An easy bike ride by the loch, mostly cycle path; not circular.
This is a very pretty bike route and almost flat. The cycle path section is a good dirt surface. The public road on the south side of Loch Venachar only goes to a sailing club so should have very little traffic. There is a picnic site at the east end of the loch but the best picnic spots are at the other end. The other trails are mountain bike routes and these climb steeply towards the Duke's Pass.
From Loch Katrine (Trossachs Pier) - The only hill on the route is the mile between Loch Katrine (Trossachs Pier) and Loch Achray, this will have cars. Going east turn right towards the Loch Achray Hotel passing round the south side of Loch Achray.
The cycle path begins at the start of the hill. It should be marked as National Cycle Network Route 7, and also as a bike route by the Forestry Commission. There's a barrier to stop motor bikes.
After this you go along by the south side of Loch Achray, there may be an occasional car for the first mile. Turn right just before some old farm buildings. If you keep straight on you cross the river.
Going east after this bear left at any other junctions to keep beside the river. The path winds prettily through trees and soon you see Loch Venachar. When you eventually get to Callander you meet the A81 Glasgow road, turn left to cross the river and enter the town. Just before you enter Callander you pass Trossachs Backpackers (accommodation) who also do cycle hire.
From Callander - This would be a great little cycle ride for children starting from Callander. You could go for a picnic in the woods at the west end of Loch Venachar, or have tea at the Brig o' Turk Tea Room.
In Callander take the A81 road signed Glasgow to cross the River Teith then turn right to a minor road where the main road takes a sharp left bend. There is a caravan site half a mile down this road so there will be some traffic between it and Callander, but after this the road should be quiet.
There is a picnic site with a small car park as the loch comes into view, a couple of miles after this the public road ends. You turn right off it following the bike route sign. This leads you through trees by the side of the loch for several miles. After the loch bear right at any junctions to keep near the river. When you come to the T junction with farm buildings near it you can turn right to go to Brig o' Turk, or left to continue to Loch Achray. and Loch Katrine. After Trossachs Pier the route by Loch Katrine is car free.