Long-distance trains:
According to the regulations every passenger may carry up to 36 kg (50 kg for the 1 class). Bicycles should be demounted (at least wheels, pedals, handlebar) and covered. The main problem is to find place to keep especially if there are more than one bicycle. In the 3 class it is easier because there are special luggage berths there.
Commuter trains (electrichka):
Bicycle tickets fare is about 1 Euros. No special cars or place for bicycles. In some trains there is a lot of space, in some space is very limited (you should apply your creativity to put your bicycle).
This tip is provided by supplier M05728