I made this change on my 28' Pace Shadow GT trailer about 10 years ago and I talked to (the old) Pace before I did it. They recommended that I use 10 ply LT (light truck) tires not the ST trailer tires and they also pointed out that the wheel boxes that the factory installs in the trailers with 15" tires are smaller than the wheel boxes that they install on trailers with 16" tires. So in order to have adequate clearance they told me to lower my axles by 2" by cutting off the existing axle mount and welding a piece of 2"x3"x1/4" tubing between the axle mount and the trailer frame. It was a bit of work to do that but now I run 245-75 R16 LRE tires (3040# max load) and I have good clearance over the tires.