Weight of the Koyker 160 loader with a 5' bucket, and the frame was around 750 lbs. to start with. Add a struck bucket of 3/4" crushed rock and you start to see the front tires squat down. Don't know what the rock weighs, but the total weight of the loader and rock at that point has to be getting close to 1200 lbs. At least with my YM3000 2 wheel drive, the spindles on the front axles weren't much bigger than 1 1/4" in dia. and the weight capacity of the front tires, and the axles, were the weak link. With a 5' landscape rake on the 3 point, weight of the load wasn't a factor keeping the rear wheels on the ground. Don't know what the term " break away " they define in the loader manual means, but I'm sure it's having to do with that 1200 lb. added weight on the loader itself. I wouldn't want to be lifting much more than a full bucket load at least with these small 2 wheel drive tractors. Think the issue with the 4 wheel drive tractors will come down to keeping the tractor from tipping, and the load capacity on the front tires. That's why I set the relief valve on the joystick where it would just lift the front of the tractor off the ground, no more. At that setting it would lift anything reasonable that I had in the bucket and not break the tractor. I sold that tractor after 8 years of hard use and it was still in good condition with nothing broken or bent so that relief valve setting worked out for me over time and didn't abuse the tractor.
Chris