Torque vs Horsepower : What’s the difference? In this article I explain torque in detail, providing plenty of examples so that it will make sense to you. Many people like to throw around the word “torque” when it comes to cars, but in truth, I don’t think most people understand what they’re talking about.
Car manufacturers are always boasting about horsepower (HP). We automatically assume that the car with most horsepower or kilowatts will be the fastest. There’s another specification that people don’t always understand as easily. Torque is an equally important specifications and does not only apply to car engines. In fact, the engine is only one aspect of how torque works in a car. This article is going to explain how torque works and the relationship between horsepower and torque.
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Torque vs Horsepower
What is torque?
Torque is force multiplied by distance. In other words, one foot-pound (FT LBS) of torque is the equivalent of applying one pound of force over a distance of one foot. We can simplify this example even further by imagining a lever, like bicycle pedal or wrench. Both a wrench and bicycle pedal utilize torque to perform a task. Pressure, or force is applied to create a circular, twisting motion.
VIDEO \ What is Torque — Explained
If we place a 1-pound bag of sugar onto a bicycle pedal with a 1-foot crank, we are generating 1 Ft LBS torque. If we place another 1-pound bag of sugar onto the pedal, we will double the force, creating 2 Ft LBS torque. Similarly, we can increase the length of crank connected to the pedal to 2-feet. This will have the same effect, doubling the torque to 2 Ft LBS.
Mechanics know this principle all too well. If you try loosen a bolt using a regular socket wrench, with a handle that’s a about 1-foot in length, it will takes quite a lot of strength to push down on the handle in order to twist the bolt. When the bolt is really tight, like a large wheel lug, you probably won’t have any success using a short wrench. If you use a longer wrench, to increase the distance, you will be able loosen that bolt without requiring more strength. This is because the torque created as you push is increased by the additional length of the wrench.
Torque Line of Action / Diagram
Torque is : “…the line through the point at which the force is applied in the same direction as the vector…”
Wikipedia / Line of Action
What is Horsepower?
Horsepower is the rate at which work is accomplished. Essentially, this is speed multiplied by distance. If two identical cars are fitted with different engines, they will have a difference in power. It seems only logical that the car with the most powerful engine will in a race. Right? It’s not actually that simple. A car is more than just an engine, there’s a transmission that can change the entire dynamics of torque vs horsepower.
This means that one car may be faster over a shorter distance, regardless of the horsepower provided by the engine. It will depend on the gear ratio which determines how much torque is transferred to the wheels.
While this may seem a little complicated right now, it will become easier to understand as we take a deeper look into what torque does in a car. Torque in the engine will not always be the same as torque at the wheels.
There is a relationship between torque and horsepower: HP = Torque X RPM. If you make a more analytical observation of car torque vs HP specs, you will see that an engine has a maximum torque spec and a maximum HP spec. Both these specifications are relative to engine speed or RPM. An engine will reach its maximum horsepower at a certain RPM and maximum torque at a different RPM.
To get the best performance from an engine, the relationship between torque and horsepower needs to be optimized. However, best performance is not the same thing for all situations or vehicles.
If you want to get somewhere in the shortest time, you want to drive as fast as possible. You want to do the most work in the shortest time. When speed is the objective, horsepower is important, as this is the rate (or speed) at which the work is done.
If you want to move more weight and are not too concerned how fast this is achieved, higher torque is advantageous.
There’s another factor that influences how we interpret the importance of torque vs horsepower. Inertia is the physical property that causes an object to remain in its present state of motion unless an external force is exerted. This means that if a car is stationary, an external force has to be applied to cause it to move. It requires more torque from the engine to overcome inertia when a car starts from a stationary position. Once the car is moving, less energy is required to keep it moving in that direction. Alternatively, a moving car will continue to move in the same direction unless a force is exerted in the opposite direction.
When you move away from a traffic light, your car needs more force to accelerate from 0 MPH to your desired speed. That force is provided by the engine in the form of torque. When you reach the next traffic light, and need to stop, force is applied to the brakes, creating friction which stops the car. If you select a lower gear, this can also slow the car.
