Stock Car (Scratch-Built/Late Model)

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Stock Car (Scratch-built /Late Model)

The scratch-built stock car (Sometimes referred to as a "Late model", "NASCAR" or just "Stock Car") is a purpose-built race car which has bodywork to make it appear similar to a stock production car, but in fact uses a tube chassis instead of the production unibody chassis. Stock cars got their name originally from the fact they were built from stock production base vehicles.

The scratch-built stock car is characterized by a tube frame chassis with a high horsepower engine mounted at the front which drives the two rear wheels. The suspension design and chassis place the car very close to the ground for the lowest possible CG (Center of gravity). The chassis is covered with formed steel bodywork or FRP composites that gives the shape of the production car the builder wants to represent.

Variations of the stock car concept are used on dirt and paved ovals, with the dirt versions sharing characteristics with Sprint and Midget racing.

Outside the USA the term "Stock Car" is often used when referring to truly stock production cars. In our race car types, the "Stock Car (Production-based)", "GT" and "Touring" are more appropriate starting points for these types. In the UK, the term Stock Car is also used to refer to a "Sprint Car"-like race car.

Racing events have been held on oval and road course circuits in the Americas, Europe, Australia and New Zealand.

Power and Weight Stats
Horsepower (Typical Range) 450-725
Race Weight (Typical Range) 1362-1498 kg
3000-3300 lb

Design and Construction

Race Car Models of This Type

NASCAR, ARCA, ACTC (Argentinean), StockCar Brazil

Build Your Own Scratch-built Stock Car

Knowledge Level

Due to the scratch-built nature of this type of race car, you should be knowledgeable in handling, chassis, suspension, powertrain, aerodynamic and safety design. These six major areas of the car design work as an integrated unit and the designer must have an understanding of how changes to one area affect the others. Much of the design work is iterative, meaning re-designing areas based on new changes to another area. After the iterations are completed, the design will be complete and optimized.

Stock cars are primarily oval racing cars, and as such they rely heavily upon fine tuning their handling through chassis, suspension and aerodynamics. Having an especially strong understanding in these areas can be helpful.

Design Challenges

Weight Distribution: Typically the front will be heavier in front/rear weight distribution due to the front-engine configuration. Weight distribution that is almost balanced Front/Rear is desirable, so positioning components rearward to counter engine weight will help achieve this. Static left/right weight distribution may be adjusted depending on the type of circuit (Oval versus road course) via positioning of internal components such as the battery, oil tank, oil cooler and fuel cell.

Suspension: Maximizing the contact patch of the tires with good suspension geometry is of key importance. The suspension design should also include spring wedge adjustments at the rear to assist in weight transfer.

Suspension, wheel and tire weights (Unsprung weight) affect the compliance of the suspension, which in turn affects handling, so keeping all these components as light as possible is an advantage. Springs and dampers (shock absorber) must be matched to the suspension geometry and calculated weight transfer forces to provide useful, tunable performance.

The suspension pickup point locations will impact the chassis structural design.

Chassis: Designing torsional rigidity into the chassis will give predictable handling as the chassis will not twist unduly affecting the suspension performance. Optimizing the chassis to give the highest level of performance to satisfy requirements (torsional rigidity, impact protection, etc.) while minimizing weight will provide a solid platform with the opportunity to distribute ballast weight more favourably.

Powertrain: Weight distribution is heavily impacted by engine position, so placing it as far back as permitted and safe as part of a near balanced weight distribution is preferred. Intake, Cooling and exhaust need to be considered in relation to chassis design, bodywork and aerodynamics.

Aerodynamic: NASCAR-style stock cars use a front air dam and rear spoiler are used to generate downforce while other series use a rear wing. Using a single airflow to perform two functions (i.e. To provide downforce and cooling) can increase the efficiency over two separate flows. As top speed is often over 100 mph (160 km/h) in asphalt racing, careful attention to the aerodynamic cleanness of the car can yield useful gains.

Safety: The chassis design should seek to provide good protection for the driver through a substantial crash/rollover safety cell with racing seat and racing harness and padding around the driver as needed. Fuel safety is provided via a fuel safety cell while fire protection is provided with an integrated chassis firewall. Front/side/rear impact protection is usually provided by multi-tube structures integral to the chassis.

If you intend to race under a sanctioning body, always read and understand the regulations of your chosen racing class before designing or building any race vehicle.

Design Resources

Learn the basics about race cars and race car design from our free online knowledge series

Download our free race car design aids to assist you designing your race vehicle.

In-depth books and learning resources we recommend for scratch-built stock car design.

Join our forum to ask and find answers to your scratch-built stock car design/construction questions.

Construction Challenges

Ensuring the chassis is dimensionally accurate and straight is important as flaws in the structure will create handling issues via misaligned suspension. The use of a solid, flat and level build space is important. Jigs are often used in this case to ensure that structural tubing stays in alignment during welding/brazing.

The builder should have solid joining and metal working knowledge and skills when fabricating the chassis/rollcage/suspension. While mild steel (1018/1020) is very forgiving, some metals are best welded using a specific method (mig/tig) and some require heat treatments before and following welding to restore their toughness and strength.

Having sufficient space for the chassis and bodywork construction is important, as a cramped workshop can be difficult to work in.

The tools to fabricate the chassis and bodywork can add considerably to the cost of your project if you don't already have a workshop, but borrowing or renting items is also an option.

Build Costs

Many parts for a scratch-built stock car can be purchased as racing components via stock car racing suppliers. Production aftermarket companies may offer more economically priced, yet just as capable components, so it pays to understand the materials and structure of components.

The ultimate cost depends on the need for dedicated racing components and the overall level of competitiveness in the series you wish to participate in. Chassis fabrication costs will vary depending on the series, and in some cases, the chassis can be purchased pre-fabricated which will save build effort.

Build Effort

As the car is scratch-built, there will be significant effort in design and construction. There is however, an equally great satisfaction and sense of accomplishment at being one of the few people in the world who have built their own race truck from the ground up! If regulations for your series are very restrictive, pre-fabricated components like the chassis can reduce effort. Study/replication of existing car designs can also short-path your design and construction.

Racing Cost

Tires and fuel probably form the single largest consumable expense along with engine rebuilds and body repairs.

Transportation and Support Equipment

Trailering required.

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