A 21 mile loop from Auchterarder to Kinkell bridge, bypassing Crieff by taking the unclassified road to Gilmerton, through New Fowlis, then south through Madderty and Dubheads to Kirkton, then back west to Kinkell bridge to retrace on B8062 to the start.
Great scenery, and a possible short detour uphill to Fowlis Wester to the 13th century church to see the 8th century Pictish stone.
There is a similar longer (39 mile) route in the Collins "Cycling in Central Scotland" book - it goes through Findo Gask and Dunning (another fine church here) and returning to the start via the B8062. This road passes a monument to Maggie Wall who was allegedly burnt here as a witch - but there is no record of her trial and conviction, despite records of witches being usually very carefully kept.
Hills are easy except if you climb to Fowlis Wester. There is a 50 metre ascent between the B8062 and Gilmerton.