If you go on the Dark side board you will see all kinds of suggestions and posts about that subject. Myself I am running a Pirelli P1 R/F in the 195-55-16. This is my 4th different brand of tire and I like it by far the best. Lots of guys have more experience than I do on the subject though.https://gl1800riders.com/forums/15-darkside-riders/?action=forum
I went with the Yokohama Avid Envigor ZPS since it's a run flat. Also has symmetrical tread so I figured that could help being that tire rotations don't apply to motorcycles. Size is 195/65-16. Run flat option is important in case of a blow out. I also upgraded to metal valve stems.