Drag Coefficient Calculator

Calculate Cd from coast-down data

Instructions

Data Collection:

  • Find a flat, calm road (no wind, no slope)
  • Coast from ~60 mph to ~20 mph
  • Log time vs speed using GPS/OBD data

CSV Format: Upload a CSV file with two columns: Time (seconds) and Speed (mph)

Physics: The tool analyzes deceleration vs velocity² to calculate drag coefficient (Cd) and rolling resistance coefficient (Crr).

Data Upload

Upload a CSV file with Time (seconds) in first column and Speed (mph) in second column

Vehicle Parameters

Default: 1.225 kg/m³ (sea level)

Horsepower Calculator

Default: 0.32 (typical sedan)

Default: 0.015 (typical road tires)

Range for horsepower calculation