You could try coming out of Truro, through Shortlanesend. Across the A30 in the Perranporth direction. You could carry on to Perranporth or cut through Mithian to St. Agnes (where you should detour to the Driftwood Spars) On to Porthtowan and Portreath, where you can pick up the Mineral Tramways cycle route to Carnon Downs and Back to Truro.