Did it 2 years ago, gravel bike will be fine although HT might be more fun for certain sections like the long descent into Helensburgh. Watch out for Her Majesty’s troops practising around Garelochhead area 🙂

We turned it into a 2-dayer, taking the ferry across to Inversnaid, overnight at the bunkhouse and then through the Trossachs, via Loch Arkle / Chon / Ard into Aberfoyle, then Rob Roy Way and Sustrans 7 back to Balloch. Two cracking days!

ps. can PM Strava routes if interested

I did a small section earlier on this year the bit from arrochar to Inveruglas, as part of the glen loin loop, i noticed all the signs for the 3 lochs way so it seemed pretty well sign posted. For the bit I did you would be fine with a gravel bike although, the were a couple of rougher bits that would be more fun on a HT, but they were definitely in the minority. It was quite a nice ride and I can imagine the views would have been amazing but unfortunately it p*ssed it down for me all the was around and I couldn’t see a thing. I’d definitely recommend taking a little detour up to Loch Sloy though, before you drop back into Inveruglas.

I made a little video of my ride that I did.
[video]https://youtu.be/cyE0CT7qEB8[/video]