Why are tractors measured in HP instead of torque?

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To my understanding of the two, it makes sense to me that torque would be more important but given that they’re advertised on HP instead, I might be wrong in that understanding and I am unsure why.

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The same reason that electric motors are rated by horse power or kilowatt. They are representing the average amount of work that the motor can produce over a set time period. Torque is variable based on rpm.

Gears work wonders so power is what really matters

You need a certain amount of torque at the wheels to pull a plow, if you don’t have enough then it just doesn’t move, but if you want to pull a plow quickly you need power. Most farming implements create drag that works similar to just normal friction where a small plow might pull back at 500 Newtons regardless of speed.

Power is Torque*RPMs with a scale factor depending on your units, and torque at the wheels to pulling force is a flat scale factor depending on the size of the wheels, the end result is that that speed you can pull a given plow through the dirt scales with the power of the engine regardless of the torque value (assuming your gears can get you enough torque at the wheels). Pulling that little plow along at 2 m/s requires 1 kW of power but 4 m/s requires 2 kW while both speeds only require that the torque at the wheels be enough to provide a 500 Newton forward force