Fordsons rearing up

[Alan Riach]

The cause of rearing up in any tractors is to do with the position of the drawbar above the ground (strictly speaking above the point where the tire contacts the ground) and nothing to do with its position relative to the axle.
The two points of application of force on the tractor are 1. where the wheel touches the ground (it is nothing to do with the position of the axle) and 2 the point where the load is applied to the drawbar. These two forces apply a turning (or rearing) moment on the tractor. If the drawbar is kept close to the ground the rearing moment is kept low. When 3 point linkage tractors appeared one of the really dangerous tricks was to attach a chain to the top link attachment when pulling out tree stumps etc.(very high drawbar -very high rearing moment - very quick overturning). However Harry Ferguson's 3 point linkage system was the greatest advance in preventing rear turn over accidents that could be made
The confusion of thinking that the position of the axle effects the rearing moment is long held. Imagine the mechanical rotating parts are all welded solid and a magical force is applied where the tire contacts the ground to get the true story. Maybe thinking of a crawler helps - force is applied to tractor where the tracks contact the ground. Of course the force has to get into the tractor frame via the axle bearings but it is the point where the world contacts the tractor (at the ground (and at the drawbar) that is important.

 

[Fixingfarmer]

I do find this interesting and the front hitch support for the drawbar on many John Deere tractors uses this same point on the load shaft down below as the 3 point arms attach. There’s a small pin farther ahead to balance the hitch but as far as the weight being pulled it is in the same spot down low. If you were 10 foot back down low still wouldn’t help much as there would be leverage if you had the weight applied pushing down on the hitch but if it was 10 foot back it also wouldn’t have far to tip before it hits the ground. And if there was a load being PULLED it would make no difference. It would be like if you moved a chisel location on your tool bar one beam ahead. Doesn’t make it pull any easier.

 

[Bob N.Y.]

The cause of rearing up in any tractors is to do with the position of the drawbar above the ground (strictly speaking above the point where the tire contacts the ground) and nothing to do with its position relative to the axle.
The two points of application of force on the tractor are 1. where the wheel touches the ground (it is nothing to do with the position of the axle) and 2 the point where the load is applied to the drawbar. These two forces apply a turning (or rearing) moment on the tractor. If the drawbar is kept close to the ground the rearing moment is kept low. When 3 point linkage tractors appeared one of the really dangerous tricks was to attach a chain to the top link attachment when pulling out tree stumps etc.(very high drawbar -very high rearing moment - very quick overturning). However Harry Ferguson's 3 point linkage system was the greatest advance in preventing rear turn over accidents that could be made
The confusion of thinking that the position of the axle effects the rearing moment is long held. Imagine the mechanical rotating parts are all welded solid and a magical force is applied where the tire contacts the ground to get the true story. Maybe thinking of a crawler helps - force is applied to tractor where the tracks contact the ground. Of course the force has to get into the tractor frame via the axle bearings but it is the point where the world contacts the tractor (at the ground (and at the drawbar) that is important.

I completely disagree with your reasoning. The rear axle of the tractor acts as a fulcrum. Hitching a load below the rear axle increases the downward force on the front of the tractor. Hitching a load above the rear axle creates a lifting force on the front end as the back wheels attempt to "walk out from under" the load. This was more pronounced with the Fordson because of the worm drive differential with the worm below the crown wheel which effectively lowers the fulcrum to that point. Some of the Fordson prototypes had the worm on top of the crown wheel, but that generated too much heat directly under the seat.