Speed to Horsepower Calculator

The Formula

The formula for calculating horsepower from speed is:

\[Horsepower = \frac{(R_r + R_a) \times V}{375}\]

Where:

• R_r: Rolling resistance (lbs) = 0.015 × Weight
• R_a: Air resistance (lbs) = 0.5 × 0.00256 × V² × C_d × A
• V: Vehicle speed (mph)
• C_d: Drag coefficient
• A: Frontal area (sq ft)

Calculation Steps

1. Calculate rolling resistance: R_r = 0.015 × Weight
2. Calculate air resistance: R_a = 0.5 × 0.00256 × V² × C_d × A
3. Sum the resistances: Total Force = R_r + R_a
4. Calculate horsepower: HP = (Total Force × V) ÷ 375

Example Calculation

Let's calculate the horsepower for a vehicle with the following parameters:

• Speed: 60 mph
• Weight: 3500 lbs
• Drag Coefficient: 0.3
• Frontal Area: 22 sq ft

1. R_r = 0.015 × 3500 = 52.5 lbs
2. R_a = 0.5 × 0.00256 × 60² × 0.3 × 22 = 67.74 lbs
3. Total Force = 52.5 + 67.74 = 120.24 lbs
4. HP = (120.24 × 60) ÷ 375 = 19.24 HP

Visual Representation

This visual shows the relationship between speed and horsepower based on our example calculation.