![[For beginners] What is the difference between maximum power and maximum torque in a motorcycle’s specifications?](https://motopeek.com/wp-content/uploads/2024/10/4272-1760972833750.jpg)
What are maximum power and maximum torque?
In recent years, spec sheets have come to express maximum power output in units such as “kw [PS]/rpm” and maximum torque in units such as “N・m [kgf・m]/rpm.”
For example, on the Honda Rebel 250 ,
Maximum output 19kW [26PS] / 9,500rpm
Maximum torque 22N・m [2.2kgf-m] / 6,500rpm
This is how it is written.
Honda Rebel 250
In recent years, maximum power output has come to be expressed in kW and maximum torque in N-m, both of which are international standards. However, until recently, in Japan, maximum power output was expressed in PS and maximum torque in kgf-m. For long-time motorcycle riders like me, these are more familiar and easier to visualize. For this reason, it is now common for Japanese manufacturers to list both figures on their spec sheets.
Just to be safe, these can be converted as follows:
Output: 1PS = 0.7355kW
Torque: 1kgf・m = 9.80665N・m
Also, the rpm at the end of each number refers to the engine speed, and indicates at what revolutions each number occurs.
Why write two?
Of these, maximum output roughly indicates “how much power the engine can produce at its maximum.” It is the equivalent of “horsepower.” Maximum torque also refers to the maximum value of the “rotating force = torque” generated by the engine’s crankshaft.
So why are these two figures displayed on the spec sheet? The answer is that power output and torque are closely related.
The relationship between power output and torque is often compared to a bicycle. In the case of a bicycle, torque is the force applied when you push down on the pedals. The greater the force applied, or torque, the faster the bicycle will accelerate. In the same way, in the case of a motorcycle, torque has a significant relationship with acceleration performance.
In the case of a bicycle, the force exerted on the pedals is torque.
On the other hand, power output is torque multiplied by the number of revolutions of the pedals. It can be expressed by the formula “power output = torque x number of revolutions.” And since the greater the power output, the easier it is to increase speed, power output is an indicator that has a strong relationship with speed.
The greater the power output, the easier it is to achieve speed.
Maximum power and torque are not always available.
Given this relationship, we can roughly say that maximum output is the maximum amount of power (horsepower) required for a motorcycle to gain speed, and maximum torque is the maximum amount of power required to accelerate the vehicle.
However, in both cases, this force is not always present, and the largest value is reached at the rpm (rotational speed) mentioned above. Furthermore, even if the same engine with the same displacement is installed, the value may be changed depending on the characteristics of the bike.
For example, take Honda’s Africa Twin series 1082cc water-cooled 4-stroke inline 2-cylinder engine. Although they are equipped with the same engine, the adventure model CRF1100L Africa Twin and the cruiser model Rebel 1100/T have different power and torque outputs as shown below.
[ CRF1100L Africa Twin]
Maximum power output 75kW [102PS] / 7,500rpm
Maximum torque 112N・m [11.4kgf-m] / 5,500rpm
CRF1100L Africa Twin
[Rebel 1100/T]
Maximum power output 64kW [87PS] / 7,000rpm
Maximum torque 98N・m [10.0kgf-m] / 4,750rpm
Rebel 1100
The CRF1100L Africa Twin has higher maximum power and torque figures. However, the Rebel 1100/T generates both at lower RPMs. This means that power and torque are generated at lower speeds, which can be expected to result in smoother acceleration when starting off. In contrast, the CRF1100L Africa Twin seems to be set up to deliver more power at higher RPMs.
Looking at these figures, we can see that even with the same engine, the settings are changed to suit the type and characteristics of the bike, which allows each model to have a more individual riding feel.
In any case, the maximum power and torque figures are indicators of what kind of riding experience and engine feel a particular bike will have. For example, they are one of the specs you should take into consideration when purchasing a new bike.
