We had a tough time finding information online in English about where to rent bicycles in Yerevan. Locals pointed us to a stand in front of the Marriott in Republic Square, but unfortunately none of the bikes there were in good shape to be ridden. We found this Bianchi store randomly and rented PERFECT new beautiful bikes there for very reasonable rates -- 1500 dram an hour [less than 3 euros] with discounts for more than 3 or 5 hours. They are centrally located, easy to find, speak English, and were super nice people. Skip taxis and cars, I highly recommend renting bicycles here and exploring Yerevan on bike. It was definitely a highlight of my trip and it's not bad riding at all in the city even on the main roads, people are respectful (or at least nonchalant) to bicycles. Enjoy!