Intro to Racecar Engineering: 01 Getting Started

Summary

In this informative lecture, Robert 'Smitty' Smith, a mechanical engineering advisor at UCI, introduces a series of hands-on demonstrations on race car engineering. He discusses essential design principles for FSAE race cars, starting with tire selection, vehicle geometry, suspension design, and ergonomics. Key topics include optimizing tire contact patches, wheelbase, camber, roll center, and steering geometry, while emphasizing the importance of considering driver comfort and visibility. The lecture provides practical guidance for students designing their own race cars, with a focus on achieving performance, safety, and functionality in autocross events.

Takeaways

• 😀 Select the tire diameter first, as it influences other design parameters such as wheelbase, suspension geometry, and overall vehicle performance.
• 😀 Tire diameter impacts temperature regulation and performance, with smaller tires (e.g., 10-inch) heating up more efficiently than larger ones (e.g., 13-inch).
• 😀 Keep in mind that a 10-inch tire, while better for heat and weight, complicates packaging of components like brakes, uprights, and steering linkages.
• 😀 The ideal wheelbase for FSAE cars should be around 60 inches, providing agility for autocross events, which demand nimbleness rather than high-speed stability.
• 😀 Track width should be approximately 75-80% of the wheelbase for optimal vehicle stability and performance in autocross environments.
• 😀 When designing suspension geometry, aim for a lower arm length that promotes rising camber, which helps keep the tire contact patch flat during cornering.
• 😀 Center of gravity (CoG) must be kept low and centered to pass the 60-degree tilt test, ensuring vehicle stability during cornering loads.
• 😀 Roll center height should be lower in the front and higher in the rear, with the rear height no more than 30% of the CoG height for balanced handling.
• 😀 Steering geometry should prioritize full Ackermann, or as close as possible, for better handling and turning performance in tight autocross conditions.
• 😀 Consider ergonomic design for the driver to ensure comfort and visibility. Proper driver ergonomics are often neglected in FSAE designs, yet are crucial for performance.

Q & A

What is the most important initial factor when designing a race car?

The most important initial factor is selecting the tire. The tire diameter, compound, and width are critical, as they directly influence the overall car performance and handling.

Why is a 10-inch tire preferred over a 13-inch tire in FSAE cars?

A 10-inch tire is preferred because it heats up more quickly, offering better performance at lower speeds. It is also lighter, which is a significant consideration in FSAE design, where weight reduction is crucial.

What is the role of camber in race car design?

Camber helps keep the tire's contact patch flat on the ground during cornering. The target camber angle is determined by the tire manufacturer, but an additional 1.5 degrees of camber adjustment is often needed due to suspension compliance.

What is the ideal wheelbase for an FSAE car and why?

The ideal wheelbase is typically around 60 inches, as a shorter wheelbase increases the car's agility, which is crucial for autocross events that require nimbleness and quick maneuverability.

How is the track width related to the wheelbase in FSAE design?

The track width should be approximately 75-80% of the wheelbase. This proportion provides an excellent balance between stability and maneuverability, especially in autocross conditions.

What does the vertical center of gravity (CG) affect in an FSAE car?

The vertical center of gravity affects the car’s performance in the 60° tilt test, which simulates high cornering loads. A lower CG ensures that the car is stable during cornering and doesn't tip over easily.

Why is the rear roll center of an FSAE car typically higher than the front?

Having a higher rear roll center than the front helps the car roll more predictably in corners. This setup improves the car's handling by reducing the likelihood of unwanted jacking effects that could destabilize the vehicle.

What is jacking effect and why is it undesirable in FSAE cars?

Jacking effect occurs when the car’s center of gravity rises during a roll, causing the car to become unstable. This is undesirable because it can lead to the car flipping or rolling over, particularly under heavy cornering forces.

What steering geometry is recommended for autocross in FSAE cars?

For autocross, full Ackermann geometry is recommended, or slightly less than full Ackermann. This provides the best balance for tight cornering, which is typical in autocross events.

How can bump steer be minimized in an FSAE car?

Bump steer, which occurs when suspension movement affects steering direction, should be minimized by carefully designing the suspension geometry. The ideal situation is to achieve zero bump steer, though this is challenging in practice.