Argy: I believe this is the Thunderbird you are talking about
3 cylinder 885cc retro sport bike
It doesn't have abs.
My buddy is getting one. They are a great bike with a ton of personality.
Here is their forum https://www.triumphrat.net/hinckley-classic-triples/
This forum is for this version:
2 cyclinder 1600cc cruiser
But to answer your question:
Metzler Tourance tires would do fine on highway and gravel!
Here they are on my bonnie: