In the age of 10-speed gearboxes, it can be a little hard to imagine a car with only one gear. As electric cars continue to grow in market share, the age of 1-speed gearboxes may just be getting started.
Internal combustion engines have always had gearboxes with some number of gears to allow for better gearing at different speeds. This is all pretty standard when it comes to car ownership. However, whether you realize it or not, electric cars don’t typically have gearboxes with more than one gear. So, how can an electric car function without a multi-speed gearbox when internal combustion engines need gearboxes? It all has to do with RPM and power.
Internal combustion engines only generate useable torque and power output in a small range of engine speeds. This is why if you leave a manual car in gear while going a slow speed, it stalls out. Most ICEs can’t operate below about 750 RPM. To accelerate an ICE, multi-speed transmissions are necessary to translate the engine’s narrow power range into a wide range of speeds. When your car is in first gear, you can easily hit speeds of up to 30 miles per hour, but no way could a car go highway speeds with this low gearing.
Internal combustion engines need gearboxes because their usable torque and power output RPM range is fairly slim. For electric engines, this isn’t the case.
Electric motors generate 100% of their torque as soon as they are triggered. This principle is why you can do things like this in a Tesla.
With this instant supply of torque to the wheels, electric cars are extremely powerful off the line. However, most electric motors’ torque trails off at higher RPMs, meaning that gas powered cars can win out in higher rev ranges.
The simple fact of the matter is, however, that since torque is applied from the bottom all the way up to the top of an electric motor’s rev range, there’s no need for a gearbox. The operation RPM range for electric motors extends into every possible speed the car would need.
Electric cars can have multi-speed gearing, it’s completely feasible, but it is completely unnecessary given what is being demanded from the motor output. If you design a multi-speed transmission into an electric car, all it would do is add complexity, weight, and inefficiency into the design. The Tesla Model S has a single speed gearbox with a ratio of 9.73:1. This step-down transmission allows the car to handle the higher rev output of the electrical motor without excess wear. If the gear ratio was 1:1, it would be theoretically possible to spin the wheels of the car at 10,000 RPM, which isn’t exactly safe or necessary. Most electric motors in modern EVs are capable of up to 20,000 RPM, so some form of singular step down gearing is necessary.
The short video from Engineering Explained below will take you into a little more of the mathematics behind gearboxes in cars as well as one area where EVs are fitted with multi-speed gearboxes for performance.