Spring Rate Required For Coilover Given Desired Droop And Motion Ratio Calculator

Formula Used:

\[ k = \frac{W_{cs} \times g}{M.R. \times W.T. \times \cos(\theta_s)} \]

Corner Sprung Mass of Vehicle:

Acceleration due to Gravity:

m/s²

Motion Ratio in Suspension:

Wheel Travel:

Angle of Spring/Shock Absorber from Vertical:

rad

Stiffness of Spring:

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1. What is Spring Rate Calculation?

Spring rate calculation determines the required stiffness of a coilover spring based on vehicle parameters and suspension geometry. It ensures optimal suspension performance and handling characteristics for racing applications.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ k = \frac{W_{cs} \times g}{M.R. \times W.T. \times \cos(\theta_s)} \]

Where:

\( k \) — Stiffness of Spring (N/m)
\( W_{cs} \) — Corner Sprung Mass of Vehicle (kg)
\( g \) — Acceleration due to Gravity (m/s²)
\( M.R. \) — Motion Ratio in Suspension
\( W.T. \) — Wheel Travel (m)
\( \theta_s \) — Angle of Spring/Shock Absorber from Vertical (rad)

Explanation: The formula calculates the required spring stiffness by considering the vehicle's corner mass, gravitational force, suspension motion ratio, wheel travel distance, and spring angle from vertical.

3. Importance of Spring Rate Calculation

Details: Proper spring rate calculation is crucial for optimal suspension performance, ensuring the vehicle maintains proper ride height, handles predictably, and maximizes tire contact with the racing surface.

4. Using the Calculator

Tips: Enter corner sprung mass in kg, acceleration due to gravity in m/s² (typically 9.8), motion ratio (dimensionless), wheel travel in meters, and spring angle from vertical in radians. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: Why is spring angle important in the calculation?
A: The spring angle affects the effective spring rate as the cosine function accounts for the reduced vertical force component when the spring is not perfectly vertical.

Q2: What is motion ratio and how is it determined?
A: Motion ratio is the ratio of spring displacement to wheel displacement. It's determined by the suspension geometry and typically ranges from 0.5 to 1.0 for most suspension designs.

Q3: How does wheel travel affect spring rate?
A: Greater wheel travel requires a softer spring to achieve the same ride frequency, while limited travel requires a stiffer spring to prevent bottoming out.

Q4: Can this calculator be used for both front and rear suspensions?
A: Yes, but you need to use the appropriate corner mass, motion ratio, and geometry values for each suspension corner separately.

Q5: What are typical spring rate values for racing applications?
A: Spring rates vary widely depending on vehicle weight, suspension type, and racing discipline, but typically range from 100-1000 N/m for lighter vehicles to 200-2000 N/m for heavier racing cars.