IT all comes down to thew center of gravity, and where your weight gets focused. ON ztr's and riders you are sitting 2-3' up in the air while a stander or walk behind with a sulky your standing 6" or less from the ground. This makes your weight free and not as locked to the seat up high pulling the tractor over. I hate mowing hills with any kind of machine. I had a 48" walk behind slide 20 ft down a hill before I got it shut down.