Calculate wheel torque per driven wheel from engine torque, gear ratio, final drive, efficiency, and driven wheels. Add tire diameter to estimate tractive force at the ground.
Wheel torque calculator computes the actual mechanical torque delivered to a vehicle's driven wheels. By applying formulas for transmission gear multiplication ($R_{gear}$), final drive ratios ($R_{final}$), and parasitic drivetrain losses ($L$), it reveals exactly how base engine torque ($T_{engine}$) is transformed before reaching the hub. It is engineered for automotive builders, drag racers, and tuning enthusiasts evaluating transmission swaps, differential changes, or axle load limits.
Calculating Delivered Wheel Torque
The calculation path isolates the torque multiplier effect of the vehicle's gearing from the frictional losses of the driveline components. The total actual axle torque is calculated using the following primary equation:$$T_{axle} = T_{engine} \times R_{gear} \times R_{final} \times \left(1 - \frac{L}{100}\right)$$
Gearing Multiplier and Theoretical Output
Before friction is applied, the base engine torque is multiplied by the transmission and differential ratios.$$T_{axle\_theo} = T_{engine} \times R_{gear} \times R_{final}$$
Where $T_{engine}$ is the input engine torque, $R_{gear}$ is the selected transmission gear ratio, and $R_{final}$ is the final drive (ring and pinion) ratio.
Parasitic Loss Application
No drivetrain is perfectly efficient. The theoretical output is reduced by the mechanical loss percentage ($L$) occurring through the gearbox, driveshaft, and axles.$$T_{lost} = T_{axle\_theo} - \left(T_{axle\_theo} \times \frac{100 - L}{100}\right)$$
Per-Wheel Distribution
The final true torque applied to the pavement is divided by the number of drive wheels.$$T_{wheel} = \frac{T_{axle\_theo} - T_{lost}}{N_{wheels}}$$
Where $N_{wheels}$ is the user-defined number of driven wheels (typically 2 for FWD/RWD architectures or 4 for AWD/4WD systems).
Required Powertrain Variables
- Engine Torque: The peak or specific-RPM torque output of the engine. This value must be greater than zero.
- Transmission Gear Ratio: The specific ratio of the gear being evaluated. Ratios $>1.0$ (underdrive) multiply torque for acceleration, $1.0$ is direct drive, and $<1.0$ (overdrive) reduce torque for highway cruising. Must be greater than zero.
- Final Drive Ratio: The differential or axle ratio. Must be strictly greater than zero.
- Drivetrain Loss: Parasitic friction loss. Front-wheel drive systems typically experience $10\%$ to $15\%$ loss, rear-wheel drive $15\%$ to $20\%$, and all-wheel drive $20\%$ to $25\%$. The calculator requires a value between $0$ and $99.9$.
- Driven Wheels: The integer divisor for distributing final axle torque.
Metric and Imperial Conversions
The calculator simultaneously processes outputs in both Newton-meters (Nm) and pound-feet (lb-ft). Depending on the input unit selected, it applies standard international conversion factors to generate secondary reference values.
Converting Pound-feet to Newton-meters: $$T_{Nm} = T_{lb-ft} \times 1.3558179$$
Converting Newton-meters to Pound-feet: $$T_{lb-ft} = T_{Nm} \times 0.7375621$$
Mathematical Assumptions and System Limitations
- Rotational Hub Limit: The tool computes rotational torque strictly at the wheel hub. It does not calculate linear tractive force or vehicle thrust, which requires factoring in the loaded rolling radius of the tire.
- Static Friction Modeling: Drivetrain efficiency is calculated as a static linear percentage. In real-world physics, parasitic loss consists of both a fixed inertial loss (which remains constant regardless of engine load) and a variable dynamic frictional loss.
- Symmetrical Torque Split: The distribution math assumes a perfectly locked or evenly split differential, dividing torque equally by the exact integer of $N_{wheels}$. It cannot account for limited-slip or torque-vectoring differentials that bias power unevenly side-to-side or front-to-rear based on grip limits.
Technical Troubleshooting
Why does my overdrive gear yield less total wheel torque than the base engine output?
Does chassis dyno "Wheel Torque" match the output of this calculator?
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