Every car enthusiast, looking at the technical characteristics of a new or used car, first of all pays attention to the engine power figures. However, experienced mechanics and professional racers know that a completely different parameter is responsible for the acceleration dynamics and the car’s ability to “drag” a load - torque. It is this value that determines how confidently the car will start from a stop, whether it will be able to overtake a truck on the highway or climb a steep hill without shifting to a lower gear.
Understanding the physical essence of this phenomenon and knowing how the rotational force of the shaft is measured is critical for the correct choice of transmission and engine operating mode. Many drivers mistakenly believe that the higher the horsepower, the better the car, ignoring the level of torque. In reality it is Newton meter (Nm) is a unit that describes the traction force available on the wheels at a particular point in time.
In this article, we'll look at why diesel engines often feel more torquey, how power and torque are related, and why low rpms of maximum effort are more important for city driving. You will learn how to correctly read dependency graphs and what to look for when tuning the power unit.
The physical essence of rotating force
Torque is the product of the force acting on the lever arm. In the context of an internal combustion engine, force is the gas pressure pushing the piston, and leverage is the distance from the center of the crankshaft to the connecting rod mounting point. Torque unit in the international SI system - Newton meter (Nm). This means that if a force of one Newton is applied to a lever one meter long, perpendicular to this lever, we will obtain the desired torque of 1 Nm.
It is important to understand the difference between a static force and a dynamic process. An engine can create enormous pressure in the cylinders, but if the crankshaft does not rotate, no useful work is done, despite the presence of torque. Process mechanics is such that the maximum value of this parameter is achieved not at maximum speed, but in a certain range, which engineers try to expand for a comfortable ride.
For clarity, let's imagine that you are trying to unscrew a rusty nut with a wrench. The length of the key is the shoulder, the strength of your arm is the effort. If the key is short, you will have to press very hard. If you put the tube on the wrench, increasing the shoulder, then less manual effort will be required, but the nut will move with the same effect. In the engine crankshaft acts as an axis of rotation, and the connecting rod-piston group transmits the energy of fuel combustion.
⚠️ Attention: Never confuse units of measurement. Pound-foot (lb-ft) is often used in English-language literature. 1 lb-ft is approximately equal to 1.35 Nm. An error in conversion during chip tuning can lead to incorrect settings of fuel maps.
Why is torque important at low revs?
At low speeds, the engine does not have time to fill the cylinders with the optimal amount of mixture, so engineers use variable valve timing systems and turbocharging to create pressure. High torque at the “bottom” allows you not to keep the engine under the stress of high speeds during acceleration.
Newton Meter vs Horsepower
The eternal dispute between car enthusiasts is based on the opposition of these two quantities. Horsepower is a unit of measurement power, that is, the speed of work. Power shows how much energy the engine can produce per unit time. The connection formula is simple: power is equal to the product of torque and shaft speed. Therefore, you can have huge torque at low speeds (like a tractor) and low power, or high torque at high speeds (like a sports car) and huge power.
Let's look at an example. A diesel truck has huge torque but low rev limits. This allows it to pull a multi-ton trailer, but its maximum speed will be limited. A sports motorcycle has less torque, but is capable of spinning up to 15,000 rpm, producing colossal power and high speed. Unit of measurement Nm here shows the “jerk strength”, and horsepower is the “speed ceiling”.
For everyday use in the city, it is the torque characteristics that are more important. When you're at a traffic light and the light turns green, you need to quickly pick up speed. A car with a high torque shelf will accelerate faster without the need to “crank” the engine to the cutoff. It also affects the engine's elasticity—the ability to accelerate from low revs into top gear.
Power determines the maximum speed of the car, and torque determines the dynamics of acceleration and the ability to overcome resistance.
Units of measurement and conversion systems
In the modern world, there are several measurement systems, which often creates confusion when studying technical documentation from different countries. The basic unit of the SI system is the Newton meter. However, imperial units are still widely used in the automotive industry, especially in the US and UK. Also in Russia and the CIS countries, a non-systemic unit was historically used - kilogram-force-meter (kgf m).
To correctly compare the characteristics of cars from different markets, you need to be able to translate values. For example, an American muscle car may have 400 lb-ft of torque, which for a European driver means little without conversion. Knowing the conversion factors helps to objectively evaluate traction characteristics power unit.
