Truro is part of two national cycle routes
National cycle route 32 connects Truro with Bodmin via Newquay. Including the Camel Trail.
Nearby Truro, there is also the Mineral Tramways route between Devoran and Portreath, which connects the south coast of Cornwall with the north.
For more information, go to the Sustrans website below where free maps can be downloaded.
Cycles are often welcome on trains into Truro, although it is best to check specific train company policies : http://www.nationalrail.co.uk/passenger_services/cyclists.html.
There is also a bike park at the Park for Truro site at Threemilestone. A covered cycle stand for you to leave your bicyles on site.