Now we’re beginning to understand the real relationship between horsepower and torque. Gear ratios, whether in a car, lawnmower, or power tool, forms the essence of how horsepower and torque combine to exert the necessary force to meet varying requirements.
In a car, toque starts at the engine and ends up at the wheels. The wheels will not generally move at the same speed as the engine. Gears can increase speed and decrease torque, or do the opposite, decrease speed, and increase torque. A power saw, uses the same principle, with power being created by an electric motor, which is then transferred to the blade. The blade will not move at the same speed as the motor. The speed will be relative to the gear ratio. In both cases the HP will be transferred by means of gears to provide the requisite torque.
To get the full picture, we need take a step-by-step look at how torque works in the engine and then how this is transferred to the wheels of a car.
VIDEO | Horsepower vs Torque
What is Engine Torque?
A car engine works by creating a force that acts upon the piston. Fuel and air are ignited in an enclosed space, or vacuum. The hot air expands which forces the piston to move. As the piston moves downwards, it pushes a connecting rod which rotates the crank shaft.
This means that engine torque is the force caused by energy from burning fuel. Since torque is force multiplied by distance, the length of the piston connecting rod will affect how much torque an engine produces. The distance that a piston is able to travel is known as the stroke.
This means that an engine with a longer stroke will develop more torque. However, there are limitations as to how long a piston stroke can be. This will be determined by the size of the engine and the strength of the materials used. A longer connecting rod is not as strong as a shorter one. Therefore, as we increase the torque, by increasing stroke, we increase the risk of breaking the connecting rod.
Creating additional torque, using a longer stroke, will restrict engine RPM. The piston moves in a linear motion, turning the crank shaft in a circular motion. This means that as the piston moves past 50% of the stroke, the angle of the connecting rod becomes offset. The piston is moving in a straight downward motion, but the connecting rod will follow the rotation of the crankshaft, causing it to tilt to one side. This disturbs the balance of the engine, causing increased vibration at high RPM. Engineers perform detailed calculations to maximize all these physical properties.
Since horsepower is equivalent to torque multiplied by RPM, engineers need to find the perfect balance between optimizing both torque and horsepower. Not all engines are used for the same purpose.
A performance car, designed for high-speed driving, will developed to produce maximum horsepower, whilst compromising on torque. A high performance racing engine achieve high RPM without damaging the engine. An engine used for a truck, will favor torque over horsepower. A diesel engine with a longer stroke, moving relatively slowly, will provide high torque at low RPM. This increases the torque produced by the engine but reduces the speed. Additional torque allows a heavy vehicle to overcome inertia more easily. Inertia is relative to weight. A heavy vehicle will require more torque to apply the force needed to counteract this.
Transmission Torque
We will never fully understand what torque does in a car, without understanding gears. In the first example of torque being force X distance, I used an easy example, the length of a wrench handle or bicycle pedal. A gear uses the same principle of distance, but in a circular form not linear, like the previous examples.
When a small gear is used to drive a larger gear, the small gear will rotate more times than the larger gear. Basically, the larger gear is increasing the distance in the same way as a longer wrench handle does when loosening a bolt. By increasing the distance, torque is increased proportionally.
If a larger gear is used to drive a smaller gear, the opposite effect is achieved. The smaller gear will rotate more times than the larger gear, increasing speed and reducing torque.
A car transmission uses a large gear propelled by the engine to drive smaller gears that finally drive the wheels. The gear ratio is the difference in size between the large drive gear and the smaller driven gear. If the gear ratio is 1:3, it means that the driven gear is three times smaller than the driving gear.
A vehicle transmission system uses different gear ratios to control torque and speed. A low ratio gear is used to provide maximum torque when the car needs to start moving. The highest gear ratio is used to achieve maximum speed.
This means that a high torque engine can achieve greater speeds with a high ratio gear. Conversely, a low torque engine can produce more force using a low ratio gear. Since gearing allows us to alter the amount of torque or speed that we require, why is engine HP or torque that important?
