Tractive Force Calculator
Find the push a tire puts on the road. Use the calculator below. Results update as you type.
How the Tractive Force Calculator Works
This calculator works by multiplying engine torque by the gear ratios and efficiency, then dividing by the tire radius. The result is the pushing force at the contact patch.
- Enter the engine torque, for example 400 lb-ft (542 Nm).
- Enter the gear ratio (4.17), axle ratio (3.73) and efficiency (85%).
- Enter the tire height, for example 33 in (838 mm).
- Read the tractive force: 3,846 lbf (17,107 N).
The Formula
The formula is Tractive Force = (Engine Torque × Gear Ratio × Axle Ratio × Efficiency) ÷ Tire Radius.
Wheel Torque = Engine Torque × Gear × Axle × Efficiency Tractive Force (lbf) = Wheel Torque (lb-ft) ÷ (Radius (in) ÷ 12) Tractive Force (N) = Wheel Torque (Nm) ÷ Radius (m)Worked example: 500 lb-ft × 4.17 × 3.73 × 0.85 = 6,610 lb-ft at the wheels. On a 31 in tire (radius 1.292 ft), force = 5,118 lbf (22,765 N).
Conversion Table
The conversion table shows tractive force in 1st gear for 6 engine torque values on 4 tire diameters. A 35 in tire gives 17% less force than a 29 in tire at the same torque.
Multiply any lbf value by 4.448 to get newtons. The force shown is available force; tire grip limits how much reaches the ground.
| Engine Torque (lb-ft) | Engine Torque (Nm) | Wheel Torque (lb-ft) | 29 in Tire | 31 in Tire | 33 in Tire | 35 in Tire |
|---|---|---|---|---|---|---|
| 300 | 407 | 3,966 | 3,282 | 3,071 | 2,885 | 2,720 |
| 400 | 542 | 5,288 | 4,377 | 4,094 | 3,846 | 3,626 |
| 500 | 678 | 6,610 | 5,471 | 5,118 | 4,808 | 4,533 |
| 700 | 949 | 9,255 | 7,659 | 7,165 | 6,731 | 6,346 |
| 1000 | 1,356 | 13,221 | 10,942 | 10,236 | 9,615 | 9,066 |
| 1500 | 2,034 | 19,831 | 16,412 | 15,353 | 14,423 | 13,599 |
Multiply lbf by 4.448 for newtons (N).
What Is the Tractive Force Calculator?
The Tractive Force Calculator is a tool that converts engine torque and gearing into pushing force at the tire contact patch. Tractive force decides acceleration, towing launch and climbing ability.
Tire radius is the lever arm. A larger radius lowers the force at the same wheel torque, which is why larger tires feel slower without a re-gear.
Common Uses
This calculator has 4 uses: towing checks, climbing checks, re-gear payoff and drivetrain comparison.
- Check towing: Compare force with trailer weight.
- Check climbing: Estimate force on steep grades.
- Measure re-gear payoff: Compare force before and after.
- Compare drivetrains: Test engines and gearsets on one tire.