Calculator Inputs
Formula Used
Available wheel torque: Wheel Torque = Engine Torque × Gear Ratio × Final Drive Ratio × Efficiency.
Available tractive force: Tractive Force = Wheel Torque ÷ Wheel Radius.
Road demand force: Total Force = Acceleration Force + Grade Force + Rolling Resistance + Aerodynamic Drag.
Acceleration force: F = m × a.
Grade force: F = m × g × sin(θ), where θ = arctan(grade% ÷ 100).
Rolling resistance: F = m × g × cos(θ) × Crr.
Aerodynamic drag: F = 0.5 × ρ × Cd × A × v².
Required wheel torque: Required Torque = Total Force × Wheel Radius.
How to Use This Calculator
- Enter the drivetrain values, including engine torque and ratios.
- Provide wheel radius and number of driven wheels.
- Fill road load inputs such as mass, speed, grade, and drag.
- Submit the form to compare available and required torque.
- Review the margin, force breakdown, and charted torque trend.
- Download the summary as CSV or PDF if needed.
Example Data Table
| Mode | Engine Torque | Gear Ratio | Final Drive | Efficiency % | Wheel Radius m | Output Torque Nm |
|---|---|---|---|---|---|---|
| Powertrain | 250 | 3.5 | 4.1 | 90 | 0.31 | 1027.82 |
| Road Load | 0.31 | |||||
| Powertrain | 320 | 2.1 | 3.9 | 92 | 0.34 | 751.95 |
| Road Load | 0.36 |
Frequently Asked Questions
1. What does wheel torque tell me?
It shows the twisting force delivered at the wheel. This value helps estimate launch strength, climbing ability, and whether the drivetrain can satisfy road load demand.
2. Why is wheel torque higher than engine torque?
Transmission and final drive ratios multiply torque before it reaches the wheel. Efficiency losses reduce some output, but the total can still exceed engine torque significantly.
3. Why does wheel radius matter?
A larger radius reduces tractive force for the same wheel torque. Smaller effective radius increases force at the road surface, which can improve acceleration and climbing response.
4. How does grade affect required torque?
Steeper grades add a gravity component opposing motion. That extra opposing force raises the torque needed at the wheel to maintain speed or accelerate uphill.
5. Is aerodynamic drag important at low speed?
Usually less important at low speed. Drag grows with the square of speed, so it becomes more significant at highway speed and can dominate road load later.
6. What is a good torque margin?
A positive margin means available wheel torque exceeds estimated demand. Larger positive margins improve reserve capacity, while negative margins suggest the setup may struggle.
7. Can I use this for electric vehicles?
Yes. Replace engine torque with motor torque and enter the effective reduction ratio, drivetrain efficiency, and wheel radius. The road load side remains applicable.
8. Does this replace full vehicle simulation?
No. It is a fast engineering estimator. Tire slip, transient traction limits, power limits, shift behavior, and detailed efficiency maps require deeper simulation.