What Is Wheel Torque?
Your engine produces torque — a twisting force at the crankshaft. But the crankshaft is not where the rubber meets the road. Before that twisting force ever reaches your tires, it passes through the transmission and the final drive, gets multiplied by their gear ratios, and loses some of itself to friction along the way.
Wheel torque is the result: the actual turning force available at the driven wheels. It is the number that decides how hard your car accelerates, how well it climbs hills, and how much weight it can pull. Two cars with identical engines can feel completely different if their gearing turns the same engine torque into very different wheel torque.
The Wheel Torque Formula
[
\text{Wheel Torque} = \text{Engine Torque} \times \text{Gear Ratio} \times \text{Final Drive Ratio} \times \text{Drivetrain Efficiency}
]
Where:
- Engine Torque is the crankshaft output, measured in Newton-meters (Nm) or pound-feet (lb-ft).
- Gear Ratio is the transmission ratio for the gear you are in (for example, 2.5 for a typical second gear).
- Final Drive Ratio is the differential's reduction, commonly between 3.0 and 4.5.
- Drivetrain Efficiency captures friction losses, expressed as a decimal below 1.
Notice two competing effects: the gear ratios multiply the torque up dramatically, while drivetrain efficiency shaves roughly 10–20% off. Because ratios and efficiency are dimensionless, the result comes out in whatever unit you started with.
Typical Drivetrain Efficiency
| Drivetrain | Efficiency | Friction loss |
|---|---|---|
| Front wheel drive (FWD) | 0.90 | ~10% |
| Rear wheel drive (RWD) | 0.85 | ~15% |
| All wheel drive (AWD) | 0.80 | ~20% |
All wheel drive is least efficient because extra differentials and a center driveshaft add more spinning parts, and every spinning part wastes a little energy as heat.
Worked Example: Second Gear, Rear-Wheel Drive
Suppose a sports car makes 400 Nm of engine torque and is pulling in second gear with a ratio of 2.5, a final drive of 4.0, and a rear-wheel-drive layout (efficiency 0.85):
[
\text{Wheel Torque} = 400 \times 2.5 \times 4.0 \times 0.85
]
Step through it:
[
400 \times 2.5 = 1000 \quad\rightarrow\quad 1000 \times 4.0 = 4000 \quad\rightarrow\quad 4000 \times 0.85 = 3400
]
So the wheels see about 3400 Nm — more than eight times the engine's rating, despite losing 15% to the drivetrain. That multiplication is why a car feels urgent in second gear and relaxed in sixth, using the very same engine.
Interpreting the Result
- Low gear, huge wheel torque: tall numerical ratios multiply torque hardest — ideal for launch and climbing.
- High gear, modest wheel torque: overdrive gears (ratios below 1) reduce wheel torque but let the engine cruise at low rpm for economy.
- Comparing cars: matching engine torque means little without gearing. A car with shorter gearing can out-accelerate a stronger engine.
- Dyno context: chassis dynos measure at the wheels, so their figures already include these drivetrain losses — expect roughly 10–20% less than the manufacturer's crankshaft rating.
If you want to dig into the other side of the equation — how much power the gears themselves cost you — try the drivetrain loss calculator.