SRAM PSI Calculator
Your expert tool for setting the perfect air pressure in your SRAM & RockShox suspension.
Your Recommended Starting Points
105 PSI
175 PSI
15-30%
5-8 clicks
These values are calculated based on general starting recommendations where rear shock pressure approximates rider weight in pounds, and fork pressure is slightly lower.
What is a SRAM PSI Calculator?
A sram psi calculator is an essential tool designed for mountain bikers to determine the optimal starting air pressure (measured in Pounds per Square Inch) for their front suspension forks and rear shocks, particularly those made by SRAM’s subsidiary, RockShox. Proper suspension setup is critical for bike performance, affecting traction, comfort, and control. This calculator simplifies the complex process by providing a scientifically-backed baseline based on the single most important factor: rider weight. Instead of guessing, you get a precise number to begin your tuning process, ensuring your bike performs as intended from the first pedal stroke.
SRAM PSI Calculator Formula and Explanation
The core of this calculator uses widely accepted baseline formulas to estimate suspension pressure. While exact factory settings can vary by specific model and frame leverage ratios, these formulas provide an excellent and reliable starting point for most riders.
- Rear Shock Pressure: A 1:1 ratio with rider weight in pounds is the industry-standard starting point.
- Front Fork Pressure: Generally requires less pressure than the rear shock, often around 60-70% of the rider’s weight in pounds.
- Rebound Damping: Heavier riders require more pressure and thus slower rebound (fewer clicks from closed) to control the higher spring force.
For more detailed tuning, consider a suspension sag calculator after setting your initial pressure.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Rider Weight | Total weight of the rider plus all gear. | lbs or kg | 100 – 250 lbs |
| Air Pressure | The amount of compressed air in the spring. | PSI (Pounds per Square Inch) | 50 – 250 PSI |
| Sag | The percentage of travel the suspension compresses under rider weight. | % | 15% (Fork) – 30% (Shock) |
| Rebound Clicks | Adjusts how fast the suspension returns to its full travel after a compression. | Clicks from fully closed | 0 – 20 |
Practical Examples
Example 1: Trail Rider
- Inputs: Rider Weight: 180 lbs.
- Units: Pounds (lbs).
- Results:
- Fork Pressure: ~108 PSI
- Shock Pressure: ~180 PSI
- Rebound: ~4-7 clicks from closed
Example 2: Lighter XC Rider
- Inputs: Rider Weight: 65 kg (approx. 143 lbs).
- Units: Kilograms (kg).
- Results:
- Fork Pressure: ~86 PSI
- Shock Pressure: ~143 PSI
- Rebound: ~7-10 clicks from closed
Understanding your settings is key. Many riders also use a bike fit calculator to ensure their body position is optimal, which also affects suspension dynamics.
How to Use This SRAM PSI Calculator
- Enter Your Weight: Input your complete riding weight, including shoes, helmet, and any pack you carry.
- Select Units: Choose between pounds (lbs) or kilograms (kg). The calculator handles the conversion automatically.
- Review Results: The calculator instantly provides your starting air pressure for both the fork and rear shock, along with a recommended rebound range.
- Apply and Test: Use a shock pump to set your suspension to the recommended PSI. Then, go for a ride and fine-tune based on feel.
Remember, this is a starting point. Aggressive riders or those on unique terrain may need to adjust further. Also, consider checking your mountain bike tire pressure calculator settings, as tires are the first line of suspension.
Key Factors That Affect Suspension PSI
While rider weight is primary, several other factors influence the ideal pressure for your SRAM suspension:
- Riding Style: Aggressive riders hitting large jumps may need 5-15% more PSI than casual trail riders.
- Frame Leverage Ratio: Different bike frames compress the rear shock at different ratios. Our calculator uses an average, but your frame manufacturer may have specific advice.
- Air Spring Volume (Tokens): Adding or removing “Bottomless Tokens” or volume spacers changes the spring curve. More tokens make the suspension more progressive (harder to bottom out) and may require slightly lower initial PSI. This is a topic worth exploring if you are interested in bottomless tokens explained.
- Temperature: Air pressure changes with ambient temperature. A 10°F change can alter PSI by ~2%. Set your pressure at the temperature you’ll be riding in.
- Sag Preference: While we recommend 15-20% for forks and 25-30% for shocks, some riders prefer a plusher (more sag) or firmer (less sag) feel.
- Rebound Damping: Your rebound setting works in tandem with air pressure. Correctly setting it is crucial. Our rebound settings guide can help.
- Rider Position: Your position on the bike, which can be optimized with a bicycle gear calculator, influences how weight is distributed between the front and rear wheels.
Frequently Asked Questions (FAQ)
1. Why is a sram psi calculator better than just guessing?
It provides a data-driven starting point based on physics and manufacturer guidelines, eliminating the wild inaccuracies of guesswork and getting you to an optimal setup faster.
2. How often should I check my suspension pressure?
It’s good practice to check before every ride. Air can slowly leak over time, and temperature changes can affect PSI.
3. What is “Sag” and why is it important?
Sag is how much your suspension compresses under your static weight. Setting sag correctly (usually 15-30%) ensures your wheel can track the ground effectively, extending into dips and compressing over bumps.
4. What if my weight is between the values on a printed chart?
This is where a digital sram psi calculator shines. It calculates the exact value for your specific weight, rather than forcing you to estimate between two points.
5. Can I use the same PSI for my fork and rear shock?
No. Rear shocks almost always require significantly higher pressure than forks due to the frame’s leverage ratio and weight distribution. A common starting point is PSI equal to your body weight in LBS for the rear shock.
6. What does “clicks from closed” mean for rebound?
This refers to turning the rebound knob all the way clockwise until it stops (the slowest setting, “closed”), and then counting the clicks as you turn it counter-clockwise.
7. Does temperature really affect my PSI?
Yes. According to Gay-Lussac’s Law, the pressure of a gas is directly proportional to its absolute temperature. A cold morning vs. a hot afternoon can change your PSI and ride feel.
8. What tool do I need to adjust suspension pressure?
You MUST use a dedicated high-pressure shock pump. A regular tire pump cannot reach the required pressures and will lose significant air when detached.