I live just north of Glasgow, my favourite three big routes from the door are:
– Cowal peninsula (over to Clydebank, Erskine Bridge, Gourock, ferry to Dunoon, Tighnabruaich, Otter Ferry, Hell’s Glen, Arrochar, Balloch, Drymen, Strathblane, Campsie Glen)
– Anniesland winter bunch route (Anniesland, Dumbarton, Cardross, Helensburgh, Garelochhead, Rosneath peninsula, Whistlefield, Loch Lomond, Balloch, Drymen etc)
– Trossachs 3 lochs (Lennoxtown, Fintry, Kippen, Thornhill, Invertrossachs, Loch Katrine, Stronachlachar, Aberfoyle, Lake of Mentieth, Buchlyvie, Drymen etc)
Loads of options within those routes, Cowal peninsula has some great roads and nowhere’s busy.
Arran (ferry from Ardrossan) can be a great ride, although south of Glasgow.
Perthshire’s got great roads and is easily reachable going via Stirling and Bridge of Allan and you can head back to Glasgow via the Trossachs.