Ohlins Shock Calculator
Calculate the ideal spring rate for your performance suspension setup.
Your weight in full riding gear.
The total travel of the rear shock absorber.
Ratio of wheel travel to shock travel. Check your bike’s specs.
Percentage of shock stroke used when you are on the bike.
Recommended Spring Rate
— mm
Target Rider Sag
— kg
Effective Sprung Mass
— N
Required Spring Force
Formula: Spring Rate (N/mm) = (Rider Force at Shock) / (Target Sag at Shock)
Spring Rate Comparison Chart
Visual comparison of calculated spring rate for different riding styles.
Typical Sag Recommendations
| Riding Discipline | Recommended Sag (%) | Characteristics |
|---|---|---|
| Road Racing / Track | 25-30% | Firmer feel, more responsive, better for smooth surfaces. |
| Aggressive Street / Canyon | 30-33% | Balanced performance for mixed-quality roads. Good compromise. |
| Enduro / Trail MTB | 30-35% | More compliance for rough terrain, improved traction. |
| General Street / Touring | 33-38% | Comfort-oriented, plush ride over bumps. |
| Downhill (DH) MTB | 35-40% | Maximum traction and bump absorption for steep, rough tracks. |
This table provides general sag guidelines. Use our ohlins shock calculator for a specific recommendation.
What is an Ohlins Shock Calculator?
An ohlins shock calculator is a specialized tool designed to determine the optimal spring rate for your motorcycle or mountain bike’s rear suspension. Unlike generic calculators, an ohlins shock calculator focuses on the high-performance characteristics and precision adjustments associated with Öhlins suspension systems. It takes key rider and vehicle data to recommend a spring that will provide the correct sag and support, forming the foundation of a perfectly balanced suspension setup. Proper spring rate is the single most important factor in suspension tuning, affecting everything from chassis stability and tire grip to rider comfort and confidence.
This tool is essential for serious racers, track day enthusiasts, and meticulous street riders who demand the most from their machine. If you have invested in a high-quality suspension like Öhlins, using a precise ohlins shock calculator ensures you unlock its full potential. A common misconception is that damping adjustments (compression and rebound) can fix an incorrect spring rate. In reality, damping controls the speed of suspension movement, while the spring is responsible for holding the ride height and resisting bottoming out. Without the correct spring, no amount of damping adjustment will make the bike handle correctly. For a deeper dive into setup, check out this suspension setup guide.
Ohlins Shock Calculator Formula and Mathematical Explanation
The core of any ohlins shock calculator is based on fundamental physics principles, specifically Hooke’s Law (Force = Spring Constant × Displacement). The goal is to find a spring constant (Rate) that correctly supports the rider’s weight at a desired sag point. The calculation must account for the leverage the suspension linkage exerts on the shock.
The step-by-step process is as follows:
- Calculate Target Sag (mm): This is the desired compression of the shock under the rider’s weight. It’s found by multiplying the total shock stroke by the desired sag percentage. `Target Sag (mm) = Shock Stroke (mm) * (Sag Percentage / 100)`
- Calculate Rider Force at the Wheel (N): This is the gravitational force from the rider’s mass. We must also account for the bike’s weight distribution. A simplifying assumption often made by an ohlins shock calculator is that a certain portion of the rider’s weight is supported by the rear shock. For this calculator, we primarily use the rider’s direct weight for simplicity, which is a common method for baseline calculations. `Rider Force (N) = Rider Weight (kg) * 9.81 m/s²`
- Calculate Force at the Shock (N): The suspension linkage creates a lever effect. The force seen by the shock is the force at the wheel divided by the motion ratio. `Force at Shock (N) = Rider Force (N) / Motion Ratio`
- Calculate Required Spring Rate (N/mm): Finally, the spring rate is the force required at the shock divided by the distance it needs to compress (the target sag). `Spring Rate (N/mm) = Force at Shock (N) / Target Sag (mm)`
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Rider Weight | Mass of the rider with all gear | kg | 60 – 120 |
| Shock Stroke | Total travel of the shock absorber | mm | 45 – 75 |
| Motion Ratio | Wheel Travel / Shock Travel | Unitless | 2.0 – 3.5 |
| Sag Percentage | Target sag under rider weight | % | 25 – 40 |
Practical Examples (Real-World Use Cases)
Example 1: Track Day Rider
- Inputs: Rider Weight = 90 kg, Shock Stroke = 65 mm, Motion Ratio = 2.5, Desired Sag = 28% (Track focus)
- Calculation:
- Target Sag = 65 mm * 0.28 = 18.2 mm
- Rider Force = 90 kg * 9.81 = 882.9 N
- Force at Shock = 882.9 N / 2.5 = 353.16 N
- Spring Rate = 353.16 N / 18.2 mm = 19.4 N/mm
- Interpretation: The ohlins shock calculator recommends a spring rate of approximately 19.4 N/mm (or the closest available, likely a 95 or 100 N/mm spring, as they are often sold in increments of 5 N/mm, which is approx 28 lb/in). This stiff setup minimizes sag, keeping the geometry sharp for quick turn-in on a smooth track.
