One way to think about it is a dual teeter totter... [ even I am not to old too remember those.... ] If you have a loader tractor and have the bucket full of something, that weight is way forward of the front axle which is bearing the entire load. You can put a million tons of weight centered onto the rear axle, and that will not take any of the load off the front axle. It's all on the front teeter totter. But, any weight you add behind the rear axle makes the rear teeter totter try to lift up the front of the tractor and remove a little weight off the front. Since the front load is way in front of the front axle, you actually need a huge weight on the rear to try to make a difference. Adding tire weight helps keep your rear end on the ground and gives you that ' feel good ' experience, but does nothing to help the front axle/bearings/etc... If you are lifting a ton way in front of your front axle, you probably need a ton ballast 15 feet behind your rear on the 3pt to make a real difference... but that would not be very practical. So you have to try to do what you can. When lifting without and tire weight or rear ballast the rear of the tractor's weight is also transferred to the front axle, which really stresses the front axle. Besides loosing rear traction, the tractor rear can violently slam side ways pivoting on the front axle....... [ lot's of fun ]
