Rentals are almost as a rule in dreadful condition.
You might want to take your own saddle and buy a used bike and then sell it when you leave the country. According to two friends of ours, this is THE best way to see the world. They said that sometimes getting from place to place was difficult because people would invite them to stay with them all the time. In Fiji our friends said most of the time they would just wave and not stop, otherwise they would end up having to stay in every village and house along the road. Nevertheless, they have met many more local people on their 8 month trip than we did going by public transportation.