If you need to rent a bicycle when trravelling Ishigaki downtown area or Taketomi island, here is some reference for you to check out!
石垣島レンタサイクル (Ishigaki Rent-a-cycle) is located within the port terminal building (very near from the room!).
友利観光 (Tomori Kanko) has been operating the renting business for a long time on the island and has many variations of bicycles.
Please try it!