We just acquired a 98 Gl/Sidecar rig. It's going to need tires and soon. What is the current choice for the rear? A search here brought up a recommendation for the Austone Taxi tire.
I have a 95 GL1500 with a Hannigan astro 2+2 and get excellent mileage and handling using a Goodyear Assurance 175/60 R16 on the rear. I get 21K on this rear tire and I am on my 3rd one. This tire is about 3/4 inch smaller in diameter than the original tire and changes the Rev's about 300 RPM higher in all gears. No effect on gas mileage since the car tire has much lower rolling resistance. I like the higher Revs, since at about 35MPH I was always sort of between gears and the smaller tire fixed that.
FYI I also use a Continental 130/70-18 M/C Bias ply ContiGO on the front. This is a rear tire that is mounted backwards since it's on the front. It has about 1/8 inch deeper tread than a front and I get about 11-12K on these.