I thought I would post results of my conversion to 19.5" wheels and a 14 ply tire. I have a 2004 Kz toy hauler that I have had since new. I have had zero problems, except tires.... First the oem tires, not sure what brand they were, but 2 blow outs and a lot of body damage on one trip to Florida so all new tires, hankooks, I know, not a good choice but I used them on some of my other trailers without problems. Then again another trip to Florida, three tires on one trip..... More body damage. Then to goodyear marathons, 2 blow outs on a trip to Kentucky. So now on to 19.5" after quite a bit of research and some work. I had to lower the springs and move them out on the spring mounts to gain some space and height. Then I braced the perches with welded channel connecting the spring mounts. Worked out perfect! I just got back from a 2400 mile trip. The trailer is much more stable, less bounce, and I gained a tad over 1mpg on the entire trip! Couldn't be happier! Don't hesitate to ask any questions! I would recommend it to anyone thinking about it, no tire worries anymore!
Here is a few pictures.
Here is a picture of the TR