Fox Suspension Calculator
Your ultimate tool for dialing in the perfect mountain bike suspension settings.
Enter your total weight in pounds (lbs), including all your riding gear (helmet, shoes, pack).
Select whether you are calculating for your front fork or rear shock.
Enter the total travel of your fork or shock in millimeters.
Recommended: 15-20% for Fork, 25-30% for Shock.
Recommended Air Pressure
Sag in Millimeters
Rebound (from closed)
Compression (from open)
Formula Used: This fox suspension calculator uses manufacturer-provided baseline data. Air pressure is estimated based on rider weight and suspension type. Rebound and compression are suggested starting points correlated with the calculated air pressure. Sag (mm) = Travel (mm) * (Sag % / 100).
What is a Fox Suspension Calculator?
A fox suspension calculator is a specialized tool designed to help mountain bikers determine the optimal starting settings for their Fox-branded forks and rear shocks. Instead of guessing, a rider can input specific variables like their weight and the suspension’s travel to get data-driven recommendations for air pressure, sag, and damping adjustments. This ensures the bike performs predictably and provides a solid baseline for further fine-tuning based on terrain and personal preference. This tool is an essential first step in any proper bike setup.
Who Should Use It?
Any mountain biker using Fox air suspension, from weekend warriors to seasoned racers, will benefit from using a fox suspension calculator. Proper setup is critical for safety, performance, and comfort. An incorrectly configured suspension can feel harsh, lack traction, or bottom out too easily, leading to a poor riding experience and even potential danger on the trail. This calculator demystifies the setup process, making it accessible to everyone.
Common Misconceptions
A common misconception is that the numbers from a fox suspension calculator are the final, perfect settings. In reality, they are expert-recommended starting points. Factors like riding style (aggressive vs. playful), typical trail conditions (rocky vs. smooth), and even temperature can influence the ideal setup. Riders should use these calculated values as a baseline and then bracket their settings—making small adjustments and testing them—to find what feels best for them. For more details, see our advanced tuning guide.
Fox Suspension Calculator Formula and Mathematical Explanation
The core of a fox suspension calculator isn’t a single complex formula, but a series of lookups and correlations based on extensive testing data from Fox. The primary calculation is for sag, which directly impacts the bike’s geometry and feel.
1. Sag Calculation: This is a simple percentage calculation.
Sag (in mm) = Total Suspension Travel (mm) * (Desired Sag Percentage / 100)
2. Air Pressure Estimation: This is the most complex part. The calculator uses a non-linear relationship between rider weight and the required air pressure to achieve the desired sag. This data is derived from charts provided by Fox for each specific fork and shock model. For example, a 180lb rider might need 88 PSI on a fork but 210 PSI on a shock for the same sag percentage due to different leverage ratios and air spring designs.
3. Damping Recommendations: Rebound and compression settings are directly correlated with spring rate (air pressure). Higher air pressure requires more rebound damping (slower) to control the faster return force of the spring. The calculator suggests a starting number of clicks from the fully closed (slowest rebound) or fully open (least compression) position.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Rider Weight | Total weight of the rider plus gear. | lbs or kg | 100 – 250 lbs |
| Suspension Travel | The maximum distance the suspension can compress. | mm | 100 – 200 mm |
| Sag | The percentage of travel the suspension compresses under rider weight. | % | 15% – 30% |
| Air Pressure | The primary variable for setting spring rate and sag. | PSI | 50 – 300 PSI |
| Rebound Damping | Controls how quickly the suspension returns after a compression. | Clicks from Closed | 1 – 16 clicks |
Practical Examples (Real-World Use Cases)
Example 1: Trail Rider Fork Setup
A trail rider weighing 175 lbs with gear has a Fox 36 fork with 160mm of travel. They want a balanced setup and aim for 20% sag.
- Inputs: Rider Weight = 175 lbs, Travel = 160 mm, Desired Sag = 20%
- Calculator Output:
- Air Pressure: ~90 PSI
- Sag: 32 mm
- Rebound: ~7 clicks from closed
- Interpretation: The rider sets their fork to 90 PSI and confirms that it sags 32mm when they are in the attack position on the bike. This balanced setup provides good support for climbing and descending. This is a classic use of the fox suspension calculator.
Example 2: Enduro Racer Shock Setup
An enduro racer weighing 200 lbs with gear is setting up their Fox Float X2 rear shock, which has a 65mm stroke. They prefer a more supple, traction-focused feel and aim for 30% sag.
