Ride Rate Calculation

by

Vehicle Ride Rate Calculator

Results

Wheel Rate: 0 units

Effective Ride Rate: 0 units

*Note: Units (lb/in or N/mm) match your input units.

function calculateRideRate() { var springRate = parseFloat(document.getElementById('springRate').value); var motionRatio = parseFloat(document.getElementById('motionRatio').value); var tireRate = parseFloat(document.getElementById('tireRate').value); if (isNaN(springRate) || isNaN(motionRatio) || isNaN(tireRate) || motionRatio <= 0) { alert("Please enter valid positive numerical values for all fields."); return; } // Step 1: Calculate Wheel Rate (Kw = Ks * MR^2) var wheelRate = springRate * Math.pow(motionRatio, 2); // Step 2: Calculate Ride Rate (Kr = (Kw * Kt) / (Kw + Kt)) // This treats the wheel rate and tire rate as two springs in series var rideRate = (wheelRate * tireRate) / (wheelRate + tireRate); document.getElementById('wheelRateResult').innerText = wheelRate.toFixed(2); document.getElementById('rideRateResult').innerText = rideRate.toFixed(2); document.getElementById('resultsArea').style.display = 'block'; }

Understanding Ride Rate in Vehicle Dynamics

Ride rate is a critical metric in automotive engineering that defines the effective stiffness of a vehicle's suspension at the contact patch of the tire. Unlike the spring rate, which only measures the stiffness of the coil spring itself, the ride rate accounts for the mechanical leverage of the suspension geometry (motion ratio) and the vertical stiffness of the tire.

How the Ride Rate is Calculated

The calculation involves two primary stages. First, we determine the Wheel Rate. Because the spring is usually mounted somewhere along a control arm rather than directly on the wheel hub, it operates through a lever. This leverage is called the Motion Ratio. The wheel rate is calculated by multiplying the spring rate by the square of the motion ratio.

Second, we must account for the Tire Rate. Since the tire acts as a spring in series with the suspension, the final Ride Rate is always lower than both the wheel rate and the tire rate. It is calculated using the formula for springs in series: (Wheel Rate × Tire Rate) / (Wheel Rate + Tire Rate).

Key Components Defined

  • Spring Rate: The force required to compress a spring by a specific distance (e.g., 500 lbs to compress 1 inch).
  • Motion Ratio: The ratio of spring travel to wheel travel. A ratio of 0.7 means for every 1 inch the wheel moves, the spring moves 0.7 inches.
  • Tire Rate: The vertical stiffness of the tire carcass, which varies based on air pressure and sidewall construction.

Practical Example

Imagine a performance car with the following specs:

  • Spring Rate: 600 lb/in
  • Motion Ratio: 0.8
  • Tire Rate: 1,200 lb/in

Step 1: Wheel Rate = 600 × (0.8 × 0.8) = 384 lb/in.

Step 2: Ride Rate = (384 × 1200) / (384 + 1200) = 460,800 / 1,584 = 290.91 lb/in.

In this example, the actual stiffness felt by the chassis is significantly lower than the 600 lb/in spring installed on the car. This is why professional tuners focus on ride rate rather than just spring rate when balancing a vehicle's handling characteristics.

Why Ride Rate Matters

Determining the ride rate is the first step in calculating a vehicle's Ride Frequency (measured in Hertz). Ride frequency determines the "feel" of the car—whether it feels soft and luxury-oriented (1.0 – 1.5 Hz) or stiff and track-ready (2.0 – 3.0+ Hz). Without knowing the ride rate, it is impossible to accurately predict how the vehicle will react to bumps or weight transfer during cornering.

Leave a Comment