Hey Ross,
I will get panned for saying this but I had a Venture before the FJR and some guys that darksided their ventures or goldwings, voyagers, etc also put a rear tire on front for longer life. In order for this to work they had to put the rear on the rim so the tire would rotate "backwards" because of the design differences between front and rear tires. I'm not recommending it and I'm not sure there is a rear size which will fit the FJR. Lots of discussion on this on Venturerider.org and other sites.
Maybe you can be the first 'rearsider'.
FWIW
Rick
I also had a Venture before I bought the FJR! I never tried a CT on that bike.
A CT on the back with a rear MC tire on the front (reverse direction) is sometimes referred to as double-darksiding. I haven't heard of anyone doing it on the FJR. While my planned trip will be long, I don't think I am going to that extreme.
From the responses I have seen on this thread, I SHOULD be able to make it with a new PR2, PR4GT or BT023GT as long as I keep total mileage to something less than 15,000 miles. If I find myself running out of front tire before I'm ready to come home, I'll try to arrange a tire drop-ship to a willing forum-ite (with a tire changer) and deal with it on the road. Otherwise, a dealer visit will be in order. My trip will include a lot of nice roads but also quite a bit of straight slab riding to get from one area to another.