There are other brands with tires for the GL1800, like Metzeler, Dunlop, and Avon. However, they all cost more.
I ran a few sets of Metzelers on one of my Valkyries and liked them. If the price were better I might try a set on the F6B. I used to run Avons on both Valkyries and liked them so much I tried them on the F6B. Then this bulge suddenly appeared on the front. Now I run Bridgestone on the F6B and both Valks.
My buddy has a big full dress Harley, he runs the 777 Shinko tires and he loves them, I am not sure about milage or anything , but he is a guy who looks for bargains and he says he will buy them again.