In the context of RC car suspension geometry, adjusting the upper arm mounting location, while keeping its length fixed, significantly alters the suspension kinematics. This adjustment, particularly moving the upper arm's inboard or outboard pivot points, affects the camber gain and roll center, thereby influencing the handling dynamics. Here's an analysis using engineering terms:
- Camber Gain and Roll Center Dynamics:Camber Gain: This refers to the rate at which the camber angle of the wheel changes relative to the vertical travel of the suspension. It's a key factor in determining how the tire maintains contact with the driving surface, especially in cornering.
Roll Center: The roll center is an imaginary point around which the car's chassis rolls during cornering. It's a critical aspect of suspension design, influencing the vehicle's roll stiffness and handling balance.
- Upper Arm Mounting Adjustments:Moving Inboard: Relocating the upper arm's mounting point further inboard (towards the centerline of the vehicle) while keeping the arm length constant, will increase the angular change of the arm relative to the chassis during suspension movement. This typically results in a higher camber gain, meaning the wheel camber changes more rapidly with vertical suspension travel. Such a setup can enhance cornering grip due to increased negative camber during body roll, but it may also introduce more dynamic camber changes, potentially leading to less predictable handling at different suspension loads.
Moving Outboard: Conversely, moving the upper arm's mounting point outboard (away from the centerline) reduces the angular change of the arm during suspension movement, leading to lower camber gain. This setup offers more consistent camber angles through the suspension travel, contributing to more predictable handling and tire wear. However, it might reduce the maximum achievable grip in high-speed corners due to less negative camber gain during body roll.
- Impact on Roll Center Height:Adjusting the upper arm's mounting location also affects the roll center height. Moving the mounting point inboard generally raises the roll center, which can reduce body roll and improve roll stiffness. This makes the car more responsive but might reduce mechanical grip on bumpy surfaces. Conversely, moving it outboard lowers the roll center, which can increase body roll but potentially improve mechanical grip on uneven surfaces.
- Engineering Considerations:Suspension Geometry Optimization: The adjustment of the upper arm mounting points must be optimized in the context of the entire suspension geometry, including considerations of kingpin inclination, scrub radius, and other kinematic factors.
Vehicle Dynamics Analysis: A comprehensive analysis using principles of vehicle dynamics is essential to predict how these changes will affect handling. This includes evaluating the effects on load transfer, tire contact patch optimization, and transient response under various driving conditions.
Testing and Validation: Real-world testing is crucial to validate theoretical predictions. Changes in suspension geometry should be tested under controlled conditions to assess their impact on handling characteristics, lap times, and driver feedback.
In summary, adjusting the mounting location of the upper arm in relation to the lower arm, while maintaining its length, alters the suspension's camber gain and roll center characteristics. Moving the mounting point inboard increases camber gain and raises the roll center, potentially enhancing cornering grip at the expense of predictability. Moving it outboard reduces camber gain and lowers the roll center, leading to more consistent handling but possibly at the cost of maximum cornering grip. These adjustments should be integrated into a holistic suspension design and validated through empirical testing to optimize the vehicle's handling dynamics.