Good day everyone,

I have designed the suspension system of an 240 kg (without driver), 80 kW electric race car. The vehicle has been developed with a focus on maximizing maneuverability in tight spaces.

I started the design process by determining the placement of the vehicle’s components. By positioning the motor, battery, controllers, wiring, differential, pedals, and finally the driver(s), I calculated the approximate center of gravity (which was later refined through adjustments).

Next, using sketch work and a suspension analysis program, I determined the suspension hardpoints by testing various parameters such as static camber, camber gain, toe, bump steer, Ackermann, caster, caster trail, kingpin inclination, scrub radius, and the instant centers of the wishbones in front/side/top views, as well as anti-dive/lift/squat geometries. These were analyzed under roll/pitch/heave motions with different ride height, camber, and toe settings.

Although placing the steering rack in front of the wheel axis increased the vehicle’s moment of inertia, it subjected the outer wheel’s tierod to tensile loading during cornering, which helps prevent bending and improves steering feel. Moreover, compared to a rear-mounted steering rack, this layout reduces the angular deflection of the double universal joint on the steering shaft, lowering friction and making steering smoother.

Due to accessibility and budget constraints, I had to use gas-charged bicycle shock absorbers. Therefore, I aimed to maximize the effective use of the shock’s stroke range. To achieve this, I designed a bell crank system that compresses the shock from both sides, ensuring a linear motion ratio across different ride heights. This system also lowers the center of gravity compared to conventional pushrod systems with top-mounted shocks, and the gas shocks are lighter than coil springs. Since the vehicle does not have aerodynamic wings, an anti-roll bar was deemed unnecessary. Nitrogen will be charged into the shocks to prevent changes in stiffness and height caused by temperature rise.

After determining the hardpoints, I proceeded to design the control arms, tierods, pushrods, brackets, bell crank, upright, and hub. Throughout the design phase, manufacturability, lightness, rigidity, adjustability, and ease of maintenance were prioritized. The loads on each component were calculated and optimized through FEA analysis.

While designing the upright, I ensured it could be manufactured on a 3-axis CNC milling machine and allow camber adjustment. I maximized suspension performance by efficiently utilizing the space inside the wheel.

When designing the hubs, I decided to use a floatless brake disc system. The reason was the disc’s ability to self-center with the caliper and its easy removability. Since a 4 mm thick disc was sufficient, any misalignment could cause uneven pad pressure and disc warping, posing a safety risk. The disc’s floater was fixed to the hub via wheel studs, meaning the studs secured both the wheel and the brake disc simultaneously. This design eliminated the need for additional mounting interfaces on the hub, simplifying manufacturing and reducing wheel offset. Consequently, a smaller KPI angle could be used while maintaining the same scrub radius. This allowed for the same camber gain during cornering with reduced caster, softening the steering. Additionally, since the in-wheel carrier system’s center of gravity moved closer to the KPI axis, moment forces due to inertia were reduced.

Wishing everyone productive work and success.