Many car enthusiasts, when choosing a new car or assessing the potential of their “iron horse,” first of all pay attention to horsepower. This has become a kind of marketing standard, but the real “live” dynamics of acceleration and the ability to confidently overtake on the track depend on another, more mundane parameter. Exactly torque determines the force with which the crankshaft rotates and the force is transmitted to the wheels, causing a heavy car to move.
Imagine the situation: you need to tow a heavy trailer or accelerate sharply when overtaking a truck on a country highway. At this moment, power expressed in horsepower fades into the background, giving way to newton meters. Understanding the physics of this process helps not only to choose a car wisely, but also to save engine life by choosing the right gears when driving.
In this article we will look in detail at what it is torque, how it relates to power, why diesel engines feel torqueier, and how torque characteristics affect the day-to-day operation of your vehicle. We will move away from dry formulas and consider the practical application of this knowledge.
Physical entity and units of measurement
From a physics point of view, torque is the product of the force acting on the lever arm. In the context of an internal combustion engine, force is generated by the combustion of the air-fuel mixture in the cylinder, pushing the piston down. This translational motion is transmitted through the connecting rod to the crankshaft crank, turning into a rotational motion. The harder the piston pushes and the longer the crank arm (piston stroke), the greater the torque produced.
The basic unit of measurement in the international SI system is the Newton meter (Nm). In the technical characteristics of cars you can also find other designations, for example, kilogram-force per meter (kgf m), which is often found in the documentation for old equipment or trucks. For translation, it is worth remembering that 1 kgf m is approximately equal to 9.8 Nm. It is this value that shows how effectively the engine can overcome the rolling resistance of the wheels and the inertia of the vehicle's mass.
⚠️ Attention: Never confuse maximum torque with torque available at low rpm. The engine can produce 400 Nm, but only at 4000 rpm, which is practically unavailable in city mode without constant operation in high gears.
It is important to understand that torque is not a constant value for a particular engine. It directly depends on the crankshaft speed (rpm). The graph of torque versus speed is called the external speed characteristic (VSC). The ideal engine is one that produces maximum torque over a wide rpm range, providing smooth traction without the need to constantly change gears.
Why is torque more important than power for a driver?
Power is a derivative of torque and rpm. It shows how much work the engine can perform per unit of time. However, for the driver who just wants to accelerate, it is the moment available “here and now” that is important. High power at high revs is good for the track, but in the city elasticity and traction at the bottom are more important.
Relationship between power and torque
There is a persistent misconception that horsepower and torque are competing characteristics. In fact, they are inextricably linked by a mathematical relationship. Power (in kilowatts or horsepower) is calculated as the product of torque times the angular speed of the shaft. In simple terms, horsepower measures how quickly an engine can use its torque.
If you think of an engine as a person tightening a nut, torque is the force with which it pushes on the wrench, and power is the speed at which it can turn that nut. You can push very hard but slowly (high torque, low power), or you can twist very fast with less force (low torque, high power). To accelerate a car, the combination of both parameters available through the transmission is important.
The transmission (gearbox and main pair) acts as a converter. It allows you to sacrifice the speed of rotation of the wheels for the sake of increasing the force (torque) on them, or vice versa. That is why in first gear a car can move a multi-ton load while developing a minimum speed, and in fifth gear it can drive quickly, but with less traction reserve for sharp acceleration.
- 📉 Low RPM: The torque is usually below the peak, but sufficient for driving in a traffic jam without jerking.
- 📈 Average speed: Here there is a “shelf” of torque, providing better acceleration and elasticity.
- 🚀 High speed: The torque may drop, but the power reaches its maximum, allowing you to reach maximum speed.
Gasoline vs Diesel: battle of characteristics
The eternal debate between fans of gasoline and diesel engines is often based precisely on differences in the torque curve. Diesel engines traditionally considered more high-torque. This is due to the high compression ratio and fuel ignition characteristics, which allows you to obtain impressive pressure in the cylinders even at low speeds. Peak torque in modern turbodiesels is often shifted to the range of 1500–2500 rpm.
Gasoline naturally aspirated engines, on the contrary, require spinning up to 3000–4000 rpm to reach peak values. However, modern technologies such as direct injection and turbocharging (systems TFSI, EcoBoost, TSI), allowed gasoline engines to get significantly closer to diesel engines in terms of traction. Now a gasoline engine can produce 80-90% of its maximum torque from 1500 rpm.