Below is a table of basic units of measurement and conversion factors that will help you navigate any specifications:
| Unit of measurement | Designation | Equal to Nm (approximately) | Where is it used? |
|---|---|---|---|
| Newton meter | Nm (Nm) | 1.0 | Europe, Asia, Russia (SI) |
| lb-ft | lb-ft | 1.356 | USA, UK |
| Kilogram-force meter | kgf m | 9.81 | Old tech. USSR documentation |
| Pound-inch | lb-in | 0.113 | Precision mechanics, fasteners |
When working with torque wrenches, it is especially important to respect the units of measurement. If your car manual says to tighten the cylinder head bolts to 100 Nm, and you set the wrench to 100 lb-ft (which is 135 Nm), you can easily strip the threads or break the bolt. Twisting the cylinder head fasteners by 20% above the norm in 90% of cases leads to deformation of the plane of the cylinder head or breakage of the studs.
Effect of motor type on torque curve
The nature of the torque curve is fundamentally different for different types of engines. Gasoline naturally aspirated engines traditionally have a peak-shaped characteristic: the torque increases with speed, reaches a peak in the zone of 4000–6000 rpm and then falls. This requires the driver to change gears frequently to keep the engine in good shape. Atmospheric engine loves speed.
Diesel engines, thanks to their high compression ratio and the use of turbocharging, produce maximum torque already at 1500–2500 rpm. This “shelf” of torque allows you to feel confident in the flow, rarely falling below fourth gear. Turbocharged petrol engines (TFSI, EcoBoost, TSI) have tried to combine the advantages of both worlds, offering high torque over a wide range.
Electric motors have taken the concept of torque to a new level. The electric motor produces 100% of its torque from the very first revolution. The lack of flywheel inertia and the need to gain speed to create pressure make electric cars leaders in launch dynamics. Electric motor thrust available instantly, without delays in spinning up the turbine or opening the throttle.
⚠️ Attention: When chip-tuning diesel engines, do not try to increase the torque at low speeds above the factory values by more than 15%. This can lead to checking the crankshaft liners, since the oil pump at idle speed will not have time to create the required lubricant pressure.
Torque and transmission
The torque produced by the engine passes through the transmission, where it is transformed. The gearbox acts as a torque multiplier. In first gear, which has the highest gear ratio, the engine torque increases several times, allowing you to move the multi-ton mass of the car. However, the speed of rotation of the wheels decreases proportionally.
The final drive and differential also contribute to the overall force pushing the vehicle. That's why SUVs with big wheels often require larger engines or major transmission modifications. Increasing the wheel diameter without changing gear ratios leads to loss of traction, since force application shoulder increases, but the engine torque remains the same.
In automatic transmissions, the torque converter plays an important role. It is capable of multiplying (increasing) torque when starting from a standstill, which makes the launch smoother and more powerful. Variable speed drives (CVTs), in turn, try to keep the engine at the point of maximum efficiency or maximum power, artificially creating the feeling of constant torque.
☑️ Diagnosis of craving problems
Practical implications for the driver
Knowing your vehicle's torque characteristics helps you develop an economical driving style. If you know that your engine's peak torque occurs at 3500 rpm, then for dynamic overtaking it makes sense to switch to a lower gear so that the tachometer needle is in this zone, rather than trying to “push” the gas pedal in fifth gear at 2000 rpm.
This knowledge is also critical when choosing a car for specific tasks. For towing a trailer or driving off-road, the priority is the engine size and the presence of a turbine, providing high torque at low speeds. For track racing, where maximum corner exit speed is important, overall power and the ability of the engine to rev to redline are more important.
When operating a car in mountainous areas, it is the torque reserve that allows you to climb uphill without frequent switching and engine overheating. Trying to force a naturally aspirated small engine to pull uphill in a high gear leads to detonation and destruction of the piston group.
To save fuel in the city, try to keep the speed in the zone of 80-90% of the maximum torque. In this range, the engine burns the mixture most efficiently and produces maximum thrust at minimum consumption.
What is the difference between torque on the flywheel and torque on the wheels?
Flywheel torque is what the engine produces. Wheel torque is the torque on the flywheel multiplied by the gear ratio of the selected gear and the main pair, minus friction losses in the transmission (about 15-20%). It is the moment on the wheels that pushes the car.
Is it possible to increase torque without chip tuning?
Yes, slightly. Installing a zero-resistance intake system, direct-flow exhaust and correct valve timing can add 5-10% of torque, especially at high speeds. However, the main gain comes from reprogramming the ECU.
Why does diesel smoke under load?
Black smoke is unburnt fuel. Diesel engines operate on the principle of mixture formation in the combustion chamber. With a sharp increase in load (gas supply), the turbine has not yet spun up, there is little air, and the nozzle has already supplied a lot of diesel fuel. Some of the fuel does not burn and flies out in the form of soot. This is the price to pay for high torque at low speeds.