Umair Gaines
Electric supercars, like most electric vehicles, do not require multiple gears because they have an electric motor instead of an internal combustion engine. Electric motors deliver their maximum torque at zero RPM, meaning they do not need a system to disconnect them from the drivetrain to allow them to idle while the vehicle is stopped. Electric motors also have a much larger RPM range than internal combustion engines, and they make their best power output over a broad RPM range. This means that electric supercars can reach top speed in a single gear, without the need for a multi-speed transmission.
| Characteristics | Values |
|---|---|
| Electric motors deliver maximum torque at zero RPM | Unlike internal combustion engines, electric motors do not need a system to disconnect them from the drivetrain to allow them to idle while the vehicle is stopped. |
| Electric motors have a much larger RPM range | Electric motors can rotate up to 20,000 RPM, while internal combustion engines typically reach 4,000-6,000 RPM. |
| Electric motors have high torque from zero RPM | Gearboxes are torque-multiplying devices, but with high initial torque, there is no need to multiply it using multiple gear ratios. |
| Electric motors have high RPM capability | The high RPM capability of electric motors means that top speed can be achieved with just one ratio. |
| Electric motors have electronically limited top speeds | The electronically limited top speed of an electric car means that a single gear is sufficient. |
| Electric motors deliver power instantly | Electric motors do not need to gain torque through revving, unlike conventional vehicles. |
| Electric motors are power-efficient throughout their rev range | Electric motors deliver optimum performance across a wide range of revs, while internal combustion engines only perform optimally within a narrow band. |
| Electric motors do not have a clutch | Electric vehicles do not have a clutch, only a brake and an accelerator. |
| Electric motors are ~95% efficient across their entire rev range | Electric motors are highly efficient, while internal combustion engines are less efficient due to friction and heat loss. |
| Electric motors do not require engine oil | Electric vehicles do not have internal combustion engines, so they do not need engine oil to reduce friction and control temperature. |
| Single-gear electric vehicles are cheaper and less complicated to manufacture | Installing a driveline system with multiple gears adds cost and complexity to the manufacturing process. |
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What You'll Learn
Electric motors have a much larger RPM range than combustion engines
The high torque produced by electric motors at low RPMs, or even from zero RPM, is another critical factor. Torque is the twisting force that drives a vehicle forward. In combustion engines, gearboxes are necessary to multiply torque at low speeds. However, electric motors inherently produce high torque without the need for gearboxes, as they can deliver maximum torque at stall. This high torque at low RPMs allows electric cars to achieve excellent acceleration without the need for multiple gears.
The broad RPM range of electric motors also contributes to their efficiency. Unlike combustion engines, which are efficient only within a narrow band of RPMs, electric motors maintain power efficiency across their entire rev range. This efficiency means that electric motors deliver optimum performance at various speeds without requiring a specific rev range suited to low-speed driving or acceleration.
While most electric cars have a single-speed transmission, some manufacturers are developing two-speed gearboxes. The Porsche Taycan and Audi e-Tron GT are notable examples of electric vehicles that utilise a two-speed gearbox for improved performance and range. However, the extra complexity and cost associated with multiple gears have typically outweighed the potential benefits for mainstream cars.
In summary, electric motors' large RPM range, high torque at low RPMs, and power efficiency across their rev range contribute to their ability to deliver outstanding performance without relying on multiple gears. The inherent characteristics of electric motors have revolutionised automotive engineering, challenging the traditional reliance on gearboxes in combustion engines.
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Electric cars don't need gears to multiply torque
Gears change the amount of torque that reaches the wheels from the engine. In a typical internal combustion engine, gears are necessary to amplify the force of the engine so that more torque makes it to the wheels. This is because combustion engines do not generate enough torque to move the car smoothly or efficiently.
However, electric motors have a much larger RPM range than internal combustion engines and can produce high torque from zero RPM. This means that even at low RPM, there is enough torque to move the car. Therefore, electric cars don't need gears to amplify the power to the wheels and can be listed as "direct drive".
The high torque produced by electric motors can cause significant durability concerns for multi-gear transmissions. The torque produces very high internal loading on the teeth of the reduction box and the sideway loading on the internal shafts, as well as the motor shaft and couplings. This is believed to be the issue with some Tesla models, where users have experienced problems with their drive trains.
