Crank vs. Wheel Horsepower
04/10/2019 10:16 am
We get a lot of questions related to this topic, so we figured a little education wouldn't hurt.
First, let's talk about what horsepower is. Horsepower is a unit of measurement of power, or the rate at which work is done. The term was adopted in the late 18th century by engineers to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.
What is torque? Torque, moment, or moment of force is the rotational equivalent of linear force. The concept originated with the studies of Archimedes on the usage of levers. Just as a linear force is a push or a pull, a torque can be thought of as a twist to an object. Torque is the rush or the pull that you feel in your gut when you put the pedal to the floor.
Crank horsepower and crank torque is the power the engine is generating before any driveline loss is factored in. For example: transmission drag, driveline drag, wheel and tire rotational drag. Crank horsepower is usually measured with the motor pulled out of the vehicle and strapped to an engine dyno.
Wheel horsepower and wheel torque is the truest display of the power output your vehicle is making, due to all the drivetrain loss being factored into the reading. This is important because you could have the same motor in two different vehicles with two different power readouts. On Wranglers and other 4x4 vehicles with large tires, transfer case, solid axles, this loss can be as high as 25-30% from crank horsepower! Wheel horsepower can only be measured on a vehicle dyno.