Tractive Effort Calculator
Calculate the pulling force generated by a vehicle or locomotive.
What is Tractive Effort?
Tractive effort is a measurement of the pulling or pushing force exerted by a vehicle, locomotive, or machine to move a load. In mechanical engineering and railway physics, it represents the force available at the point where the driving wheels meet the surface (the "contact patch").
Unlike horsepower, which measures the rate of doing work, tractive effort measures the raw force. This is critical for determining whether a vehicle can overcome inertia to start moving, climb a specific grade, or tow a specific weight.
The Tractive Effort Formula
For most wheeled vehicles, tractive effort is calculated using the following engineering formula:
- TE: Tractive Effort (Newtons)
- T: Engine or Motor Torque (Newton-meters)
- G: Total Gear Reduction (Transmission Ratio × Final Drive Ratio)
- η: Driveline Efficiency (expressed as a decimal, e.g., 0.90 for 90%)
- R: Radius of the Driving Wheel (Meters)
Real-World Example
Imagine a heavy-duty truck with the following specifications:
- Peak Torque: 800 Nm
- First Gear Ratio: 4.5:1
- Final Drive Ratio: 3.7:1 (Total Ratio = 16.65)
- Driveline Efficiency: 85% (0.85)
- Wheel Radius: 0.45 meters
Using the formula: TE = (800 × 16.65 × 0.85) / 0.45. This results in approximately 25,122 Newtons of force available to start the vehicle in motion.
Factors Influencing Tractive Effort
Several variables impact the actual performance of a vehicle beyond the theoretical calculation:
- Adhesion: The friction between the wheel and the surface. If the tractive effort exceeds the adhesive limit, the wheels will slip.
- Rolling Resistance: The force opposing motion caused by tire deformation and surface friction.
- Aerodynamic Drag: At higher speeds, air resistance significantly reduces the "effective" tractive effort available for acceleration.
- Gradient: Gravity adds a resistive force when climbing hills, requiring higher TE to maintain or increase speed.