Manufacturers quote power at the crankshaft, but a chassis dynamometer measures it at the wheels. Gearbox, driveshaft, differential and wheel bearings each take a small share, so typical losses are 10–15% for front-wheel drive, 15–18% for rear-wheel drive and 20–25% for all-wheel drive.
How to use the Wheel Horsepower Calculator
- Engine (crank) horsepower
- Drivetrain
- Custom drivetrain loss
- Every result field is editable: type into Wheel horsepower and Engine (crank) horsepower plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the engine horsepower and pick the drivetrain (or enter your own loss). Type a dyno reading into the result to find the crank horsepower.
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| Engine (crank) horsepower | In hp |
| Drivetrain | Choose one: Front-wheel drive, manual (≈ 12%), Front-wheel drive, automatic (≈ 15%), Rear-wheel drive, manual (≈ 15%), Rear-wheel drive, automatic (≈ 18%) … |
| Custom drivetrain loss | In % |
What each result means
- Power lost in the drivetrain = [Engine (crank) horsepower] – [Wheel horsepower]
- Wheel power in kW = [Wheel horsepower]×0.74569987158227
Example values
How the main result changes when Engine changes and everything else stays at the example values above:
| Engine (crank) horsepower (hp) | Wheel horsepower (whp) |
|---|---|
| 150 | 128 |
| 225 | 191 |
| 300 | 255 |
| 375 | 319 |
| 450 | 383 |
| 600 | 510 |
Formula
Wheel hp = engine hp × (1 − drivetrain loss)Engine hp = wheel hp ÷ (1 − loss)Worked example
Inputs — Engine (crank) horsepower: 300 hp; Drivetrain: Rear-wheel drive, manual (≈ 15%); Custom drivetrain loss: 17 %.
Results — Wheel horsepower = 255 whp; Power lost in the drivetrain = 45 hp; Wheel power in kW = 190 kW.
Frequently asked questions
How much power is lost through the drivetrain?
Roughly 10–15% for front-wheel drive, 15–18% for rear-wheel drive and 20–25% for all-wheel drive.
Why do different dynos read differently?
Dyno type, correction factors, tyre pressure and temperature all affect the reading; compare runs on the same dyno.
Is the loss a fixed percentage?
Not exactly – part of it is fixed friction, so the percentage is lower on high-power cars.
What formula does the Wheel Horsepower Calculator use?
Wheel hp = engine hp × (1 − drivetrain loss).