And that farm tractor may spend much of its working life in huge, established fields. Not the woods, or crossing creeks, or running over logs, or clinging to the side of a hillside. With no suspension to speak of, the terrain is usually the problem, not so much the tractor.
My last four tractors have all been less than 25 HP, for exactly what Sparkplug is saying. My present "utility" tractor is 23 HP, but very very heavy, and with a very low center of gravity. The entire drive train, including the axles, are cast iron. I've got the rear wheels filled. It is 4WD, and runs with a 3-cylinder Mitsubishi diesel engine that has remained unchanged in design for at least 20 years -- and is still being used in many small category-1 utility tractors. When I bought my present tractor about 6-7 years ago, that engine model had been 20 HP for many years. Somewhere in the last 3-5 years California mandated that it should be 23 HP to meet their pollution regulations.
This little tractor weighs in at nearly 3000 lbs., with the front-end loader, which I never remove. Add an implement to the back, like the mating frame-mount backhoe, and it goes up to about 4500-5000 lbs.
No, it doesn't have any suspension, but it moves through the woods, and around my ponds very gracefully. For someone who needs a "utility" tractor, the small 4WD diesels (under 30-35 HP) sure are tough and versatile. Cabs are even available for most of them. Mine has moved incredible amounts of snow, pushed over one heck of a lot of trees, and so many other things I can't even begin to list them. Without any suspension, they don't do well on long trips, plus they only have a maximum road speed of about 10-15 mph. But, they sure will do a lot of work, with minimal maintenance, such as oil changes, regular greasing, filter changing, etc.
