Dan, I'm afraid you are right. I think the load rating is visible on the sidewalls but is not the issue. There are several different sets of tires listed in the manual but like you, I think the ROPS is the likely culprit. Gee, I guess I gotta try to keep it on 4 wheels more of the time. I have had it on several of the possible combinations of two wheels, some, multiple times. With any load on the FEL, I keep one hand on the FEL stick, just in case. Has saved me from laying it down a number of times.
Mud suction on the FEL while trying to raise puts both back tires in the air. No biggy until the suction starts to break then you better take some up pressure off the bucket.
Going through short radius cylindrical concavities where you have to go diagonally will leave you temporarily on one front wheel and the opposite back wheel and if nearly ballanced will oscillate back and forth between sides as the tires alternately catch traction. Continues until you step on the diff lock.
And of course there is the intentional lifting of both front tires with the FEL like to pour out cement better with the 3PH mixer.
Only twice have I had it on two wheels on the same side, once on the left and once to the right. Once with 200 T posts on the pallet forks and turned the wheel too far to the side. It went up on two wheels but I got the pallet forks down before it went past the point of no return. Two lessons here... Don't overload the pallet forks with respect to rear ballast like an implement or whatever and don't turn the wheel too far. It wasn't a centrifugual force thing but a wheel placement geometry thing. It tends to lay down in the direction you are turning not the other side as it would with centrifugual force. The fix? don't turn too sharply with a heavy FEL load. I guess you could get cute and turn sharply if you went just fast enough to generate enough centrifugal force to ballance the lean-in-the-direction-of-the-turn tendancy. I think I will pass on that experiment.
The time I put it on the left two wheels was because I did not walk the area I was working, I was on a slope, and I stuck both left wheels in a small washout concealed by vegetation. It allowed the two right hand wheels to just skim the surface. I though about this one for a while, got out, walked around it, thought about getting my truck with winch, and when my heart rate went back to sub-relativistic speeds I got in , engaged 4WD and the diff lock and in low range just barely eased down on the hydrostat while leaning my considerable body weight well over to the high side.
In retrospect I wish three things: 1. It didn't happen, 2. there were hard points on the ROPS cab where you could safely tie ropes to the ROPS. I could have run a line to a tree or a vehicle as a deadman and prevented roll over or a full laydown while "driving" it out., or 3. I would have walked out and brought in another vehicle as a safety measure.
Now you know why I am interested in the ballast issue. I would like a lower CG. I may go for foam fill in the tires since I can't have "ballast" That will give just a little improvement to the CG (and cut out ALL flats, the real motivation for foam) but I want to understand Kubota's implementation and their reasoning before I decide how to supply the ballast. Implements are OK, sort of UNTIL you have a tight manuvering situation then a big brush hog is not helpful.
Ponder, ponder,
Patrick