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Drivetrain Loss Calculator

📅Last updated: December 11, 2025
✓Reviewed by: LumoCalculator Team

Calculate drivetrain power loss and convert between engine horsepower (BHP) and wheel horsepower (WHP). Essential for understanding dyno results and real-world performance.

Drivetrain Loss Calculator

BHP ↔ WHP conversion

Calculation Results

🚗
Manual
Rear-Wheel Drive (RWD)
Engine Power (BHP)
300 HP
Wheel Power (WHP)
270 HP
Power Loss
30 HP
Loss Percentage
10.0%
Drivetrain Efficiency
90.0%
Loss Breakdown
Transmission~6%
Differential~4%
💡 Summary

With a Manual transmission and Rear-Wheel Drive (RWD), approximately 10.0% of power is lost through the drivetrain. Your 300 HP engine produces about 270 HP at the wheels.

Formula & Calculation

WHP = BHP × (1 - Loss%)
WHP = 300.0 × 0.900 = 270.0 HP

Power in Different Units

Engine300 HP / 223.7 kW / 304 PS
Wheel270 HP / 201.3 kW / 274 PS

Related Calculators

Typical Drivetrain Losses

SetupLoss RangeExample Vehicles
Manual + FWD8-10%Honda Civic Si
Manual + RWD10-12%Mazda MX-5, BMW M3
Auto + FWD12-15%Toyota Camry
Auto + RWD14-17%Lexus IS350
DCT + RWD10-13%Porsche PDK, BMW M DCT
Manual + AWD15-18%Subaru WRX STI
Auto + AWD18-22%Audi Quattro
CVT + FWD14-18%Nissan Altima
EV Single Speed3-6%Tesla, Porsche Taycan

Understanding BHP vs WHP

🔧 BHP (Brake Horsepower)
  • • Measured at engine crankshaft
  • • Used in manufacturer specs
  • • Measured on engine dyno
  • • Higher number (no losses)
🛞 WHP (Wheel Horsepower)
  • • Measured at the wheels
  • • Shows real-world power
  • • Measured on chassis dyno
  • • Lower due to drivetrain loss

Factors Affecting Drivetrain Loss

Transmission Type

Manual transmissions are most efficient; torque converters in automatics lose power to fluid coupling

Driveshaft Length

RWD vehicles have longer driveshafts with more rotational mass and friction

Number of Differentials

AWD/4WD systems have multiple differentials, each adding friction losses

Transfer Case

AWD transfer cases add complexity and power loss; some have viscous couplings

Fluid Temperature

Cold fluids are thicker, increasing losses; hot dyno sessions show higher WHP

Tire Slip

Dyno roller friction varies; tire pressure and compound affect readings

Transmission Efficiency

✓ Most Efficient
  • • EV Single Speed (~5% loss)
  • • Manual transmission (~8% loss)
  • • DCT/PDK (~9% loss)
✗ Less Efficient
  • • Traditional Auto (~12% loss)
  • • CVT (~14% loss)
  • • AWD systems add +5-7%

Dyno Testing Tips

📊 Before Your Session
  • • Check tire pressure (use same for all runs)
  • • Warm up engine fully
  • • Note ambient temperature/humidity
  • • Use same dyno for comparisons
📈 Interpreting Results
  • • WHP varies 5-10% between dynos
  • • SAE correction normalizes conditions
  • • Compare relative gains, not absolutes
  • • Torque curve shape matters too

Common Misconceptions

❌ "My dyno shows more than factory HP"

Some dynos overread due to calibration or type. Always compare on the same dyno. Factory BHP is measured at the crank; your WHP should be 10-20% lower.

❌ "AWD is slower because of drivetrain loss"

While AWD loses more power, it puts more to the ground through better traction. In launches and wet conditions, AWD often wins despite lower WHP.

❌ "Lighter flywheel adds horsepower"

A lighter flywheel doesn't add HP; it reduces rotational inertia, making the engine rev faster. This improves response but doesn't change peak power.

Frequently Asked Questions

What is drivetrain loss?
Drivetrain loss is the power lost between the engine (crankshaft) and the wheels due to friction and mechanical inefficiencies in the transmission, driveshaft, differential, and other drivetrain components. It's typically measured as a percentage of engine power.
What is the difference between BHP and WHP?
BHP (Brake Horsepower) is the power measured at the engine's crankshaft, typically from manufacturer specifications. WHP (Wheel Horsepower) is the actual power delivered to the wheels, measured on a chassis dynamometer. WHP is always lower than BHP due to drivetrain losses.
How much power is lost through a typical drivetrain?
Drivetrain loss varies by configuration: Manual FWD loses about 8-10%, Manual RWD loses 10-12%, Automatic RWD loses 14-17%, and AWD systems can lose 15-22%. EVs with single-speed transmissions are most efficient at 3-6% loss.
Why does AWD have higher drivetrain loss?
AWD systems have additional components that create friction: a transfer case to split power between axles, an extra differential, and sometimes a viscous coupling or electronic clutch. Each component adds mechanical losses, resulting in 15-22% total drivetrain loss.
Why does my dyno result differ from these calculations?
Dyno results vary based on: dyno type (inertia vs. load-bearing), tire pressure and compound, ambient temperature and humidity, engine temperature, dyno calibration, and wheel size. Results can vary 5-10% between different dynos.
Can I reduce drivetrain loss?
Yes, you can reduce loss by: using lightweight synthetic fluids, installing a lighter flywheel/driveshaft, using a more efficient transmission (manual or DCT), and keeping drivetrain components well-maintained. However, gains are typically small (1-3%).