There are about 55 miles of well-maintained, endlessly beautiful Carriage Roads on Mount Desert Island for hiking, horseback riding, and bicycling. No motor vehicles are allowed on these hard packed, all weather roads. You can rent bikes in town for a half or full day ...or more, and pedal about on any of these trails. Some trails have moderate-to-steep grades, others are easier. You'll definitely want to consult a trailmap which is available in the Campground Store.
While a Cross or Mountain Bike is best for the Carriage Roads, there really aren't any trails on the island for Mountain Bikers. All hiking trails are for foot traffic only.
The free Explorer bus has bike carriers to transport your bike from either the Campground or Bike Rental Store to the Carriage Trails if your car isn't equiped with a bike carrier. (The Carriage Roads are several miles from both.)
The main roads have wide bike lanes on both sides, but the narrower roads near and through the Island's villages are not the best for bikes! The Loop Road in Acadia National Park is a great bike ride at 11 miles... mostly two-lane, one way travel.
So, bring your bikes... or rent them here, and enjoy Mt. Desert Island up close.