Crank horsepower vs wheel horsepower: what’s the difference?

You see it all the time.

“This car makes 300 horsepower.”

Cool. But where? At the crank, or at the wheels?

Because here’s the thing. Those two numbers are not the same. And unless you know which one you're talking about, you're either overselling your build or massively underselling it.

This guide breaks down the difference between crank and wheel horsepower, how drivetrain loss works, and why your dyno numbers never match the spec sheet. When you’re done, hit the drivetrain horsepower loss guestimator to run your own numbers and find out how much power your car is actually putting down.

What is crank horsepower?

Also called flywheel horsepower, this is the power measured directly at the engine, before it touches the clutch, gearbox, driveshafts or differentials.

It’s what manufacturers quote in brochures and on spec sheets. It’s measured in a controlled environment, usually with the engine on a bench dyno.

No drivetrain drag

No tyre slip

No real-world friction

Not what your car puts to the ground

What is wheel horsepower?

This is the power measured at the driven wheels using a chassis dyno like a Dynojet or Mustang.

It’s what your car actually delivers to the road after the engine’s power has travelled through the entire drivetrain.

Real-world measurement

Affected by gearbox, tyres, diff, and even oil

Always lower than crank horsepower

Varies based on dyno type and setup

If your 300 horsepower car reads 250 on a dyno, that’s normal. That missing 50 horsepower didn’t vanish. It was lost in the drivetrain.

What is drivetrain loss?

As power travels from the engine to the wheels, some of it gets eaten up by:

• Friction in gears and bearings

• Rotational weight in shafts and axles

• Heat inside the transmission and differentials

That’s drivetrain loss. Here’s what you can expect on average:

So if your engine makes 300 horsepower:

• A FWD car might deliver 255 to 270 horsepower to the wheels

• A RWD car might deliver 240 to 265

• An AWD setup could put down just 225 to 240

These are rough figures. For more accurate guestimations, run your setup through the guestimator.

Why do dyno numbers look low?

You run your car on a dyno. It says 210 horsepower. The factory spec said 260. What gives?

Here's why.

• The manufacturer measured 260 at the crank

• Your dyno shows power at the wheels

• Drivetrain loss is doing its job, as always

The dyno you used, also plays a part. Mustang dynos tend to read lower than Dynojets. Some dynos use correction factors. Others don’t.

The bottom line

If you're comparing dyno runs, tuning your build, or just trying to understand what your car really puts down, you need to know the difference.

• Crank horsepower is what the engine makes

• Wheel horsepower is what your tyres deliver

• Drivetrain loss is the invisible thief in the middle