Things start to get complex when you start to move weight up… That is a large bulky tire, about 350#, that you now must lift, move horizontally far enough to clear the cab then lower now at least 10’. lot of added stresses with overhung loads, and the design is critical. This is not even considering the structure required to distribute that weight to the cab structure. Another thing to consider is these cabs are pretty fragile as it is, do you really want another 400-800# decelerating/delivering energy to the cab above and behind your head if you should run into something?
If I were going to do it from the cab roof, I might consider some form of A frame. Triangles are our friends, and multiple load paths are even friendlier to design for. If you did the roof structure right, you might could fit on on each side and put up the A frame on whichever side you were swapping a tire from…
If it wasn’t so tall, I might actually consider putting it up on the front bumper(lots of good solid structure, simple lift), but I think it might block too much view to maintain a good entrance angle. I am going to put mine at the rear, just high enough for the tire to clear the rear exit angle. Been brainstorming on this for a while and if I could get it lower I would
as it is though, there is no horizontal movement required, and it will be a simple straight raise and lower to it’s rack with a winch. I can also tie large steel from it’s mount location down to the habitat frame…
If I am changing a tire on demand, somewhere other than my yard, on perhaps a dark and stormy night, the last thing I want to have to do is erect a gantry for crane ops…
My .02