By Xu Shanshan, Edited by Li Motian
In November 2023, the long-awaited Cybertruck finally hit the market. During the launch event, which lasted less than 27 minutes and was watched by over a million people, Tesla unveiled a series of cutting-edge technologies, with steer-by-wire generating the most lasting impact.
Compared to traditional steering systems, steer-by-wire eliminates the steering column, completely replacing the mechanical connection between the steering wheel and the wheels with electrical signals.
As the world's first mass-produced vehicle to remove the steering column and feature steer-by-wire as standard across all trims, the 5.6-meter-long Cybertruck can easily achieve what Elon Musk calls "fighter jet mode": a slight turn of the steering wheel results in a sharp turn[1].
To integrate steer-by-wire into the vehicle, Tesla radically overhauled its architecture, abandoning the 12V low-voltage system in favor of a 48V platform, allowing power-hungry systems like steer-by-wire to operate at full capacity. Tesla even published this methodology and sent it to the headquarters of major automakers, with Ford publicly expressing its gratitude[2].
Regrettably, Tesla did not trigger a mass-production wave for steer-by-wire, nor did the Cybertruck shake the dominance of pickups in the US market.
It was not until 2024, when the NIO ET9 became the first mass-produced vehicle in China equipped with steer-by-wire and took the lead in participating in the formulation of new national standards, that this technology began to show signs of a boom.
Since the beginning of this year, multiple models such as the XPeng GX, IM LS8, and Li Auto L9 have explicitly featured steer-by-wire. Similarly, the new Lexus RZ and Mercedes-Benz EQS have also packaged steer-by-wire as a key selling point.
Compared to traditional steering systems, what exactly has steer-by-wire changed?
Turning the Steering Wheel into a Gamepad
The essence of steer-by-wire lies in the "by-wire" aspect.
In traditional steering systems, the steering wheel and the steering gear are connected via mechanical structures, commonly known as a "hard connection." Steer-by-wire, as the name suggests, removes the steering column and replaces it with wires, creating a "soft connection."
The operating modes also differ: one is equivalent to using a wrench to tighten a screw, where every movement is transmitted to the wheels with pinpoint accuracy; the other is like remotely controlling a robot to tighten a screw, where the steering wheel movement is translated into electrical signals by sensors, transmitted to the ECU (Electronic Control Unit), and the ECU issues commands based on actual conditions.
As a result, the force structure is vastly different.
For instance, when the automobile was first invented, it used a purely mechanical steering system without power steering, meaning the vehicle was pulled entirely by human power. Today, the mainstream EPS (Electronic Power Steering) system still relies on humans as the power source and commander, but the vast majority of the force is now provided by the electric motor.
In a steer-by-wire system, the force structure is straightforward, with the electric motor being the sole workhorse. Since the steering wheel and the wheels are completely decoupled, the force applied to the steering wheel is no longer transmitted to the wheels; instead, software and the electric motor are what truly make the wheels turn.
Based on steer-by-wire technology, the steering wheel is no different from a gamepad, but in real life, it is often necessary to create the illusion that the driver is exerting physical effort.
Since humans are the primary drivers of vehicles, simulating a realistic feel helps improve driving safety and control. The common practice is to integrate a road feel simulation motor into the steering wheel, using virtual resistance to replace road resistance and reduce the feeling of floatiness.
At this stage, the feel of steer-by-wire is relatively close to reality, but the actual experience far surpasses existing steering systems.
First, steering is more responsive. Based on steer-by-wire, the vehicle's steering ratio is dynamically adjustable.
The steering ratio, simply understood, is the ratio of the steering wheel's rotation amplitude to the wheels' rotation amplitude. The steering ratio for passenger cars is generally fixed at around 15:1, meaning that turning the steering wheel 15 degrees to one side results in a 1-degree deflection of the wheels.
The advantage of a large steering ratio is greater stability at high speeds, while the disadvantage is that it requires more effort to steer at low speeds during parking or U-turns.
Imagine a 5-meter-long mid-to-large SUV needing to make a U-turn in a narrow alley. The conventional approach is to turn the steering wheel all the way to the left by one and a half or even two full circles, reverse, and if one attempt fails, try again. The steering wheel would practically spark from friction, and passing the wheel from the left hand to the right hand leaves no room for elegance.
In contrast, the steering ratio of an F1 car is very small, set at around6:1 depending on track requirements, allowing the driver to easily navigate corners with only a slight turn of the steering wheel[2]. This is also why F1 steering wheels are becoming increasingly rectangular.
In comparison, because steer-by-wire lacks mechanical hardware connections, the steering ratio is not only unlocked but also naturally supports software definition.
Among domestic models equipped with steer-by-wire, the IM LS8 has a steering ratio as low as 4.5:1, requiring only half a turn to lock the steering wheel to one side, theoretically allowing for a half-yoke steering wheel.
Second, upgrading all four wheels to steer-by-wire allows for a smaller turning radius, making large vehicles more agile.
Taking the narrow-alley U-turn scenario as an example again, small cars are far more agile than large cars in alleys of the same width. The reason is that the rear wheels of traditional cars often cannot steer independently, especially at low speeds, where they basically remain stationary.
Therefore, for traditional cars with similar front-wheel steering angles, the longer the wheelbase, the larger the turning radius, and the more cumbersome the movement.
