Rear Bump Allowance Given Rear Ride Rate Calculator

Formula Used:

\[ \text{Rear Bump Allowance} = \frac{\text{Rear Outside Wheel Change} \times [g]}{\text{Rear Ride Rate} \times 2} = \frac{\Delta W_{ro} \times [g]}{K_r} \]

Rear Bump Allowance:

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1. What is Rear Bump Allowance?

Rear Bump Allowance refers to the vertical movement of the spring when the vehicle encounters a full bump. It represents the maximum compression the rear suspension system can accommodate during bump conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{Rear Bump Allowance} = \frac{\text{Rear Outside Wheel Change} \times [g]}{\text{Rear Ride Rate}} \]

Where:

\( \text{Rear Outside Wheel Change} (\Delta W_{ro}) \) — Difference in load on rear outside wheel during cornering vs straight path (kg)
\( [g] \) — Gravitational acceleration constant (9.80665 m/s²)
\( \text{Rear Ride Rate} (K_r) \) — Vertical force per unit vertical displacement (N/m)

Explanation: This formula calculates the vertical spring movement by relating the load change during cornering to the suspension's ride rate, using gravitational acceleration as a conversion factor.

3. Importance of Rear Bump Allowance Calculation

Details: Accurate calculation of rear bump allowance is crucial for proper suspension design, ensuring adequate wheel travel, preventing bottoming out, and maintaining vehicle stability and comfort during cornering and bump conditions.

4. Using the Calculator

Tips: Enter Rear Outside Wheel Change in kilograms and Rear Ride Rate in Newtons per meter. Both values must be positive numbers greater than zero for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is Rear Outside Wheel Change?
A: It's the difference between the load on the rear outside wheel during cornering and the load during straight path travel, measured in kilograms.

Q2: What is Rear Ride Rate?
A: Rear Ride Rate is defined as vertical force per unit vertical displacement of the tire ground contact with respect to chassis, measured in Newtons per meter.

Q3: Why is gravitational acceleration used in the formula?
A: Gravitational acceleration converts mass (kg) to force (N) since ride rate is measured in N/m (force per displacement).

Q4: What are typical values for Rear Bump Allowance?
A: Typical values range from 0.02 to 0.15 meters depending on vehicle type and suspension design, with performance vehicles generally having smaller allowances.

Q5: How does this calculation affect vehicle performance?
A: Proper bump allowance ensures the suspension can handle road irregularities without bottoming out, maintaining tire contact with the road and ensuring stable handling characteristics.