I did not make my point very clear, sorry.Jeeeeez people........
The weight of the wheel/tire is not an active lever working against the axle. The axle rides the wheel, not the wheel to the axle.
Take two heavy duty saw horses and a 16' 2"x6". Place the saw horses close together and put the 16' 2"x6"on top of them. Now get on top of the 2x6 between the saw horses and jump up and down. I bet that the 2x6 will not break. Now move the saw horses to within 1' of the ends of the 2x6. Now get on the 2x6 in the middle and jump up and down and see if it breaks. My money is on it breaking.
Now how does this apply. the saw horses represent the tires, the 2x6 the axle, you represent the weight of the tractor, and anything attached or suspended from it (3pt implement). When the tractor is not moving this is not a problem. When you are working the tractor, the implement is lowered - no real problem. When you are moving from one place to another is when the implement is going to be suspended from the tractor and your ground speed will be the fastest. Now hit a hole, rock, stump whatever and what happens? A large shock load is placed on the axle and housing. The further out the tires are the larger the shock load in the center will be.
I friend of mine "had" an employee do over $15,000 damage to one of his tractors just this way. The employe changed the tire configuration around for more stability and added spacers. Broke the axle and housing right off the tractor.
There is more to the story but hopefully you get my point.