Performance

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When buying a car one usually asks for the horsepower, maximum torque or other metric explaining the capability of the motor. With electric cars you can also measure power and torque but comparison with petrol cars is not straight forward.

Watch this video to learn about torque:

Petrol cars need to build up engine speed before any torque can be produced. Maximum power only occurs as a short burst near the engine speed limit. The full power is therefore inaccessible to most drivers except for trained racing drivers. Full power also puts high strain on the engine and will make lots of noise.

Electric cars on the contrary have full torque from standstill, and full power as soon as the speed reaches approx. 40 km/h. The power stays on full all the way to top speed, which is typically limited by electronics.

This means that the full power and torque of an electric car is accessible for any driver in almost any situation. Using the full power will not strain the engine nor produce noise.

As a rule of thumb one electric kW equals 1½ traditional engine kW. This is not a scientific rule but is based on the typical acceleration feeling of cars in real life.

If you are currently driving a 100 kW petrol car you should be satisfied with an around 67 kW electric car.

Electric cars generally have lower top speed (typically 130 - 160 km/h) compared to petrol and diesel cars (typically 180 - 250 km/h). This is down to two reasons mainly. Exceptionally high speed requires exceptionally high power and will therefore drain the battery very quickly. Driving at 200 km/h would drain the battery 8 times as fast as driving at 100 km/h. Secondly electric cars are typically equipped with only 1-speed transmissions where conventional cars have 5-8 speeds. This means that top speed has to be limited in order not to over speed the electric motor.

Figure 6: The propulsion of a 70 kW electric car

Figure 7: The propulsion of a 110 kW petrol car with 6-speed transmission

Electric motors have high torque normally expressed in Nm. This property is often associated with heavy towing capability. However electric cars are rarely fitted with tow bars and are not particularly suitable for towing.