Loch Lomond is the largest lake in Great Britain by surface area, and its character changes sharply from south to north. In the south, around Balloch and Luss, it is wide and dotted with wooded islands; to the north it narrows into a long, steep-sided, Highland fjord overlooked by Ben Lomond. The loch lies inside the Loch Lomond and The Trossachs National Park, Scotland's first, created in 2002. Helensburgh, Balloch and Garelochhead are the nearest towns.
There is a geological point worth knowing. The Highland Boundary Fault crosses the loch here, and the chain of islands such as Inchcailloch follows it, which is why the south feels like Lowland Scotland and the north like the Highlands. The old song about the bonnie, bonnie banks has made the place famous well beyond Scotland, and walkers from Glasgow have been heading up Ben Lomond for generations.
The riding on the west shore is by the A82, and honestly it is a difficult road. It is narrow, twisty and busy, with several stretches where the limit drops and where the loch is hidden behind trees. It is a road to take at a measured pace, enjoying glimpses of water through the oaks rather than pushing for time. Coaches and campervans often slow the traffic, and Friday evenings and sunny Sundays can be congested. Early mornings are far better, with mist on the water and the road to yourself.
The woods here are old oak, birch and hazel, rich in ferns and mosses thanks to the damp Atlantic climate. Red deer and feral goats live on the hills. Luss is a pretty conservation village of stone cottages on the shore, handy for a coffee.
For fuel, Helensburgh and the towns of the Vale of Leven are the safest options, so fill up before you start the long northward run toward Tarbet and Crianlarich. Beyond Tarbet the road climbs toward Glen Falloch and the real Highlands, and fuel stops become much further apart, so plan accordingly.