Many motorists when choosing a new or used car pay attention exclusively to the engine power, expressed in horsepower, considering this parameter the only indicator of the "coolness" of the car. However, experienced mechanics and engineers know that the real ability of the machine to move from a place, overcome climbs and overtake trucks on the track meets another, more important parameter – torque. It is this physical quantity that determines how quickly the engine can spin the crankshaft and transfer the force to the wheels.
Understanding what torque is needed for allows not only to correctly choose the car for your needs, but also to significantly extend the transmission life. If power is how much energy a motor can give out per unit of time, then moment is the force with which it does it right now. Without enough thrust, even the most powerful sports car will feel insecure on steep slopes or when the cabin is fully loaded.
In this article, we will examine in detail the physics of the process, compare the performance of gasoline and diesel units, and also find out how transmission gear ratios help convert revs into a useful effort. You will learn to read performance charts and understand why sometimes 200 Nm at low rpm is better than 400 Nm at high rpm.
Physical essence and units of measurement
From a physics perspective, torque It is a product of force on the shoulder of the lever to which it is applied. In the internal combustion engine, the role of the lever is played by the crankshaft crank, and the force is created by the pressure of gases burning in the cylinder, pushing the piston down. The higher the pressure and the longer the stroke of the piston, the greater the force is transferred to the shaft, causing it to rotate.
In the International System of Units (SI), this parameter is measured in Newton meters (Nm). However, in the automotive industry, you can still find old designations, such as the kilogram-force-meter (kgf·m). For conversion, it is enough to know that 1 kgf·m is approximately equal to 9.8 Nm. It is important not to confuse the moment with work, as work is done only when the shaft is really rotating and overcomes resistance.
The key characteristic is not just the maximum value of the moment, but the range of revolutions in which it is available. The engine can produce a peak of 300 Nm, but only at 5000 rpm, which is practically not used in urban traffic. Much more valuable for the driver is the elasticity of the motor - the ability to give 80-90% maximum in a wide range from 2000 to 5000 rpm.
⚠️ Note: When comparing engines of different cars, never look only at the passport power data. Two 2.0-liter engines can have the same power, but completely different torque and moment shelf, which will radically change the experience of driving.
To better understand the physics of the process, it is worth considering how exactly the pressure force is converted into rotation. In diesel engines, the compression ratio is higher, which provides more powerful pressure on the piston at the time of ignition of the fuel. That is why diesel engines traditionally have higher torque at low revs compared to gasoline analogues.
Remember that the torque on the wheels is always higher than on the engine, thanks to the transmission, which works as a lever, multiplying the rotational force at the expense of speed.
Impact of the moment on acceleration and dynamics
The dynamics of acceleration of the car directly depends on how effectively the torque overcomes the inertia of the mass of the machine and air resistance. There is a common misconception that only power accelerates a car, but this is only partly true: power determines the maximum speed that can be developed, and the speed of the car is not very high. torque It is responsible for the intensity of this speed.
The higher the torque on the driving wheels, the faster the car gains momentum. This is especially noticeable when overtaking on country roads. If the engine has a “failure” in thrust at medium speeds, the driver will have to switch to a reduced gear to spin the engine to the maximum recoil zone, which takes precious time and creates an emergency situation.
Engine elasticity is the ability of a car to accelerate without changing gears. A good reserve of torque allows you to feel confident in the flow, starting from 60 km / h in high gear. This is not only more comfortable for the driver, but also reduces the wear of the clutch and synchronizers of the gearbox.
It is also worth considering the gear ratio of the main pair and gearbox. Engineers can pull out a weak motor through short gears, but then the car will require frequent switching. A powerful high-torque motor allows longer gears, ensuring smooth and confident acceleration without having to keep your hand on the gearbox lever all the time.
Comparison of diesel and gasoline engines
The eternal confrontation between diesel and gasoline is based precisely on differences in torque curves. Gasoline enginesThey are usually highly rated. They give their maximum torque closer to the upper limits of the rev range (4000-6000 rpm), which requires active operation of the gearbox to maintain tone.
Unlike them, diesel-powered Due to the high degree of compression and ignition from compression, the peak of thrust is issued very early, often already by 1500-2000 rpm. This creates a feeling of “plug” traction, when the car is torn from the spot with almost no delay, even without deep pressing on the gas pedal.
Modern technologies such as turbocharging and direct injection blur the boundaries between these types of motors. Small gasoline turbo engines (ecobusts) can now produce a momentary shelf, comparable to a diesel, starting from 1700 rpm. However, diesel is still the king of traction in the segment of heavy SUVs and commercial vehicles.
| Comparison parameter | Gasoline atmospheric | Diesel turbo | Gasoline turbo |
|---|---|---|---|
| Peak torque | 3,500 rpm-5000 | 1500–3,000 rpm | 1500–4500 rpm |
| Elasticity | Medium | Tall. | Tall. |
| Fuel consumption | High-pitched | Low. | Medium. |
| Engine resource | High-pitched | Very tall. | Medium/High |
The choice between these types of engines should be based on driving style. For urban driving with frequent stops and starts, diesel or turbo petrol with an early moment will be ideal. For track races, where high speeds and power are important, classical high-speed gasoline is preferable.
Why does the diesel go down at high speeds?
A diesel engine is limited by the speed of propagation of the flame front in the cylinder. At too high revs, the fuel simply does not have time to burn completely, so diesel engines rarely twist above 4500-5000 rpm, unlike gasoline, which easily reach 7000+.
