My family bikes. We had such a miserable experience bIking on Aero we have jokingly dubbed it "the day we don't talk about".
First the bike rentals there were really old rickety bikes which had seen their better days. This added to the trouble as biking there was a workout and we could have used better bikes. Aero was not flat. And unlike other parts of the country we did not see bike lanes. Cars and trucks would pass by us at decent speeds and it was challenging because at times it was nerve wracking. On top of this we could not make heads or tails of Rick's bike map if you can call it that in the guidebook. We got so lost and nearly missed our ferry going back.
My husband and I actually said to ourselves how is it that Rick promotes biking here of all places. i imagine you are not the only RS fan who hasn't biked in years. If you or your travel partners are intent on biking here I would make sure to do some biking (uphill, downhill, dirt paths, on road) before you go on this trip.
We only found two bike rental places. One was a hotel/restaurant a short walk up from the ferry where we rented. They provided helmets although we found most people didn't wear them. They were a must for us once we got out of the ferry area and into the back country roads. There was another place that rented which looked like an abandoned gas station a bit more of a walk. We didn't rent here because they had less of a selction, we didn't rent in advance.