Calculators · Tyres and gearing
Wheel torque, tractive force and drivetrain loss calculator
What actually moves a vehicle is the force its tyres push against the road. It comes from engine torque multiplied through the gears, less drivetrain losses, divided by the tyre’s rolling radius — and it can never exceed the grip the tyres have. These calculators give tractive force and the acceleration it could produce, the traction limit of the driven wheels, and the drivetrain loss between crank and wheel power.
Tractive force and acceleration potential
Converts engine torque into the pushing force at the tyres in the selected gear, and the acceleration that force could give the vehicle. It ignores air and rolling resistance and assumes the tyres do not spin.
F = T × ratio × η / r a = F / m
Traction limit of the driven wheels
The most force the tyres can transmit is the weight on the driven axle multiplied by the friction coefficient of the surface. If the tractive force above is higher, the wheels spin instead of accelerating harder.
F_max = m_axle × g × μ
Drivetrain loss from crank and wheel power
Compares the engine’s crank power with power measured at the wheels on a chassis dynamometer to find the drivetrain loss. Manual front-drive cars typically lose 10–15%; four-wheel drive and older automatics lose more.
loss = (crank − wheel) / crank
Estimated crank power from a wheel dyno figure
Estimates crank power from a chassis dyno reading and an assumed drivetrain loss. Because the loss is an assumption, treat the result as an estimate rather than a measurement.
crank = wheel / (1 − loss)
Worked example: launching a front-drive car
- 300 Nm through a 13.65 overall first-gear ratio at 90% efficiency gives 3,686 Nm at the wheels.
- Divided by a 0.3075 m loaded radius: about 11,985 N of tractive force.
- With 800 kg on the front axle and μ = 0.8, grip is only 6,276 N — the wheels would spin.
- A car making 170 kW at the wheels with 15% drivetrain loss has about 200 kW at the crank.
Typical drivetrain losses
| Drivetrain | Typical loss |
|---|---|
| Manual, front-wheel drive | about 10 – 15% |
| Manual, rear-wheel drive | about 12 – 17% |
| Modern automatic | about 13 – 20% |
| All-wheel drive | about 18 – 25% |
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About these results
Results are theoretical estimates from standard engineering formulas. Real-world figures depend on conditions these formulas do not capture. Always follow the manufacturer's specifications for maintenance, loading and safety decisions.
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