not have a road map in front of me, but if you are turning east before Mae Chaem and going around the backside north of Doi Inthanon to drop down into Sanpatong then the answer is no, that is not a road for a ordinary passenger car. Even the paved road connecting Nong Tao with the 1013 that takes you down to Mae Wang is often heavily potholed, you can drive it, but it may be slow going.