Mongolia offers fantastic cycling opportunities especially for those who like rough tracks through remote areas mixed with plenty of adventure.
Good roads only exist around Ulaan Baatar. Very soon they become bumpy sandy tracks. Although many of the major transit roads have been upgraded and are now paved.
I was very impressed with the diversity Mongolia has to offer. Not only are there sandy derserts and grasland but lots of lakes, wide forest and marsh land can be found too.
The roads in Mongolia you could put into three different categories:
Starting from Ulaanbaatar the network of paved roads is quickly growing. It is mainly the main transit roads that are being upgraded. A lot of traffic is only in and around the capital Ulaanbaatar. But everywhere else there is not much traffic even on these roads. Even though the places that have been reached by this network of good roads are quickly changing. Soon there are filling stations, houses, supermarkets etc.
Still most of the roads that connect the bigger places have never really been built on purpose. They have just appeared after repeatedly being used by traffic. There is not much traffic on these roads but the surface is still often bad (corrugated). Very often there are countless track right next to each other.
There is a road/track leading up every single valley. They exist because people go everywhere to put up their Ger in the summer. Because of that there are turn-offs all the time going every possible way. Usually, the further up a valley you come, the less clear a track becomes, especially over the pass itself. That is because most people use these tracks no to cross over to the next valley. On these roads you find very little traffic, it is mainly motorcyclists on their way to their Ger.
These roads are great for cycling, often not much more than a track over a meadow. To find them and not get lost, you will need a GPS (because of the many turn-offs).
There is at least one hotel in every town. In more touristy places there are Guesthouses and Ger camps. But hey, this is a nomads country, so camping is pretty much everywhere is the way to go.
In towns there are good stores. Fruits and vegetable can be very hard to get in the countryside. Even little places have a very basic shop where you can get the most basic stuff.
In the southern part it is often very dry and places with water are a long way apart: plan well! In the center and north there are a lot of rivers and lakes (some are salt lakes though).
In the south every place has a well of some sort. Often located a bit outside in a little house. Here you can get good, fresh ground water.
With a visa you are allowed to stay 30 days in Mongolia. If you want more, you can extend your stay at the immigration office (near the airport) in UB. You can only extend your stay once for 30 days max. The cost is 2$ per day (2014). The whole process is straight forward and includes registration in the country.
For routes close to the border (Tsagannuur, Altai Tavan Bogd Park) you will need a border permit. Often it is not possible to get them by yourself and a local has to support you. Of course they will be interessted in selling you a tour and not only a permit which can make it difficult.
Finding a good map for Mongolia is not that easy. For the major roads a normal map will be fine (Nelles, RKH).
If you want to ride more remote routes and tracks a GPS is a must. Because of the countless turn-offs it would be difficult to stay on course without. I use OSM maps on my GPS which are good and contain most of the routes these days.