Crank To Wheel HP Calculator

What Is Crank Horsepower (BHP)?

Crank horsepower (BHP) is the power measured at the engine’s crankshaft before it goes through the transmission, driveshaft, differential, and wheels.

It is measured on an engine dyno, where the engine runs outside the vehicle.

Key points:

• Also called brake horsepower (BHP)
• Measured without drivetrain loss
• Often used by manufacturers in marketing
• Usually higher than wheel horsepower

If a car is rated at 300 HP by the factory, that number usually refers to crank horsepower.

What Is Wheel Horsepower (WHP)?

Wheel horsepower (WHP) is the power measured at the wheels using a chassis dyno.

This is the power that actually moves the car forward.

Key points:

• Measured at the tires
• Includes drivetrain losses
• Always lower than crank horsepower
• Gives a more realistic performance number

If your car makes 260 WHP on a dyno, that means 260 horsepower is reaching the ground.

What Is Drivetrain Loss?

Drivetrain loss is the power lost between the engine and the wheels.

Power is absorbed by:

• Transmission gears
• Driveshaft
• Differential
• Transfer case (AWD / 4WD)
• Bearings and friction

This loss is called parasitic loss.

Typical drivetrain loss percentages:

Transmission type also affects loss:

• Manual: lowest loss
• Dual-clutch: +2%
• Automatic (torque converter): +5%

The calculator combines drive type loss and transmission loss to get total drivetrain loss.

Crank to Wheel HP Formula

The calculator uses two main formulas.

1. Convert Crank HP (BHP) to Wheel HP (WHP)

WHP = BHP × (1 − Total Loss Percentage)

Example:

• 300 BHP
• 15% drivetrain loss

WHP = 300 × (1 − 0.15)
WHP = 300 × 0.85
WHP = 255 WHP

So a 300 HP RWD car typically makes about 255 WHP.

2. Convert Wheel HP (WHP) to Crank HP (BHP)

To reverse the calculation:

BHP = WHP ÷ (1 − Total Loss Percentage)

Important:
You do NOT multiply by (1 + loss). That is mathematically incorrect.

Example:

• 255 WHP
• 15% loss

BHP = 255 ÷ 0.85
BHP = 300 HP

This gives you the theoretical crank horsepower.

How the Crank To Wheel HP Calculator Works

The calculator includes:

1. Calculation Mode

You choose:

• Crank (BHP) → Wheel (WHP)
• Wheel (WHP) → Crank (BHP)

2. Horsepower Input

You enter the known horsepower value.

3. Drivetrain Configuration

You select:

• Drive type (FWD, RWD, AWD, 4WD)
• Transmission type (Manual, DCT, Automatic)

The calculator then:

• Adds drivetrain loss percentages
• Applies the correct formula
• Shows WHP or BHP
• Displays parasitic loss
• Shows efficiency percentage
• Converts result into kilowatts (kW)

It also visualizes:

• Power delivered to wheels
• Power lost to drivetrain

This makes it easier to understand where the energy goes.

What Is Efficiency?

Efficiency tells you how much engine power actually reaches the wheels.

Formula:

Efficiency = (WHP ÷ BHP) × 100

Example:

• 255 WHP
• 300 BHP

Efficiency = 255 ÷ 300 × 100
Efficiency = 85%

So 85% of engine power reaches the road.

Real-World Example

Let’s say you dyno your AWD automatic car and get:

• 320 WHP
• AWD loss: 20%
• Automatic transmission: 5%

Total loss = 25%

Now calculate crank horsepower:

BHP = 320 ÷ (1 − 0.25)
BHP = 320 ÷ 0.75
BHP = 426 HP

That means your engine likely produces around 426 crank horsepower.

Why This Calculator Matters

Understanding crank vs wheel horsepower helps you:

• Compare dyno results to factory ratings
• Estimate true engine output
• Evaluate tuning upgrades
• Understand drivetrain efficiency
• Avoid incorrect math when reversing percentages

Many people wrongly assume you just add 15% back. That leads to incorrect numbers.

This calculator uses the correct reverse percentage formula.

When Results May Vary

Keep in mind:

• Dyno types vary (Dynojet, Mustang, etc.)
• Tire size and pressure affect readings
• Weather conditions matter
• Gear used during dyno pull changes results

So results are estimates, not absolute guarantees.

Still, the calculator gives a reliable theoretical conversion.

Crank HP vs Wheel HP: Quick Summary

Drivetrain loss explains the difference.