Role of transmission in force transfer
The transmission of the car performs the function of a torque converter. The engine can produce only 150 Nm, but thanks to the transmission and main gear, the force can be transmitted to the wheels several times more. This is achieved by reducing the speed of rotation: the lower the transmission, the greater the torque gain.
In the first transfer, the gain is maximum, which allows you to move a multi-ton car from place. In higher gears, the moment decreases, but the speed of rotation of the wheels increases. That is why when trying to move in the fifth gear, the engine stalls - it banally lacks the strength (moment) to overcome inertia without additional reinforcement by the transmission.
Automatic transmissions and CVTs play an important role in keeping the engine in the optimum torque zone. The machine itself will switch to the gear below if you sharply press the gas, providing maximum acceleration. The variator can keep the momentum at the peak of the moment, while the car accelerates, creating a specific sound background.
⚠️ Warning: Prolonged towing of the trailer or driving in deep snow in high gear can lead to overheating of the transmission and destruction of the clutch, as the engine will operate in the zone of insufficient torque, requiring constant slipping of the discs.
All-wheel drive also affects the realization of the moment. The all-wheel drive system distributes traction between the axles, which allows for more efficient use of available torque, especially on slippery surfaces. If one axle starts to slip, the moment is redistributed to the one where there is a grip on the road.
Torque and cross-country vehicle
For SUVs, torque is perhaps the most critical parameter. When driving on dirt, sand or steep ascents, the car needs to overcome the huge resistance of the ground. High speeds are often useless and even harmful, as they can lead to the burying of wheels.
An ideal off-road engine should have high thrust at the lowest rpm (less than 2000 rpm). This allows you to crawl up the slope or through the ford without the risk of stalling and without the need to feverishly work with the clutch. That is why off-road is so appreciated diesel engines and gasoline V8 large volume.
An additional tool to increase the passability is a lowering row in the transfer case (demultiplicator). Including the “downsizing”, the driver increases the torque on the wheels by 2.5-3 times, sacrificing speed. This turns a regular SUV into a traction winch capable of pulling itself out of any quagmire.
☑️ Pre-trip traction check
It is also important to consider that off-road is important not only strength, but also the ability to dose this strength. A sharp jump in the moment can lead to the failure of the wheel into a slip and loss of control. Modern electronic systems help smooth these peaks by simulating the work of an experienced driver.
Engine economy and resource
There is a direct relationship between torque and fuel consumption. An engine that has to run at high speeds to maintain speed (due to lack of torque at the bottom) consumes significantly more fuel. The earlier the traction is available, the higher the gear and lower the speed can be moved, saving resources.
However, constant driving at the lowest speeds, when the moment is not yet great, is also harmful. In this mode, the engine experiences high loads, detonation and incomplete combustion of fuel, which leads to the formation of soot and accelerated wear of the liners. It is necessary to find a balance and keep the momentum in the zone of confident traction.
The engine life also depends on the mode of operation. High torque motors at low revs usually experience less thermal and mechanical loads than high-speed units, forced to constantly operate in the red zone of the tachometer. This prolongs the life of the piston group and lubrication system.
The optimal engine mode for longevity is rev movement, where 70-80% of maximum torque is available.
It is worth remembering that chip tuning, aimed at increasing power, often goes against the resource. Software-based boost pressure increases torque, but the piston group may not be designed for increased loads, which will lead to major repairs ahead of schedule.
How to Read Characteristics Graphs
When studying the technical characteristics of the car on the Internet or booklets, it is important to be able to read the graphs of the dependence of power and moment on the speed. Usually the moment is depicted with a blue or green line, and the power is red. We are interested not only in the peak of the chart, but also in its form.
The ideal torque schedule looks like a gentle hill with a wide top. This means that over a wide range of revs, the car will behave predictably and dynamically. If the graph has the appearance of a narrow peak (needle), this indicates that the engine is “live” only in a narrow corridor of revolutions.
Pay attention to the intersection of the power and moment curves. In internal combustion engines, they always intersect at around 5252 rpm (in pound-foot) or have a certain mathematical relationship in Nm. But what matters is how quickly the moment drops after it reaches the peak. A gentle descent is better than a sharp cliff.
What is a torque shelf?
A torque shelf is a rev range in which the engine produces at least 80-90% of its maximum value. The wider this shelf, the more comfortable and dynamic the car in everyday operation, as less gear shifts are required.
Can we increase the torque?
Yes, this can be done by installing a turbocharger, replacing camshafts with more productive ones, improving intake and output, as well as flashing the ECU. However, any intervention must be consistent with the strength of the engine parts.
Why are electric cars so fast?
Electric motors give the maximum torque instantly, with 0 rpm. They don’t have to wait for pressure buildup or flywheel spin, which provides phenomenal acceleration from a standstill that most ICEs can’t.
Does the fuel quality affect the moment?
Yes, using fuels with a low octane number (for gasoline) or cetane (for diesel) can lead to detonation or improper combustion. The ECU of the engine in this case adjusts the angle of ignition advance, artificially lowering the torque to protect the engine.
What's the best moment for the city?
For the city, a low and medium range of revolutions (1500-3500 rpm) is critically important. High revs in urban traffic are rarely used, so the engine with an early moment will be much more economical and pleasant to manage.