For a sensible extension to the Croft Trails make your way about 1k along the road and follow tracks from Fordie up towards Braefordie (shown as some ST on the 50k map tho it is a mix of old tracks). Just past the lochans before Braefordie (not on the map) you will see a grass track climbing to the W. Follow that for a fantastic descent back down to Balmuick.(also shown as ST on the 50k map tho it is also a mix of old tracks). You can then pick up quad tracks to Laggan Wood and Twenty Shilling which do have single track paths though very busy with walkers. Ask the guys at the Croft to highlight the best options on the map. (25k will be useful)
For a more strenuous option you can head over to Lednock and do the Coineachean Circuit – tho the ascent will only be done by the strongest – all on rough landy track. As Crispin points out there are a load of other low level tracks in there.
Ben Chonzie is also an option either by the main tourist route – or if you really like hike a bike- straight up from Lednock. I’ve been looking at the possibility of a circuit off Chonzie and over to Carn Chois – but googling to date suggests it is mostly heather and bog trotting.
Scotroutes option is doable (go C/W) but it is nearly all tarmac to reach the N of Lednock and requires at least an hour hike a bike on each leg (and some serious navigation) so is a committed day. I did it 8 years ago and haven’t been tempted to have another go. (My son was on a Bullet built for downhill so was well knackered on the carry a bike bits)
SwissO1’s route through Callander is a good outing tho a lot of tarmac and also a big day NB Glen Ample is now a motorway (tho this does mean you do the main valley in about 10mins!) There are ST options through Glenartney and under (or over) Callander Crags (to cut out the town)