The difference is felt in the driving style. Diesel gives a feeling of “locomotive” traction when the car accelerates with almost no drop in speed. A gasoline turbo engine can be just as spirited, but often has a narrower torque shelf or requires more aggressive operation of the gas pedal to turn on the turbine.
| Parameter | Gasoline turbo | Diesel turbo | Gasoline aspirated |
|---|---|---|---|
| Peak torque (rpm) | 1500 – 4000 | 1700 – 2700 | 3500 – 5000 |
| Character of traction | Sharp, explosive | Smooth, constant | Linear, increasing |
| Elasticity | High | Very high | Average |
When towing a trailer for long periods of time, a diesel engine is often preferable as it runs cooler and operates in a more comfortable rev range under load.
Effect of turbocharging on traction
Installing a turbocharger dramatically changes the engine's torque profile. An atmospheric engine is limited by the amount of air it can suck in per stroke. The turbine forces air into the cylinders, allowing you to burn more fuel and get more energy. The result is a sharp increase in torque in a certain speed range.
However, turbocharged engines have a specific feature - turbojam. This is a failure in traction at low speeds, when the exhaust gas pressure is not yet sufficient to effectively spin the turbine. Modern technologies, such as variable geometry turbines or dual supercharging (biturbo), can almost completely eliminate this effect, creating an even “shelf” of torque.
For the driver, the presence of a turbine means that a small engine displacement can produce torque of a large displacement. For example, a 1.4-liter engine can have 250 Nm, which is comparable to a naturally aspirated 2.5-liter unit. This allows you to create economical but dynamic cars. The main thing is to remember the temperature regime, since high loads at low speeds with active supercharging require high-quality oil and a working cooling system.
⚠️ Attention: Do not attempt to sharply open the throttle at low speeds if the engine is still cold. In turbocharged engines, this can lead to detonation and damage to the piston group due to a sudden surge in pressure.
The role of the transmission in the realization of torque
Engine torque alone is meaningless without a properly selected transmission. The job of the gearbox is to convert the high torque and low speed of the engine shaft into the optimal ratio for the wheels. In first gear, the torque gain is maximum, which allows you to start. In higher gears the torque decreases, but the speed increases.
The most important parameter here is main couple gearbox A “longer” main pair reduces engine speed at cruising speed, saving fuel, but worsens acceleration dynamics. A “short” main pair, on the contrary, makes the car more playful, since the wheels receive more torque, but the engine is forced to operate at higher speeds at the same speed.
☑️ Checking the condition of the transmission
In automatic transmissions and variators (CVT), torque is controlled by software. CVTs, in particular, are able to keep the engine strictly at the point of maximum torque or maximum power, providing theoretically better acceleration. However, many drivers complain about the “rubber grip effect” when the speed hangs and the speed is gained smoothly, which is a feature of the operation of a continuously variable transmission.
Practical implications for the driver
Knowing your vehicle's torque characteristics helps you develop the correct driving style. If you have a diesel or turbo-petrol with an early peak of torque, there is no point in “twisting” the engine to the cut-off. It is more effective to upshift earlier, getting into the zone of maximum effort. This reduces fuel consumption and wear of parts.
When overtaking on the highway, it is important to understand what gear you are in. If you are driving in a high gear (for example, 6th) and need to accelerate quickly, simply using the gas pedal may not work, since the torque at these speeds has already dropped. In such a situation, it is necessary to switch to a lower gear (for example, 4th or 5th) to raise the speed to the peak thrust zone.
The torque is also important when driving off-road or in snow. Here, the ability of the engine to produce force at minimum speed is critically important, so as not to cause the wheels to slip. Engines with high torque at the “bottoms” allow you to move under tension, controlling the adhesion of the wheels to the surface.
Main conclusion: For city driving and overtaking safety, it is more important to have a wide range of torque at medium speeds than maximum power at high speeds.
Frequently asked questions (FAQ)
Is it possible to increase engine torque?
Yes, this is possible in several ways. The most common is chip tuning, which allows you to change the software of the control unit, increasing the boost pressure (for turbo engines) and adjusting the ignition timing. Also, a mechanical increase in volume (boring cylinders) or installing a turbine on an atmospheric engine is guaranteed to increase torque.
Why are electric cars so fast from a stop?
Electric motors have a unique characteristic: they produce maximum torque (100%) from the very first revolutions (0 rpm). They do not need to wait for the speed or pressure to build up, like an internal combustion engine. This provides an immediate and powerful response to the accelerator pedal, creating a "shot" feeling when starting.
Is high torque harmful to the transmission?
An excessively high torque, especially if it significantly exceeds the calculated one for a given gearbox model, can lead to accelerated wear of clutches in automatic transmissions, stretching of chains in CVTs or breakage of gear teeth in mechanics. Therefore, when boosting the engine, strengthening the transmission is often required.
What is “torque shelf”?
This is the engine speed range in which it produces maximum or near maximum torque. The wider this shelf, the more comfortable and flexible the car feels in motion, since the driver less often has to change gears to maintain dynamics.