“Brake”-Away EV Drive Tech Claims Net-Zero Unsprung Mass and 95% Efficiency

Wheely Nifty: The S‑Drive Concept

Simko’s S‑drive system rethinks electric propulsion from the wheel up. In a departure from conventional layouts, there’s no gearbox, differential, or half-shafts as with most in-wheel-motor solutions. Each 19‑in. wheel integrates an axial‑flux motor, brake system, suspension mount, and steering interface within a single modular assembly. The result is unsprung mass reduced to net zero with respect to conventional driven wheel hubs using half-shafts.

The S‑drive shown at CES 2026, captured in the accompanying video by Electronic Design's Bill Wong, targets sports‑car applications. Despite packaging the entire drive and brake functions inside the wheel envelope, Simko claims the system maintains comparable unsprung mass — around 60 kg per corner — to that of a standard hub, brake, and upright assembly.

Braking Conventional Thinking

Unlike traditional systems that chain multiple mechanical interfaces, S‑drive achieves over 95% peak efficiency by removing losses from gear reductions, extra bearings, and shafts. The 200-kW axial‑flux motor provides 600 N·m of regenerative braking torque, handling much of the braking load — except, of  course, when the EV/PHEV battery is at 100% state of charge.

Simko’s engineers developed an in‑house brake rotor and caliper to produce an assembly that’s 3X lighter than comparable units, contributing to a drive unit power density exceeding 3 kW/kg. The only rotating elements in the drive package are the brake disc, motor rotor, and the wheel rim itself.

Where the Rubber Hits the Road

A distinctive feature lies at the interface between rim and motor: five elastomeric bushings isolate vibration from the permanent‑magnet rotor via the wheel lug bolts. This approach mitigates magnet degradation over time due to vibration and reflects rare attention to coupling road irregularities within hub motor designs. Production versions will feature enlarged damping bushings for greater durability and compliance.

Every other mechanical and thermal component, whether it’s brake caliper, suspension mounts, steering arms, stator oil inlets/outlets, and three‑phase electrical interface, mounts directly to the stator.

Simko’s architecture simplifies assembly, reduces weight by eliminating bracketry and high-load components, and enhances reliability by drastically reducing moving parts.

Low Fat, Less Filling

The S‑drive system is fully ambidextrous as far as the corner of the vehicle that this single-inventory component is installed. It’s capable of enabling high steering angles for both two, and all‑wheel, steer configurations, one-upping tank turns with zero-scrub, in-place 180s and 360s possible with a bit of vehicle platform design imagination. Simko’s drive unit supports double‑wishbone, multilink, and leaf‑spring suspensions, provided wheel diameters are 19 inches or larger.

The S-drive’s hubless torque path trims roughly 20 kg per wheel versus comparable center hubs, pretty much compensating for the weight of the axial-flux motor. It also frees up chassis and body design space while delivering the possibility for torque vectoring, all-wheel steering, packaging flexibility, and enhanced vehicle efficiency.

With the zero-net-mass claim of S-drive, if Simko can deliver cost-parity in-wheel motors, it may actually create an inflection point in electric and hybrid vehicle design and packaging. Check out Bill Wong’s video from CES 2026, where Michal Simko, CTO, shares an overview of Simko’s S-drive system. Look for more details from Michal here at Electronic Design in a few weeks.