RockShox Spring Rate Calculator
Mastering Your RockShox Coil Setup: The Ultimate Guide
Transitioning to a coil shock like the RockShox Super Deluxe Coil or Vivid Coil offers unparalleled small-bump sensitivity and consistency on long descents. Unlike air shocks where you simply adjust a pump, coil shocks require selecting the specific physical spring rate (measured in lbs/in) that matches your weight and bike geometry.
How the RockShox Spring Rate is Calculated
This calculator uses the physics of leverage ratios and rider weight distribution to find your ideal starting point. The formula accounts for:
- Leverage Ratio: Calculated by dividing your frame's total travel by the shock's stroke length.
- Weight Distribution: Most mountain bikes carry approximately 65% to 70% of the rider's weight on the rear wheel when in a neutral descending position.
- Target Sag: Usually 25-30% for Enduro and Downhill bikes.
Example Calculation
If you weigh 180 lbs, your bike has 160mm of travel with a 65mm stroke shock, and you want 30% sag:
| Step | Metric | Value |
|---|---|---|
| 1 | Leverage Ratio | 160 / 65 = 2.46 |
| 2 | Force on Shock at Sag | 180 lbs * 0.70 (bias) * 2.46 = 310 lbs |
| 3 | Shock Compression at Sag | 65mm * 0.30 = 19.5mm (0.76 inches) |
| 4 | Required Spring Rate | 310 / 0.76 ≈ 400 lbs/in |
Pro Tips for RockShox Coil Setup
1. Between Sizes? If the calculator suggests a 425lb spring but you can only find 400lb or 450lb, consider your riding style. Choose the 450lb (firmer) for big jumps and high speeds, or 400lb (softer) for maximum traction in technical, wet terrain.
2. Preload Limits: RockShox recommends using between 1 and 2 full turns of preload. If you need more than 2 turns to achieve the correct sag, you need a heavier spring rate. If you have zero preload and too little sag, you need a lighter spring.
3. Stroke Clearance: Ensure the spring you buy has a "Spring Stroke" greater than your shock's stroke. For example, a 65mm stroke shock requires a spring rated for at least 65mm (often labeled as 2.5″ or 2.75″ / 65-75mm) to prevent coil bind.