Building a Locost is a rewarding project that combines the thrill of a lightweight sports car with the satisfaction of DIY fabrication. The suspension is the heart of the car’s handling, and choosing the right parts can make the difference between an enjoyable back-road blaster and a white-knuckle ride. Whether you are starting from a set of plans or modifying an existing build, understanding suspension components and their purpose is critical. This guide covers everything from geometry essentials to specific parts and practical buying advice.
Understanding Locost Suspension Geometry
The Locost is a Lotus Seven replica that uses a simple, space-efficient chassis. Most designs rely on a double wishbone front and live axle rear, though some builders opt for independent rear suspension. Getting the geometry right from the start ensures predictable handling and tire longevity.
Double Wishbone Design
Double wishbone suspension uses two control arms (upper and lower) to locate the wheel. This design allows the engineer to fine-tune camber change, roll center, and anti-dive characteristics. For a Locost, common lower arm lengths and pickup points are specified in popular plans like the Ron Champion or McSorley designs. Sticking to these dimensions simplifies sourcing and alignment later.
Key Dimensions and Setup
Important measurements include the distance between chassis pickup points, the length of the control arms, and the location of the steering rack. The ideal camber curve should keep the tire contact patch flat during cornering. Toe changes should be minimal as the suspension compresses. A small amount of bump steer is acceptable, but excessive toe change will cause nervous handling. Most builders use a string alignment method at home and later fine-tune at a shop.
Essential Suspension Components for Your Locost Build
Now let’s look at the specific parts you’ll need. Quality, weight, and compatibility are top priorities.
Upper and Lower Control Arms
Control arms connect the chassis to the wheel upright. They come in two main types: fabricated steel or welded tube. Steel arms are strong, affordable, and easy to repair. Aluminum arms save unsprung weight but cost more and require careful welding. Many builders source pre-made arms from specialty suppliers that match common chassis plans. Ensure the arm ends have threaded joints for ball joints or rod ends. Polyurethane bushings offer a good balance of compliance and precision.
Coilover Shocks and Springs
Coilovers combine a spring and damper into one unit. For a Locost, typical spring rates range from 200 to 400 lb/in (front) and 150 to 300 lb/in (rear) depending on engine weight and intended use. Adjustable dampers allow tuning for street or track use. Look for units with threaded bodies for ride height adjustment. Budget-friendly options from brands like QA1 or Speedway Motors work well. Avoid cheap no-name units as they often fail prematurely.
Spindles and Hubs
The spindle holds the wheel bearing and attaches to the control arms. Many builders use custom spindles machined from billet steel or aluminum. Alternatively, modify spindles from a small car like a Toyota Corolla or Ford Escort. The hub must match the wheel bolt pattern (commonly 4x100 or 4x4.5). Wheel bearings should be sealed or greasable. Hub strength is critical—do not reuse worn parts from unknown sources.
Anti-Roll Bars (Sway Bars)
An anti-roll bar reduces body roll during cornering. For a Locost, a front bar is common; a rear bar is optional. The bar connects the lower control arms to the chassis via links. Bar diameter and lever arm length determine stiffness. A 5/8-inch or 3/4-inch solid bar is a typical starting point. Adjustable drop links let you fine-tune the effect. Polyurethane bushings at the chassis mounts reduce friction.
Steering Rack and Steering Arms
The steering rack translates driver input to the wheels. Most Locosts use a manual rack from a small car (e.g., Suzuki Swift or Mini). The rack must be mounted securely with proper bump steer spacing. Steering arms are attached to the spindle—their length affects steering feel and Ackerman geometry. Use the rack manufacturer’s recommended tie rod ends and ensure correct thread engagement.
Choosing the Right Parts: Options and Considerations
With so many suppliers and DIY routes, how do you decide?
Buying Pre-Made vs. Fabricating Your Own
Pre-made suspension parts save time and ensure accuracy. Many companies offer complete kits for popular Locost variants. These kits include matched control arms, coilovers, hubs, and hardware. Fabricating your own parts requires welding skills, a tube bender, and precise measuring. It is cheaper but more time-consuming. For a first build, a pre-made suspension kit is highly recommended to avoid geometry mistakes.
Materials: Steel vs. Aluminum
Steel is the default choice for budget builds. It is strong, easy to weld, and heavy. Aluminum lightens the car but requires special welding techniques (TIG) and costs more. For control arms, consider aluminum if you are chasing performance over weight. For hubs and spindles, steel is safer due to higher fatigue strength.
Sourcing Parts: What to Look For
Specialty retailers for hot rods, circle track, and kit cars carry many compatible parts. Look for components specifically designed for lightweight sports cars. Check that dimensions match your chassis plans—especially arm length and bushing width. Reading forums for builder feedback can help avoid poor-quality items. Always buy a brand with a return policy and clear specifications.
Setting a Realistic Budget
A complete Locost suspension can cost anywhere from $800 to $3,000 depending on quality. A budget build: $800 for control arms (fabricated yourself), $500 for coilovers, $300 for spindles/hubs, $200 for steering rack, $100 for anti-roll bar. A premium build with adjustable dampers and aluminum arms can exceed $3,000. Allocate enough for alignment equipment and a few extra parts.
Installation Tips and Common Pitfalls
Even with the best parts, poor installation ruins performance.
Proper Alignment and Corner Weighting
After assembly, get the car aligned by a shop experienced with race cars. Set camber, caster, and toe per your design. Corner weighing (scales under each wheel) ensures even weight distribution. Adjust ride height to achieve desired rake and clearance.
Avoiding Clearance Issues
Check that control arms do not contact the chassis at full bump or droop. Wheel wells must clear tires at full lock. Measure steering arm clearance to the chassis. It is easier to modify during assembly than after painting.
Upgrading Bushings for Better Feel
Stock rubber bushings have too much compliance for a Locost. Replace them with polyurethane or spherical bearings. Spherical bearings (rod ends) give the stiffest feel but transmit noise. Polyurethane is a good compromise for a road car.
Final Recommendations for a Successful Locost Suspension
Building a Locost suspension is a blend of engineering knowledge and hands-on work. Start by thoroughly studying your chassis plans. Buy pre-made control arms and a matched coilover kit from a reputable supplier. Use steel for spindles and hubs unless you have experience with aluminum fabrication. Invest in a quality steering rack and replace all bushings with polyurethane. Do not shortcut on alignment—a few hundred dollars spent on a professional setup transforms the car’s behavior. With careful part selection and installation, your Locost will handle like a true sports car, delivering miles of smiles on every drive.