To answer the question of engine torque vs transmission torque, we need to take a look at the evolution of the automobile. Over the last century, engineers have experimented with every concept of automotive design and propulsion.
The greatest changes in auto engineering happened after WWII. The 1950s defined the future of the cars that we now drive today. During this era there was a great difference in the approach that engineers took when developing engines and transmission systems. In those early years, American and European auto manufacturers decided on two opposite ways of dealing with torque vs horsepower to maximize vehicle performance.
By looking at how the early American cars differed from their European counterparts, we can easily see how we can use different types of engines to provide the power we need, by using a transmission.
Evolution of the Automobile
In the heyday of the modern car, American manufacturers decided that automatic transmission was the future of the automobile industry. Today, it is clear that they were correct. However, back in the 1950s, automatic transmission systems were crude and not at all efficient. The first automatic cars had only two gears (high or Low) and had no torque converter to allow for a smooth transition between these two speeds.
As a result, the gear ratios were not that effective at providing the optimum amount of low-speed torque or highspeed horsepower. Since the transmission utilized only two gear ratios, the engine had to be able to provide a lot of torque and horsepower to compensate for the limited abilities of the transmission.
In order to accelerate and achieve a reasonable speed, American cars used really large engines, preferably in a V8 formation which can provide the most torque and horsepower at a lower RPM. This meant that the car would have enough power to pull away in low gear and still reach a reasonable speed as the RPM increased. High gear would only engage when the car was travelling relatively fast.
Considering the limitations of early automatic transmissions, European auto manufacturers decided that a manual transmission was the best option. This meant that these cars could be fitted with much smaller engines. Because the manual transmission of that time utilized four gears, they were much more efficient than the 2-speed automatic cars. By using 4 gears, it was possible to optimize torque for acceleration, with a very low ratio. The gear ratio could be gradually increased as you change the gears. Moving from one gear to the next increased the ratio, reducing torque and increasing speed.
In the end, a 4-speed manual transmission, using a small 4-cylinder engine, was much more efficient than the 2-speed automatic cars that required a larger engine. Though things did not remain this way.
American engineers, never gave up on the merits of an automatic transmission. After all, these cars are much easier to drive. In the end, a car that is easier to drive will be safer. A driver that is not concerned with the technicalities of a clutch and changing gears can focus their full attention on the business of driving the car.
By the 1960s, the planetary gear, which is essential for an automatic transmission, started to evolve into a more sophisticated form. The Chevrolet “Tri-Matic” was the first 3-speed semi-automatic transmission. While the driver was required to shift the gears, the car did not require a clutch. Soon after, the 3-speed automatic transmission became common throughout the world. By using a torque converter to control the transition between gears, automatic cars became smoother and more efficient.
While the 3-speed automatic transmission was not quite as efficient as the 4-speed manual, it was a great improvement. As manual transmission systems started to increase gear ratios, from four to five gears, the 3-speed automatic transmission was losing some ground in the race for efficiency. When oil prices started to increase during the 1970s, the need for more efficient cars became increasingly important.
A three-speed automatic transmission would still require more engine power to provide the same torque and speed, when compared to a 5-speed manual transmission. Fitting an overdrive to the automatic transmission helped by transferring the power directly from the engine to the wheels. This meant that it used a 1:1 gear ratio. However, using an overdrive greatly reduced the torque at the wheels. It could only be engaged once the car was traveling fast enough. As the car approached an incline, which requires more torque to maintain motion, overdrive is ineffective. The car will decelerate rapidly, unless overdrive is disengaged before the extra torque is required. An automatic transmission will only react once the wheels begin to slow down. This meant that the driver would have to disengage the overdrive before approaching the incline if they wished to maintain a reasonable speed.
