Enter Shock and Rider Details
Example Data Table
| Rider + Gear | Travel | Stroke | Target Sag | Ride Feel | Estimated Spring |
|---|---|---|---|---|---|
| 165 lb | 150 mm | 60 mm | 30% | Balanced | 425 lb/in |
| 185 lb | 160 mm | 65 mm | 30% | Firm | 475 lb/in |
| 205 lb | 170 mm | 65 mm | 28% | Race | 575 lb/in |
Formula Used
This calculator estimates coil spring rate from rider load, target sag, and suspension leverage.
First it calculates leverage ratio:
Leverage Ratio = Rear Wheel Travel / Shock Stroke.
Then it calculates target wheel sag:
Wheel Sag = Travel × Sag Percentage.
The main spring estimate is:
Spring Rate = Rear Load × Leverage Ratio² / Wheel Sag.
The calculator then adjusts that number with ride feel and progression factors.
A plush setup lowers the estimate slightly.
A race setup raises it for more support.
Current spring sag is estimated with:
Wheel Sag = ((Rear Load × Leverage Ratio / Spring Rate) - Preload) × Leverage Ratio.
This helps show whether your current coil is close, too soft, or too firm.
How to Use This Calculator
Enter your rider weight and the weight of your riding gear. Choose pounds or kilograms. Add rear wheel travel and shock stroke from your frame and shock setup. Pick a sag target. Trail and enduro riders often start near 30 percent. More support usually means less sag.
Select a ride feel. Plush gives comfort and grip. Balanced suits most riding. Firm adds mid-stroke support. Race support favors speed, jumps, and hard impacts. Enter your current spring rate to compare your existing coil. Add preload turns to estimate actual sag.
Fox DHX2 Spring Setup Guide
Why Spring Rate Matters
A coil shock depends on the correct spring before damping can work well. The spring holds the rider at the right ride height. It also controls how much travel remains for bumps, drops, and compressions. If the rate is too soft, the bike can sit deep in travel. Pedaling may feel heavy. Corner support can fade. Bottom outs may become common. If the rate is too firm, the bike can ride high. Grip may drop on loose ground. Small bumps can feel sharp. The rear wheel may skip instead of tracking.
Using Sag as the Starting Point
Sag is the amount of travel used when the rider sits on the bike in normal riding kit. It is the best first check because it includes body weight, gear, frame leverage, and shock stroke. Many aggressive trail and enduro bikes start near thirty percent sag. Downhill riders may choose a little less for more support. Riders who want traction may choose a little more. Always measure sag while standing in a natural riding stance.
Preload and Spring Choice
Preload should fine tune sag. It should not replace the correct coil. A small amount of preload keeps the spring seated and can sharpen support. Too much preload may reduce grip and make the first part of travel harsh. If the calculator shows that large preload is needed, choose a stiffer spring. If sag is too low with almost no preload, choose a softer spring.
Final Trail Check
Use the result as a setup estimate. Then test the bike on familiar terrain. Check sag again after a short ride. Watch full travel use. Listen for hard bottom outs. Adjust rebound and compression only after the spring feels close. A correct coil makes every other adjustment easier, clearer, and more repeatable.
FAQs
1. What spring rate should I use for a DHX2 shock?
Use the rate that gives your target sag with light preload. The correct number depends on rider weight, gear, rear travel, shock stroke, leverage ratio, and riding style.
2. Is 30 percent sag good for a coil shock?
Thirty percent is a common starting point for trail and enduro riding. Some riders prefer less sag for support, while others prefer more sag for traction.
3. Should I use preload to fix sag?
Use preload only for fine tuning. If you need lots of preload to reach sag, the spring is probably too soft. Choose a firmer coil instead.
4. What happens if my spring is too soft?
The bike may sit too low, wallow in corners, pedal poorly, and bottom out often. It may feel comfortable first, but support can disappear quickly.
5. What happens if my spring is too firm?
The bike may ride high and feel harsh. Rear grip can suffer because the wheel may not follow rough ground smoothly enough.
6. Why does leverage ratio affect spring rate?
Leverage ratio shows how much the wheel moves compared with the shock. Higher leverage needs a firmer spring because wheel force is multiplied.
7. Should I include riding gear weight?
Yes. Helmet, shoes, pack, water, and tools can change sag. Use your normal riding kit for a more realistic spring estimate.
8. Is this calculator a final setup answer?
No. It gives a strong starting point. Confirm with measured sag, trail feel, travel use, and real riding conditions before final tuning.