Complete Guide to Formula SAE Suspension Parts: Design, Selection, and Tuning

Designing and building the suspension system for a Formula SAE car is one of the most critical engineering challenges you'll face. The suspension directly affects handling, tire grip, ride quality, and overall vehicle dynamics. Choosing the right Formula SAE suspension parts involves balancing weight, stiffness, adjustability, and cost. This guide covers the key components you need to understand, from uprights to anti-roll bars, along with practical design and selection advice for student teams.

Understanding the Basics of FSAE Suspension

Formula SAE suspension systems are typically double wishbone setups, chosen for their tunability and performance. The main goals are to maximize tire contact patch, control roll, pitch, and dive, and provide consistent geometry throughout suspension travel. Key parameters include wheel rates, motion ratios, camber gain, and scrub radius. All these are influenced by the physical parts you select.

Double Wishbone Geometry

Most FSAE teams use an unequal-length double wishbone arrangement. The upper and lower control arms (wishbones) connect the chassis to the upright. You can adjust the arm lengths and pivot points to control camber, caster, and toe curves. For parts, you'll need rod ends, spherical bearings, or heim joints at the chassis and upright ends. Commonly used materials include 4130 chromoly steel for strength or 6061 aluminum for weight savings, though aluminum requires larger diameters to avoid flex.

Uprights and Hubs

The upright (or knuckle) connects the suspension arms to the wheel hub and brake caliper. FSAE uprights are often CNC-machined from 6061-T6 aluminum or billet 7075-T6 for higher strength. Some teams use steel uprights for welded attachments. Key considerations: weight, stiffness, bearing fits, and mounting points for brake calipers and tie rods. You can buy pre-designed uprights from specialist suppliers or machine your own. Ensure proper spindle size (commonly 25mm or 1 inch) and bearing selection (typically double-row angular contact or tapered roller bearings). Hub and bearing assemblies are critical for durability and low friction.

Essential Formula SAE Suspension Parts

Pushrods and Pullrods

Most FSAE cars use a pushrod suspension, where a rod connects the lower control arm to a rocker arm on the chassis. Pushrods are usually 6061 aluminum tubing or 4130 steel rod with spherical ends. They experience compressive loads, so buckling strength is a design check. For adjustability, you can use turnbuckle-style pushrods with threaded ends. Pullrod systems are less common but can lower the center of gravity; they require tensile-only loading. Both types need high-quality rod ends to minimize friction and ensure accurate force transfer.

Rocker Arms and Bellcranks

Rocker arms (bellcranks) translate pushrod motion to the damper. They provide a motion ratio that multiplies wheel movement to damper displacement. Typical motion ratios range from 0.5 to 0.8 for the front and rear. Rocker arms are often machined from 7075 aluminum or sheet metal (laser cut) with CAD-optimized shapes. They pivot on bearings (e.g., needle or ball bearings) attached to a chassis-mounted shaft. The geometry determines the spring and damping rates at the wheel. You can buy adjustable rockers that allow you to change the motion ratio during testing.

Dampers (Shocks) and Springs

Dampers are perhaps the most performance-critical part. Most FSAE teams use coil-over shock absorbers, either from automotive racing suppliers (e.g., Öhlins, Penske, JRi) or custom-built monotube dampers. Key specs: length (typically 6–8 inches stroke), reservoir type (piggyback or remote), adjustability (bump and rebound clickers), and spring rate (350–600 lb/in). Coil springs can be 2.25-inch or 2.5-inch ID, commonly made from chrome silicon steel. You'll need spring perches and adjusters for ride height tuning. For spring rates, start with a target wheel rate and calculate using the motion ratio squared: Wheel Rate = Spring Rate * (Motion Ratio)^2.

Anti-Roll Bars (Sway Bars)

Anti-roll bars reduce body roll and tune understeer/oversteer balance. FSAE bars are typically 4130 steel tubing with arm lengths and blade-style ends. They attach to the lower control arm or pushrod via drop links. The bar size (diameter and wall thickness) and arm length determine stiffness. Some teams use blade-style bars that allow stiffness adjustment by rotating the bar. Commercially available anti-roll bars for FSAE are rare; many teams fabricate their own. When designing, consider the bar's torsional stiffness and its effect on roll moment distribution.

Materials and Manufacturing Considerations

Lightweight is paramount, but so is reliability. Common materials for suspension parts:

• Aluminum 6061-T6 and 7075-T6 for uprights, arms, rockers, and brackets. 7075 is stronger but heavier; 6061 is easier to machine.
• Steel 4130 chromoly for wishbones, pushrods, and anti-roll bars – weldable and strong.
• Carbon fiber for pushrods or control arms is possible but expensive and requires careful design to avoid fatigue.
• Titanium is used in top-tier teams for fasteners or small parts due to weight savings.

Manufacturing methods: CNC machining for complex parts like uprights and rockers, waterjet or laser cutting for brackets, tube bending and welding for arms. Always consider stress concentrations, especially around welding joints and mounting holes.

Sourcing and Buying Parts

Many parts are available from racing suppliers. For rod ends, brands like Aurora, FK, and QA1 are common. Springs: Hyperco, Eibach, or Swift. Dampers: you can purchase FSAE-specific shocks from companies like Öhlins USA or Penske Racing Shocks – they often have student discounts. Uprights and hubs can be bought from Formula SAE part specialists or designed in-house. Keep in mind lead times and cost; budget a significant portion for suspension. It's often better to invest in high-quality dampers and rod ends than to save money on unproven parts.

Tuning and Setup Tips

Once you have parts assembled, proper setup is crucial. Start with ride heights and corner weights using a scales at competition. Set static camber (typically 0.5–2 degrees negative), caster (4–6 degrees), and toe (1/16–1/8 inch toe-out front, toe-in rear). Damping adjustment: begin with recommended settings from the damper manufacturer, then tune for track conditions. Use accelerometer data or driver feedback to adjust anti-roll bar stiffness and spring rates. Always record changes.

Final Recommendations

For teams new to Formula SAE or limited by budget, focus on reliability and adjustability. Purchase proven dampers and rod ends, fabricate your own arms and rockers from 4130 steel or 6061 aluminum, and use a well-designed double wishbone geometry from an established template. Avoid exotic materials unless you have experience. For advanced teams, consider carbon pushrods, custom billet uprights, and a fully adjustable anti-roll bar. No matter what, test early and iterate. The best suspension parts are those that work together with proper design and tuning.

Remember, the suspension is a system – each part affects others. Invest time in simulation and on-track testing. Good luck building your FSAE car!