In the 1990s manual transmission systems continued to evolve by increasing the number of gears. The 6-speed transmission was even more efficient than the preceding 5-speed. In order for automatic transmissions to compete, the traditional planetary gear, used for the 3-speed transmission, had to be improved upon. By adding an additional planetary gear, using various combinations to provide increased gear ratios, automatic transmission systems moved from 3-speed to 4-speed. The gear ratios continued to increase, and the use of a transmission computer made the automatic transmission even more responsive and efficient.
Today, an automatic transmission will typically have up to eight gear ratios, some have even more. Improved clutches and torque converters have made gear transition almost seamless. Using a computer, the car is able optimize the transmission for economy or speed, depending on the driver’s choice. The modern automatic transmission is almost as efficient as the manual equivalent.
Engines have also evolved in many ways. By using variable valve timing (VVT), engines can now produce more torque when required, then speed up to produce more horsepower as the RPM increases. The combined effect of improved engine and transmission technology means that a modern car, using a small engine, will perform substantially better (using a lot less fuel) than the old gas guzzlers of before.
One may think that we’ve reached the pinnacle of automotive engineering. Cars are super-efficient, fast, and relatively safe. It is not human nature to stop innovating. Engineers are always going to try improve on what seems like the best technology possible. It’s what we do.
The future of the automobile is probably going to look very different than it does today. It has already begun to evolve, thanks to manufacturers like Tesla. The gas engine and traditional transmission will soon become redundant.
Torque and Electric Cars
By replacing an internal combustion engine with an AC induction electric motor, the car has been revolutionized in more ways than most are aware. The Zero emission electric motor has the caught the attention of people who want to reduce our impact on climate change. Though there are many more advantages to this technology. The efficiency, along with the ability to manage both torque and horsepower, makes this best method automotive transport.
The basic power supply for an electric car utilizes an inverter which converts the DC power from a battery into high-voltage AC power for the electric motor. The advantages of using an inverter with a computerized management system is what makes the electric car such an efficient machine. This is because engine torque and horsepower can be managed electronically by changing the voltage and frequency to exactly meet the demand.
An electric motor is not a complicated machine. Instead of the hundreds of mechanical components used for an internal combustion engine, the electric motor basically consists of a rotor and several stators. This improves the power to weight ratio, reduces maintenance, and increases durability. There is very little that can go wrong with an electric motor compared to a gas engine. The greatest advantage is much better energy efficiency and the ability to control how that energy is used.
The computer controlling the inverter requires only a small amount of data: throttle position, wheel speed, and motor speed. The primary input data is supplied by the throttle. This conveys the driver’s intention – accelerate, maintain speed, or decelerate. By monitoring wheel speed relative to motor speed, the computer will adjust the amount of torque or horsepower produced by the motor to meet the requirements of the driver.
The inverter will calculate the precise electric current required to produce optimum torque and horsepower for any driving situation. Unlike a gas engine, there is no compromise between torque and horsepower. There is also no need to achieve optimum RPM for the requisite torque or horsepower to be produced. Both torque and horsepower are delivered as required, without restrictions.
Because the electric motor produces exactly the right amount of horsepower and torque at all times, there is no need for a conventional transmission. This further reduces the need for complex mechanical components. An electric car only has two gears that remain permanently engaged. There are no gear changes like a conventional transmission. Power is transferred directly from the motor to the drive shaft via a drive gear, with a final gear reduction is at the differential. The purpose of these gears are simply to allow the electric motor to rotate more freely without laboring to provide extra torque to the wheels.
The electric motor can rotate at any RPM, depending on the current that is being supplied. To provide extra power at low RPM, when additional torque is required, the voltage and frequency are altered in accordance with the amount of friction at the wheels. If the wheels slow down, whilst the throttle position remains constant, the computer will instantly increase the torque to provide more direct power to wheels before the car begins to slow down.
By utilizing this power so efficiently the horsepower produced by an electric motor is far more than energy input that would be required for the same car using a gas engine. According to a Car and Driver article, the Tesla Model 3 has achieved 90% efficiency. By contrast, the average gas-powered passenger car is only 25% – 30% energy efficient.
