I've visited arrilas about ten times or so and have hired a bike each time from Pegasus cycles in San Stefanos. It's situated underneath the Condor bar.
The bikes are about 5 euros a day and good enough to do rides of 50 miles or so around the island.
If you ask Nicos (the owner) nicely, he may let you take a bike away at around 5.00 p.m. and return it the following day before 5.00 p.m. Try to get the majority of your miles in before mid-day.
I've never seen a road bike for hire in all the time I've been visiting Corfu.
I've toured the central and northern areas of the island extensively by bike over the years, so if you need any route recommendations please ask.
Be aware that you are unlikely to find many flat areas on the island, except for the Ropa plain.
The views from the mountain tops however are fantastic.