If the rear wheels are upgraded to steer-by-wire, they can steer in the opposite direction to the front wheels, shifting the center of rotation forward from the rear wheels and shortening the turning radius.
Currently, a transitional solution is "front-wheel steer-by-wire + rear-wheel active steering." The principle is similar, but the limitation is that the rear wheels are still connected via mechanical structures, making it difficult to unlock high-difficulty maneuvers.
In 2022, Mercedes-Benz offered owners of the entry-level EQS the option to pay for an upgrade of the rear-wheel active steering from 4.5° to 10°.
Steer-by-wire solves the practical challenges of driving large vehicles, but this technology was not originally designed with so many considerations in mind, and it had little to do with cars initially.
The Puzzle Piece of Chassis-by-Wire
The predecessor of steer-by-wire was not the automobile, but the fighter jet, a culmination of industrial technology.
In the aviation field, there is no so-called concept of steer-by-wire; instead, there is the Fly-by-Wire (FbW) flight control system, which encompasses all "by-wire" technologies.
The original intention of the earliest fly-by-wire flight control systems was simple: to simplify structures and reduce weight. In the 1930s, the Soviet ANT-20 (also known as Maxim Gorky), due to its massive size, took the lead in experimenting with fly-by-wire technology to reduce cable usage. However, this was still far from true "fly-by-wire flight control."
The first pure-blood fly-by-wire aircraft was the Canadian Avro CF-105 Arrow fighter jet. Despite a successful maiden flight, the government at the time canceled the development project, citing excessive cost burdens. The five prototypes were destroyed, and rumors say their remains were sunk into Lake Ontario[4][5].
It was not until the 1970s, in pursuit of ultimate maneuverability and comfort, that the F-16 fighter jet and the Airbus A320 eliminated mechanical connections and fully adopted fly-by-wire flight control systems, truly driving this technology to maturity.
This also provided an important reference for the automotive industry to learn from. It can be said that steer-by-wire is a flash of inspiration from fly-by-wire flight control applied to automobiles.
Early automotive companies attempted to remove the steering column in concept cars, primarily for two purposes: safety and leaving room for imagination in autonomous driving.
Removing the steering column between the steering wheel and the steering gear not only frees up more space in the front cabin but also prevents the steering column from striking the upper body and causing fractures in the event of a crash. For autonomous driving, steer-by-wire is also significantly safer.
Take response speed, for example. Traditional mechanical structures require layer-by-layer transmission, resulting in slow responses, while the average reaction time of human drivers is also relatively long, increasing risks.
An early study by MIT showed that it takes drivers approximately 390 to 600 milliseconds to detect a hazard and react[6]. Other studies suggest that 600 milliseconds is merely the median of human reaction times.
In contrast, steer-by-wire can break through the mechanical and physiological limits of humans, with response times as low as tens of milliseconds, curbing dangers at the source. This is also an indispensable capability for high-level autonomous driving.
A typical scenario is a high-speed tire blowout. In traditional cars, the steering wheel and wheels are connected via mechanical hardware, so the impact force naturally transmits to the steering wheel. Especially in the case of a front tire blowout, grip is instantly reduced, the car veers toward the blown tire, and the steering wheel spins rapidly in response.
If the traditional steering combined with human reaction time is slightly delayed, the vehicle is highly likely to lose control instantly, which in severe cases can be life-threatening.
Steer-by-wire, however, decouples the steering wheel from the wheels, allowing them to operate independently. The impact force generated by a blowout remains at the wheel end, and the system reacts much faster, significantly reducing potential dangers.
For example, during a high-speed tire blowout in the NIO ET9, the vehicle body can be controlled to experience only a slight yaw with almost no shaking. Within 300 milliseconds of the blowout, the vehicle can also quickly correct its trajectory[7].
In actual scenarios, because steer-by-wire is part of the chassis, it often needs to coordinate well with systems like the suspension when encountering extreme situations. In other words, the significance and value of steer-by-wire can only be maximized when placed within the context of the entire chassis.
For a long time in the past, due to slow progress, steer-by-wire was once considered the final puzzle piece of the chassis-by-wire.
Apart from technical difficulties and complex redundancy design, steer-by-wire has always been constrained by regulatory requirements. National standards explicitly stipulated that steering systems must retain mechanical connections. It was not until the new regulations coming into effect in July this year removed this mandatory requirement that the stumbling blocks for the implementation of steer-by-wire were completely cleared.
Behind the steering wheel, a revolution that has been dormant for many years has finally awaited the window for a boom.
References
[1] Cybertruck Unveiled: Bi-Directional Charging, Steer-by-Wire, Largest Battery in Any Tesla, Powered Frunk, 18.5-Inch Display, Not A Tesla App
[2] 'Great For The Industry': Ford, Others Get Tesla Cybertruck 48V System Specs, InsideEvs
[2] Why do car steering wheels need to be turned so many times to steer, and can it be done in one go like an F1 car?, Zhihu User
[3] This Time, Toyota Beats Tesla, autocarweekly
[4] MAGNIFICENT FAILURE, Vintage Wings of Canada
[5] From Lift Off to Legendary: The Lore Behind the Avro Arrow, The Royal Canadian Mint
[6] Study measures how fast humans react to road hazards, MIT News
[7] Tech Talk | High-Speed Tire Blowout: How to Handle It Safely and Calmly, NIO