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platypuswill t1_ja4ydsc wrote

Reply to comment by KaareKanin in ELI5: Why does farming equipment require such low horsepower compared to your average car? by thetravelingsong

u/Dr_Sigmund_Fried is correct and you sort of are too. Cars don't NEED all the horsepower they have, they do need some to get up ramps (think freeway) and such but they could go with a lot less. As far as the original question Dr.SigmundFried is right about the torque to horsepower ratio in farm equipment. and u/mmmmmmBacon12345 nails it with their response and u/PckMan explains the difference in what those two measurements of force actually are. hope you learned something new today, please check for yourself though it's good practice. Learning something new is always a cool thing to do.

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Daelan3 t1_ja5mc9j wrote

The formula hp = torque x rpm applies both at the engine crank and at the wheels. This means the faster the wheels are turning (the faster you're going) the less torque they will have at a given power level.

If the engine is putting 100hp to the wheels, at low speeds that's enough torque to spin them. At highway speeds, the wheel torque is so low that you can barely accelerate. It doesn't matter whether the engine is achieving 100hp with low torque and high rpm or vice versa.

A tractor has a high torque low hp engine because such engines have good fuel economy and reliability, and the large size and heavy weight are not a problem for a tractor. It's not that a tractor needs more torque. A 100hp car engine can get double the torque as a 50hp tractor engine through gearing.

You can put an F1 engine in a fully loaded semi truck, lower the final drive ratio, and it will move it no problem. It just won't good fuel economy or reliability.

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KaareKanin t1_ja6v2a5 wrote

The only thing is, I'm fully aware of this. With his answer Fried validated the initial question, and I still maintain that for normal people using cars normally, they don't require much power at all. They may use it in short bursts because it's there, but I've had rentals with only double digit horsepower figures, and I was never a hindrance to normal flow of traffic.

A tractor probably comes close to using what their engines can output frequently, and if they were to do ploughing a lot faster, power requirements would go up. It's almost all about speed.

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platypuswill t1_ja6xxfr wrote

Yes and speed translation comes down to the difference between the original answer of what's more important for each piece of equipment,. Horsepower or torque? For farm equipment it's torque, for cars horsepower. If it's heavy and you need torque for moving heavy loads slowly but with power. taking a hatchback up a hill and onto the freeway horsepower, there have been some awesome answers so far in the responses that nailed it. This was a great question to ask and I hope a lot of others got their answers as well!

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