The only place really Heckler worthy would be Poldice – plenty of choice there, but in a quite small area, so no long rides unless you join them up and know where you’re going. You may find small bits of riding in various woods, but it’s mostly footpaths rather than bridleways, and even then they rarely join up without lots of road sections.
The coastpath is very good riding, but it’s starting to get busy down here, and with so many walkers about it’s not worth bothering – save it for the dark winter months.
Lots of nice quiet roads for the road bike though…