EV Chassis and Motion Systems

Finding

Braking, steering and suspension are converging into one software-controlled motion domain, and Chinese automakers and suppliers are shipping each by-wire step first

Most EVs now use decoupled one-box brakes that blend motor regeneration with friction braking. Tesla's Cybertruck (2023) and NIO's ET9 (2025) ship with steer-by-wire and no mechanical column link; BYD's DiSus and NIO's SkyRide put active suspension into volume Chinese models. The next step, dry electromechanical brakes (EMB) with no brake fluid, is being readied by Brembo, ZF, Bosch and Chinese suppliers including Bethel.

The motion stack has four layers: a vehicle dynamics controller that supervises the whole vehicle, brake controllers and actuators, steering controllers and actuators, and suspension actuators and dampers. The controller fuses wheel-speed sensors, the inertial measurement unit, steering angle, ride height, brake pressure and motor torque estimates, then commands the actuators within milliseconds. EVs make that coordination harder and more valuable: instant motor torque, regenerative braking, a low center of gravity and 20-30% more mass than a comparable combustion car all change how the vehicle pitches, rolls and loses grip.

Braking changed first because it sets range. The traction motors handle most deceleration through regeneration, so the friction brake must blend seamlessly with the motor and stay available for emergencies. That pushed automakers from vacuum boosters to decoupled electro-hydraulic one-box units - Bosch's IPB, ZF's IBC, HL Mando's IDB, Aumovio's MK C2 and, in China, Bethel's WCBS - which also give automated driving systems direct brake authority. Steer-by-wire removes the column: a road-wheel actuator steers and a separate feedback motor gives the driver feel, both on redundant electronics at ASIL D. Tesla's Cybertruck, NIO's ET9 and the Lexus RZ (built by JTEKT) are in production.

Value is moving from castings and hydraulics into controllers, sensors, motors and software, so suppliers now have to deliver diagnostics, software interfaces and safety cases with the hardware. Automakers choose between buying best-of-breed brake, steering and damper systems separately or handing the integrated motion stack to fewer suppliers; Tesla, BYD and NIO keep the coordinating software in-house. Nexteer, a top steering supplier, is owned by China's AVIC; Bethel and Tongyu have taken one-box brake share in Chinese EVs; and Tuopu and Baolong build air suspension that was once imported. Zonal electrical architecture and 48 V low-voltage systems, as in the Cybertruck, make the actuators easier to power and network; see Zonal Architecture.

Motion layers

The Four Layers of the Motion Stack

Each layer with its elements, the engineering challenge and who supplies it; Chinese suppliers follow the semicolon.

By-wire steps

Each Function's By-Wire Step and How the Layers Interact

What changes as each function goes by-wire, the first production vehicles, and why the layers cannot be tuned separately.

Suppliers

Chassis and Motion Suppliers

Brake, steering and suspension suppliers with by-wire products, Chinese suppliers included.

Standards

Rules That Govern By-Wire Chassis

By-wire actuators must fail operational, not just fail safe: a single fault cannot remove steering or braking.

Related

Related coverage

• EV Networking and Communications
• EV Safety and Redundancy Hardware
• Zonal Architecture
• EV Platforms
• E-Axle
• Smart Cabin Systems
• SDV Systems Supply Chain
• Domain Control Units