.calc-container-main {
max-width: 800px;
margin: 0 auto;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
padding: 20px;
background-color: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.calc-header {
text-align: center;
margin-bottom: 30px;
color: #333;
}
.calc-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.calc-col {
flex: 1;
min-width: 250px;
}
.calc-label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #444;
}
.calc-input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.calc-input:focus {
border-color: #007bff;
outline: none;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #0056b3;
}
.result-box {
margin-top: 30px;
padding: 20px;
background-color: #ffffff;
border: 1px solid #ddd;
border-radius: 6px;
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
color: #666;
}
.result-value {
font-weight: bold;
color: #222;
}
.calc-note {
font-size: 0.9em;
color: #666;
margin-top: 5px;
}
.article-section {
margin-top: 50px;
line-height: 1.6;
color: #333;
}
.article-section h2 {
color: #2c3e50;
margin-top: 30px;
}
.article-section h3 {
color: #34495e;
margin-top: 20px;
}
.article-section p {
margin-bottom: 15px;
}
.article-section ul {
margin-bottom: 15px;
padding-left: 20px;
}
function calculateSuspension() {
// Get input values
var sr = parseFloat(document.getElementById('springRate').value);
var mr = parseFloat(document.getElementById('motionRatio').value);
var w = parseFloat(document.getElementById('cornerWeight').value);
var angle = parseFloat(document.getElementById('springAngle').value);
// Validation
if (isNaN(sr) || isNaN(mr) || isNaN(w)) {
alert("Please enter valid numbers for Spring Rate, Motion Ratio, and Corner Weight.");
return;
}
if (angle === "" || isNaN(angle)) {
angle = 0;
}
// Calculation Logic
// 1. Calculate Angle Correction Factor (Cosine of angle from vertical)
// Convert degrees to radians: rad = deg * (PI/180)
var angleRad = angle * (Math.PI / 180);
var angleCorrection = Math.cos(angleRad); // This is usually squared in the final formula
// 2. Calculate Wheel Rate
// Formula: WR = SR * (Motion Ratio)^2 * (Angle Correction)^2
var wheelRate = sr * (mr * mr) * (angleCorrection * angleCorrection);
// 3. Calculate Natural Frequency (Hz)
// Formula: f = (1 / 2*PI) * sqrt( (Wheel Rate * Gravity) / Weight )
// Gravity constant in inches/sec^2 is approx 386.1
var gravity = 386.1;
var freqHz = (1 / (2 * Math.PI)) * Math.sqrt((wheelRate * gravity) / w);
// 4. Calculate CPM (Cycles Per Minute)
var cpm = freqHz * 60;
// 5. Determine Ride Type
var rideType = "";
if (freqHz = 1.0 && freqHz = 1.5 && freqHz = 2.0 && freqHz < 3.0) {
rideType = "Dedicated Race Car (Non-Aero)";
} else {
rideType = "High Downforce / Formula Car";
}
// Display Results
document.getElementById('resWheelRate').innerText = wheelRate.toFixed(2) + " lbs/in";
document.getElementById('resFreq').innerText = freqHz.toFixed(2) + " Hz";
document.getElementById('resCPM').innerText = cpm.toFixed(1) + " cpm";
document.getElementById('resType').innerText = rideType;
document.getElementById('result').style.display = "block";
}
Suspension Rate & Frequency Calculator
Calculate Wheel Rate and Suspension Natural Frequency based on Spring Rate and Motion Ratio.
The rating of the coil spring itself.
Leverage ratio of the control arm (Wheel travel / Spring travel).
Unsprung mass subtracted from total corner weight.
Angle of the spring from vertical (0 = vertical).
Calculation Results
Effective Wheel Rate:
–
Suspension Frequency (Hz):
–
Cycles Per Minute (CPM):
–
Ride Characteristic:
–
Optimizing Vehicle Dynamics: Understanding Suspension Rates
When tuning a vehicle for performance or comfort, simply buying stiffer springs isn't enough. You must calculate the Wheel Rate and the Natural Suspension Frequency to truly understand how the car will behave on the road or track. This Suspension Rate Calculator helps you translate the raw mechanical specifications of your springs into the actual dynamics experienced by the chassis.
Spring Rate vs. Wheel Rate
Many enthusiasts confuse Spring Rate with Wheel Rate.
- Spring Rate: The stiffness of the spring itself, usually measured in lbs/in or kg/mm. This is the number printed on the box.
- Wheel Rate: The effective stiffness measured at the wheel center. Because springs are often mounted inward on a control arm (not directly above the wheel), the leverage effect reduces the effective rate.
The Motion Ratio is the critical multiplier here. If your spring is mounted halfway down the control arm (0.5 motion ratio), the spring has much less leverage against the wheel. In fact, the relationship is squared. A 0.5 motion ratio means your Wheel Rate is only 25% of your Spring Rate ($0.5^2 = 0.25$).
Why Natural Frequency (Hz) Matters
Suspension Natural Frequency is the rate at which the suspension oscillates freely after a bump. It is measured in Hertz (Hz) or Cycles Per Minute (CPM). This metric is the gold standard for comparing suspension setups across different vehicles because it normalizes stiffness relative to the vehicle's weight.
- 1.0 – 1.5 Hz: Typical passenger cars and sports sedans. Optimized for comfort and handling bumps.
- 1.5 – 2.0 Hz: Performance street cars and track-day vehicles. Reduced body roll but harsher ride.
- 2.0 – 3.0+ Hz: Dedicated race cars. Very stiff to support aerodynamic loads and slick tires.
How to Use This Calculator
- Spring Rate: Enter the rate of your spring in lbs/in.
- Motion Ratio: Enter the installation ratio. For MacPherson struts, this is usually close to 0.9 – 1.0. For wishbone suspension, measure the distance from the pivot to the spring vs. pivot to the ball joint.
- Corner Weight: Enter the sprung weight on that specific corner. (Total car weight / 4 is a rough estimate, but corner balancing scales are better).
- Spring Angle: If the shock/spring is mounted at an angle, it loses efficiency. Enter the degrees off-vertical to correct for this.