Scrub Radius Calculator

Historical Background

The concept of scrub radius has been crucial in automotive engineering for many years. It refers to the distance between the center of the tire's contact patch on the road and where the steering axis line meets the ground. Scrub radius affects steering feel, handling, and stability, making it an important factor in vehicle design and customization. As vehicle designs evolved, especially with modern suspension and steering systems, accurately calculating the scrub radius became essential for optimal performance.

Calculation Formula

The scrub radius can be calculated using the following formula:

\[ \text{Scrub Radius} = \text{Wheel Offset} + \left(\frac{\text{Tire Diameter}}{2} \times \tan(\text{Steering Axis Inclination})\right) \]

• Wheel Offset: The distance between the wheel's mounting surface and its centerline, measured in millimeters.
• Tire Diameter: The overall diameter of the tire, measured in millimeters.
• Steering Axis Inclination: The angle between the steering axis and the vertical, measured in degrees.

Example Calculation

If a vehicle has a wheel offset of 40 mm, a steering axis inclination of 8 degrees, and a tire diameter of 600 mm, the scrub radius is calculated as:

\[ \text{Scrub Radius} = 40 + \left(\frac{600}{2} \times \tan(8^\circ)\right) \approx 40 + (300 \times 0.1405) \approx 40 + 42.15 = 82.15 \text{ mm} \]

Importance and Usage Scenarios

The scrub radius is a key parameter in vehicle dynamics, affecting how the car steers and handles on different road surfaces. A positive scrub radius can enhance steering feedback but may lead to torque steer in front-wheel-drive cars. A negative scrub radius is often used in modern vehicles with ABS and traction control systems to improve stability during braking. Understanding the scrub radius helps automotive engineers and car enthusiasts modify vehicles for optimal performance, handling, and safety.

Common FAQs

1. What is a positive scrub radius?

   • A positive scrub radius occurs when the tire contact patch is outside the steering axis line. It often results in a more responsive steering feel but can lead to torque steer.

2. How does changing wheel offset affect scrub radius?

   • Increasing the wheel offset moves the wheel outward, increasing the scrub radius. Decreasing the offset reduces the scrub radius, potentially resulting in a negative scrub radius if it becomes smaller than the steering axis line.

3. Why is scrub radius important in vehicle dynamics?

   • Scrub radius affects steering feel, road feedback, and stability during braking. It also plays a role in how the car reacts to different forces, such as bumps and torque from acceleration.

This calculator aids automotive enthusiasts and engineers in understanding and adjusting scrub radius, facilitating safer and more enjoyable driving experiences.