Fox DHX2 Spring Rate Calculator
Determine the optimal coil spring weight for your mountain bike setup.
Includes helmet, shoes, pack, and all riding gear.
The total vertical travel of your rear wheel.
The length of the shock shaft travel (e.g., 60, 65).
Recommended 25-30% for DH/Enduro applications.
Calculated Ideal Rate:
Recommended Fox Spring (Standard):
Firmer Option (Jump/Park):
Softer Option (Tech/Grip):
Estimated Preload Required:
Mastering Your Fox DHX2 Setup
The Fox DHX2 is a high-performance coil shock designed for downhill and enduro mountain biking. Unlike air shocks, which allow for infinite adjustability via a shock pump, coil shocks require the physical replacement of the steel or SLS (Super Light Steel) spring to achieve the correct sag.
How This Calculation Works
This calculator determines your ideal spring rate (measured in lbs/in) based on the leverage ratio of your frame and your total riding weight.
- Leverage Ratio: This is the ratio between how much your rear wheel moves (Wheel Travel) versus how much the shock compresses (Shock Stroke). A higher leverage ratio requires a stiffer spring.
- Rider Weight: This must include your "riding weight," not just your body weight. Helmet, pads, hydration pack, and shoes can easily add 10-15 lbs.
- Rear Bias: We utilize a standard 65% rear weight distribution bias, which is typical for modern geometry enduro and downhill bikes in the attack position.
Understanding Sag
Sag is the amount the suspension compresses under the rider's static weight. For the DHX2 on most frames, 30% sag is the "sweet spot" for traction and small bump sensitivity.
- 30% Sag (Standard): Provides the best balance of grip and support for general riding.
- 25% Sag (Firm): Better for smooth jump lines, bike parks, or riders who prefer a poppy feel.
- 35% Sag (Soft): Prioritizes maximum traction on steep, loose, and technical terrain but risks bottoming out on big hits.
Choosing Between Spring Sizes
Coil springs are typically sold in 25lb or 50lb increments (e.g., 400, 425, 450 lbs/in). It is rare for a calculation to land exactly on a manufactured size.
If your calculated rate is 435 lbs/in, you must choose between a 425 spring (more sag, plush feel) or a 450 spring (less sag, supportive feel). Use the preload collar to fine-tune the sag, but never exceed the manufacturer's maximum preload turns (usually 2 full turns) to avoid coil binding.