Driveline Torque Calculator

Although your engine may be capable of producing 300 Newton metres of torque, not all the torque is transmitted to the road. There are a series of gears between the engine and the wheels that multiply the rotational motion several times over. This multiplication allows even a modest four-cylinder engine to get a heavy vehicle moving from rest.

The drivetrain torque is the rotational force that acts on the wheels after being transmitted through the transmission and final drive, with a small amount of torque lost due to friction. If you input engine torque, both gear ratios, and drivetrain efficiency, then you will get wheel torque. You can also leave any fields blank for the calculator to solve for those values.

What is the torque of the drivetrain?

The powertrain transmits the torque from the engine to the wheels through a transmission, driveshaft and differential in the final drive. The value of the torque changes at each step before it reaches the road.

The gear ratio of the transmission determines how much engine torque is multiplied in a particular gear. A first gear with a high ratio close to 3.5 to 1 provides maximum multiplication for acceleration, and higher gears reduce this multiplication in favor of higher speed.

The final drive ratio set by the pinion and crown wheel pair in the differential adds an additional constant increase here. The typical final drive ratio of a passenger car is about 3.0 to 1, while for trucks made for towing applications values of 4.10 to 1 or higher can be used.

No transmission is perfectly efficient. Bearings, gear meshing and oil churning all convert some of the torque into heat. As a modern drivetrain in good condition is around 85-95% efficient, between 5-15% of the torque will be lost before it reaches the wheels.

Formula understanding.

The wheel torque amplifies the motor torque through each transmission and corrects for losses due to friction.

In this case T_w is the wheel torque, T_e is the engine torque, G_t is the transmission ratio of the gearbox, G_f is the final drive ratio and η is the efficiency of the drivetrain expressed as a decimal.

Let's take a car that produces 300 Newton meters of torque in first gear. The transmission ratio is 3.5, the final drive ratio is 3.0 and the efficiency is 90 percent. The amplification by the transmission is as follows:

After another amplification by the differential, the overall result is corrected by the efficiency.

The motor's torque is 300 newton meters and it will be boosted to about 2,835 at the wheels, which is almost a tenfold increase. The following table shows the individual symbols and their example values.

From wheel traction to speed.

The wheel torque alone only gives you half the information. When traction control is engaged, the computer divides the wheel torque by the tire's rolling radius to calculate the force that the vehicle is pushing on the ground with. If this force exceeds the tires' maximum grip capacity, then the tire will start slipping. This is why high-torque vehicles tend to spin their wheels easily in low gears.

The same gear set that doubles the torque also divides the wheel speed by the same ratio. If you select "Speed" and enter engine rpm, the calculator will show wheel revolutions per minute (rpm) and estimated road speed. A high gear creates torque for acceleration while a low gear keeps engine rpm down at highway speeds.

What you can do with this calculator:

When upgrading or replacing the engine you can check if the driveshaft, axle shaft and CV joints are capable of handling the new wheel torque to avoid component failure. When selecting a transmission you can see exactly how wheel torque changes when switching from 3.73 to 4.10. When investigating traction you can compare wheel torque with the maximum grip depth that a tire can provide on a particular road surface. Engineers use these same values to determine the size of drivetrain components and ensure a safety margin for peak loads.

Tips for accurate results:

Use the maximum torque value measured by a dynamometer if possible. Published values are ideally measured on the flywheel under optimal conditions. With all-wheel and four-wheel drive, efficiency falls to 82-88 percent due to friction losses through the transfer case and additional driveshafts. Bear in mind that actual wheel torque also depends on temperature, fluid condition and wear.