While most electric cars have a single-speed transmission, some supercars like the Porsche Taycan and Audi e-Tron GT employ two-speed gearboxes. Manufacturers are currently developing two-speed gearboxes for electric cars, but the extra complexity and high price currently outweigh the potential benefits.
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Electric motors deliver power instantly
This instant torque is a unique feature of electric motors, and it is this property that allows them to deliver their maximum torque at zero RPM. In contrast, internal combustion engines require a system to disconnect them from the drivetrain when idling, and they also have a more limited RPM range. Electric motors, however, have a much broader RPM range, and they make their best power output across this entire range.
The high torque at zero rpm means that electric motors do not need a gearbox to multiply torque as IC engines do. Gearboxes are used to stay within the optimal RPM range, but electric motors have a much larger RPM band and do not need to be geared down to get a vehicle moving. This means that a single gear ratio can be chosen to provide a good compromise between acceleration and top speed.
While some electric cars, like the Porsche Taycan and Audi e-Tron GT, do use a two-speed gearbox, the majority use a single-speed transmission. This is because the high torque output of electric motors can cause significant durability concerns for multi-gear transmissions. The instant torque of electric motors can also be utilised in other applications, such as torque motors in force feedback steering wheels for computer gaming.
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Multi-gear transmissions are complex and expensive to manufacture
Electric supercars do not require multi-gear transmissions because electric motors produce a consistent amount of torque and deliver power instantly. This means that the process of gaining torque by revving, which occurs in conventional vehicles, is not required in electric supercars.
The high torque produced by electric motors also results in very high internal loading on the teeth of the reduction box, the sideway loading on the internal shafts, and the motor shaft and couplings. This causes significant durability concerns for multi-gear transmissions. The immense torque that electric motors produce at zero RPMs can cause issues for multi-gear transmissions, as seen in the first-generation Tesla Roadster prototypes, which had two-speed transmissions that were replaced with single-speed transmissions after the two-speed transmissions failed due to the torque.
Additionally, multi-gear transmissions are complex and expensive to manufacture. From a manufacturing standpoint, the biggest advantages of having a single gear for an electric motor are cost and simplicity. Installing a driveline system with multiple gears adds cost and complexity, increasing the car's price.
While some electric cars do use multi-gear transmissions, such as the Porsche Taycan and Audi e-Tron GT, which use a two-speed transmission for the rear motor, these transmissions are technically difficult to handle the immense and instant torque of electric motors. Therefore, the extra complexity and high price of multi-gear transmissions currently outweigh the potential benefits for most electric car manufacturers.
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Electric motors deliver maximum torque at zero RPM
The high torque of electric motors at zero RPM is due to the fact that torque is determined by the strength of the magnetic field, which is determined by the current through the motor. With a high enough voltage, a high current can be produced, resulting in maximum torque at any RPM. Additionally, electric motors have a much larger RPM range than internal combustion engines, allowing them to maintain high torque over a broad RPM range.
The instant torque produced by electric motors at zero RPM gives electric cars their characteristic quick acceleration from a stop. This is achieved without the need for a system to disconnect the motor from the drivetrain when the vehicle is stopped, as is required in internal combustion engines.
While most electric cars have a single-gear design, some manufacturers are developing two-speed gearboxes for electric vehicles. However, the extra complexity and high price of these gearboxes currently outweigh the potential benefits.
In summary, electric motors' ability to deliver maximum torque at zero RPM eliminates the need for multiple gears in electric supercars, resulting in efficient and quick acceleration.
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Frequently asked questions
Electric supercars don't require gears because electric motors produce a consistent amount of torque and deliver power instantly. Electric motors also have a much larger RPM range than internal combustion engines, so they can achieve high speeds without the need for multiple gears.
The main benefit of electric supercars not having gears is simplicity and cost. Installing a driveline system with multiple gears adds complexity and cost to the vehicle. Electric supercars also benefit from not having a traditional transmission system, which reduces friction and improves energy efficiency.
While most electric supercars do not have gears, there are some exceptions. For example, the Porsche Taycan and Audi e-Tron GT use a two-speed gearbox in the rear motor. The BMW i8 also has a two-speed transmission, but it is only used in pure EV mode. Some manufacturers are currently working on developing two-speed gearboxes for electric vehicles, but they are not yet widely available.