- Inputs: Rider Weight = 200 lbs, Travel = 65 mm, Desired Sag = 30%
- Calculator Output:
- Air Pressure: ~230 PSI
- Sag: 19.5 mm
- Rebound: ~5 clicks from closed
- Interpretation: The racer sets their shock to 230 PSI. The 30% sag provides excellent small bump sensitivity and keeps the rear wheel tracking the ground on rough terrain, which is crucial for maintaining speed and control during a race. For more on racing setups, read our guide on enduro bike preparation.
How to Use This Fox Suspension Calculator
- Enter Your Weight: Start by entering your fully-kitted rider weight in pounds. Be honest! This is the most critical input for the fox suspension calculator.
- Select Unit and Travel: Choose between ‘Fork’ and ‘Shock’ and input the component’s travel in millimeters. You can find this spec on the manufacturer’s website or measure it.
- Set Desired Sag: Input your target sag percentage. As a rule of thumb, use 15-20% for forks (a firmer, more supportive feel) and 25-30% for shocks (a plusher, more traction-oriented feel).
- Review Your Results: The calculator will instantly provide a recommended air pressure, your sag in millimeters, and starting points for your rebound and compression dampers.
- Apply and Test: Use a shock pump to set your air pressure. Then, perform a sag test to verify. Adjust pressure in small increments until you hit the target sag in millimeters. Set your rebound and go for a ride on a familiar trail to test the settings.
Key Factors That Affect Fox Suspension Results
While a fox suspension calculator provides a fantastic baseline, several factors can require you to deviate from the suggestions. Understanding them is key to mastering your setup.
- Leverage Ratio: Every bike frame has a unique suspension linkage design with a specific leverage ratio. This ratio dictates how much the rear wheel moves for every millimeter the shock compresses. Bikes with a higher leverage ratio generally require higher air pressure in the shock. Our calculator approximates this, but your frame manufacturer may have more specific advice.
- Riding Style: An aggressive rider who hits large jumps and drops will likely need more air pressure and slower rebound than a less aggressive rider of the same weight to prevent bottoming out.
- Terrain: If you typically ride smooth, flowy trails, you might prefer less sag and faster rebound. For steep, chunky, technical terrain, more sag and slightly slower rebound can increase control and traction.
- Air Volume Spacers: These small plastic tokens can be added or removed from the air chamber of your fork or shock. Adding spacers makes the suspension more progressive (harder to bottom out), while removing them makes it more linear. If you find you’re using all your travel too easily, even with the correct pressure, consider adding a volume spacer. This is a key tuning step beyond the initial fox suspension calculator setup.
- Temperature: Air pressure changes with temperature. A setup dialed in on a cool morning may feel different on a hot afternoon. Be prepared to make small adjustments, especially if you experience significant temperature swings.
- Component Age and Service: Suspension performance degrades over time as seals wear and oil becomes contaminated. A freshly serviced fork or shock will feel more responsive and may require different settings than one that is due for maintenance. We recommend following Fox’s service intervals, which can be found in our maintenance schedule section.
Frequently Asked Questions (FAQ)
This can happen due to stiction in the seals (especially on new suspension) or variations in bike linkage. Always trust the physical measurement. Use the calculator’s pressure as a starting point, but add or remove air until you physically measure the correct sag in millimeters.
Rebound controls the speed at which your suspension extends after being compressed. Too fast, and the bike will feel like a pogo stick, losing traction. Too slow, and the suspension won’t recover in time for the next bump (known as “packing down”). The settings from the fox suspension calculator are a safe starting point.
You should always set your sag in the “attack position”: standing on the pedals, with your weight centered, as you would be when descending. This provides the most accurate representation of how the suspension will behave on the trail.
It’s good practice to check your air pressure before every ride. Air can slowly leak over time, and temperature changes also affect pressure. A quick check ensures your bike will perform consistently every time you head out.
Low-speed compression (LSC) controls how the suspension reacts to slow movements, like pedaling (bob) and body weight shifts. High-speed compression (HSC) manages impacts from fast events like hitting rocks, roots, and landing jumps. Not all forks/shocks have both adjustments. Start with both fully open, then add damping to control unwanted motion. Our compression damping guide has more.
No. This calculator is specifically tuned using data for Fox suspension products. Other brands like RockShox or Marzocchi have different air spring designs and will require different pressures. Use the manufacturer-specific calculator for those components.
If you’re between sizes or weights, it’s always better to start with the higher pressure recommendation. It’s generally safer to have slightly too much support than too little, which can lead to harsh bottom-outs.
No, this fox suspension calculator is for air shocks only. Coil shocks use a physical spring, and changing the “spring rate” requires swapping the coil itself. We have a separate coil spring calculator for that purpose.