What is horsepower and torque and how do they relate to a car being fast or a truck having a towing capacity?
In: Engineering
Horsepower is a measure of the work that can be done in a unit of time.
Torque is a measure of the amount of force that can be applied at a given RPM.
For cars and trucks, more horsepower correlated to a greater amount of work being done over time, so in either situation horsepower would be the measure of productivity of that vehicle.
The formula for Horsepower is
HP = (Torque x RPM)/5252
So say a truck produces 300hp at 4000RPM. A car might produce 300hp at 7000RPM. The car’s engine will be producing less torque than the truck, but both are able to produce the same amount of power.
Torque in this situation determines at what RPM an engine must run to produce a certain power output.
For towing this becomes important because typically the higher you rev an engine, the more energy is lost to heat due to friction. So an engine that can produce a lot of torque at a low RPM will be more efficient and more reliable than an engine that produces less torque at a high RPM.
So if low RPM high torque is more efficient, why do cars use small engines that produce less torque and rev higher? Well it comes down to weight! A car is focused on keeping weight low while having the most possible power output. A truck is focused on maintaining the most efficient operation while still being useful.
The acceleration of a vehicle at low speeds comes down to its power to weight ratio and available traction. So a car will accelerate quicker if it is light and can produce a high power output.
Trucks are less focused about fast acceleration and trade weight for reliable efficient engines that can do lots of work for an extended period of time.
It’s also worth noting that a trucks towing capacity is more a measure of the quality of its suspension, drivetrain, gearing, and ability to slow down a heavy load. Not so much it’s power output. A truck with only 5 horsepower could tow a 50,000 pound load, it would just take a very long time to get anywhere!
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