Nice route through quiet and beautiful valleys and over 3 passes. The last pass involves a longer section of pushing and only makes sense with a mountain bike and little gear (bikepacking),
Start is in Tsetserleg (not the capital of the Archangai-Aimag in the south, but rather the Tsetserleg in the north of the same Aimag). From hear you go straight south over two nice passes. Great track here that is very nice for riding.
Close to Telmen you will cross the main road that was under construction in 2017. After Ider you will follow beautiful, remote valley to the foot of the pass. Quite some river crossings here. The trail finally becomes a horse trail and for the last 200 verical meters is very steep and rough (pushig). Great view of Otgon Tenger.
On the other side of the pass there is a big river crossing and then a good road from the hot springs back to Uliastay.
Mostly quite a good dirt track, with virtually no traffic. Over the last pass the track becomes a rough horse-track where you have to push your bike. Good road back to Uliastay on the final leg.
In theory easy (you follow one river up to the pass and another down to Otgon. Still I would use a GPS.
A GPS is recommended for this route.
Water is no problem, you will find at least once a day a source. Shops with food can be found in Tsetserleg, Telmen, Ider and Uliastay.