Example 2: Trail Mountain Biker
- Inputs: Rider Weight = 75 kg, Shock Stroke = 50 mm, Motion Ratio = 3.0, Desired Sag = 33% (Trail focus)
- Calculation:
- Target Sag = 50 mm * 0.33 = 16.5 mm
- Rider Force = 75 kg * 9.81 = 735.75 N
- Force at Shock = 735.75 N / 3.0 = 245.25 N
- Spring Rate = 245.25 N / 16.5 mm = 14.86 N/mm
- Interpretation: The ohlins shock calculator suggests a rate of 14.86 N/mm. This softer spring allows the suspension to sit deeper into its travel, improving traction and bump absorption on uneven trails, which is crucial for maintaining control. Riders might explore different rear shock absorbers to find the perfect match.
How to Use This Ohlins Shock Calculator
Using our ohlins shock calculator is a straightforward process to get a highly accurate baseline for your suspension setup. Follow these steps:
- Enter Rider Weight: Put on all your typical riding gear (helmet, leathers/jacket, boots, etc.) and weigh yourself. Enter this value in kilograms (kg).
- Enter Shock Stroke: This information is available in your motorcycle’s service manual or on the manufacturer’s website. It is the physical travel of the shock itself, not the wheel. Enter it in millimeters (mm).
- Enter Motion Ratio: This is a critical but sometimes hard-to-find number. It’s the ratio of how much the rear wheel moves for every unit the shock moves. If you cannot find it, a typical range for sportbikes is 2.2-2.8 and for dirt/adventure bikes is 2.8-3.5. An incorrect value here will significantly affect the ohlins shock calculator result.
- Select Desired Sag: Choose a sag percentage based on your primary riding style from the dropdown menu. Race/Track settings are firmer (less sag), while Street/Comfort settings are plusher (more sag).
- Read the Results: The calculator instantly provides the recommended spring rate in N/mm. It also shows key intermediate values like the calculated target sag in mm, which you can verify with a physical measurement.
The “Copy Results” button allows you to save your calculated setup for future reference. Always use the calculated rate as a starting point and fine-tune your motorcycle sag and damping settings for personal preference.
Key Factors That Affect Ohlins Shock Calculator Results
Several factors can influence the ideal spring rate. Our ohlins shock calculator accounts for the main ones, but it’s important to understand the variables at play.
- Rider Weight: This is the most significant factor. A heavier rider compresses a spring more than a lighter rider, thus requiring a stiffer spring to achieve the same sag percentage.
- Motion Ratio: A bike with a high motion ratio (e.g., 3:1) has more leverage on the shock and requires a significantly stiffer spring than a bike with a low ratio (e.g., 2:1) for the same rider weight.
- Riding Style/Discipline: A track rider needs a stiff setup to maintain geometry under heavy braking and acceleration. A touring rider prioritizes comfort and needs a softer spring to absorb road imperfections.
- Shock Angle: While not a direct input in this simplified ohlins shock calculator, the angle of the shock relative to the swingarm affects the effective motion ratio throughout the travel. More progressive linkages may require different considerations.
- Cargo and Passenger Load: If you frequently ride with a passenger or heavy luggage, you should perform the calculation with the additional weight to find a suitable compromise or consider a spring for loaded conditions.
- Tire Profile and Pressure: The tires are the primary suspension component. Softer-carcass tires or lower pressures can absorb some initial harshness, which might allow a rider to use a slightly stiffer spring for better chassis support. A tire pressure calculator can help optimize this.
Frequently Asked Questions (FAQ)
What’s the difference between spring rate and preload?
Spring rate is the stiffness of the spring (force per unit of displacement, e.g., N/mm). It’s a fixed property of the spring itself. Preload is the amount of initial tension applied to the spring before any external load is added. Preload is used to adjust the ride height (sag), but it does not change the spring’s stiffness.
Why is sag so important?
Sag ensures your suspension is in the optimal part of its travel. It allows the wheel to drop into depressions (maintaining tire contact) and also provides travel to absorb bumps. Incorrect sag, as determined by an ohlins shock calculator, means the bike will either be too harsh and lack grip, or too soft and bottom out easily.
Can I use this ohlins shock calculator for my front forks?
This specific calculator is designed for rear shocks due to the motion ratio component. Front forks have a 1:1 motion ratio, but the calculation is slightly different as it involves two fork legs. However, the principles are the same, and you can find specific calculators for fork upgrade kits.
What if the calculated rate is between two available springs?
It’s generally recommended to choose the stiffer option. It is easier to manage a slightly stiff spring with damping adjustments than it is to compensate for a spring that is too soft and bottoms out frequently.
How often should I check my sag?
You should check your sag periodically, especially if your weight changes or if you start carrying luggage. It’s the best way to confirm your spring rate, as calculated by the ohlins shock calculator, is still correct for your use case.
Does this calculator work for both coil and air shocks?
This calculator is primarily for determining the rate of a coil spring. Air shocks act as an “air spring,” and their rate is adjusted by changing the air pressure. However, understanding the equivalent spring rate can still be useful for tuning.
What are “clicks” for compression and rebound?
These are the damping adjustments. They control the speed at which the shock compresses and extends. An ohlins shock calculator provides the spring rate, which is the starting point. Damping is tuned after the correct spring and sag are set. You can learn more in our suspension setup guide.
Where can I get help with installation?
If you’re not comfortable installing suspension components yourself, we highly recommend you contact us or a certified Öhlins service center. Incorrect installation is a major safety risk.