[JDBrian]

Weight and low gearing on the steam tractor wins! Also, look at the angle of the tow rope. The JD rear end is being lifted up by the pull on the rope reducing traction.

 

[JDBrian]

Understood. My point was that it was never a fair match to start with. Traction is key. Weight and surface area in contact with the ground factor in. It clearly shows the difference in technology used and the different design priorities considered between a modern pulling tractor and a vintage steam traction unit. HP = torque x rpm x K. I think gearing is relevant to pulling loads. If you are not traction limited then the torque at the wheels will be the limit and that depends on available HP at the working RPM and the gear ratio. If you have a lot of traction you can still move a lot of weight with a few HP, you just can’t move it quickly.