Great ride through the Khanhai Mountains and over the 3000m high Nuhem Davaa, passing the holiest mountain of Mongolia, the 4021m high Otgon Tenger.
Mostly a good dirt track only the descent to the west is a bit bumpy.
From Tariat follow the northern shore of Tsagaan Nuur. Park entrance 3000T just after Tariat. In the park you first follow some lava fields (bumpy). There where you actually meet the lake for the first time are many Ger camps. Further along the coast there are many beautiful coves, great for camping and swimming. About 10km before Tsahir you meet the main road that was just about to be paved in 2014. After Tsahir you enter a long, wide and rather barren valley. There are many small streams that come from the north and which you have to cross (no problem). Finally the track goes straight across a meadow up to the 3000m high pass.
On the other side it is at first also over meadows. The track seams to be much less used on this side and is rougher. Just before you can see Otgon Tenger there is a bigger river to cross. In Otgon there are simple shops and you meet the 'main road'. A good dirt track climbs up to a high plateau. In the downhill the surface get worse and worse. The last pass before Uliastay has a very good road again.
Mostly quite a good dirt track. A bit more bumpy in the downhill to the west. The worst part is in the downhill after the high plain (after Otgon). Between Tsahir and Otgon there are only few Gers and few vehicles that go to them. Over the pass itself there is virtually no traffic.
In theory easy (you follow one river up to the pass and another down to Otgon. Still I would use a GPS.
Some Ger Camps at Tsagaan Nuur, elsewhere only camping.
Water is no problem. Between Tsakhir and Otgon you pretty much constantly follow a river. After Otgon there is a stream atop the high plateau and later at the lowest point before Uliastay.
Buy food in Uliastay or Tsetserleg where there are good shops. In Tariat, Tsakhir and Otgon there are simple shops with a limited selection.