ohlins spring calculator

What this Öhlins spring calculator does

Picking the right shock spring is one of the biggest setup wins you can make. If the spring is too soft, the bike rides low, uses travel too quickly, and feels vague on exits. Too stiff, and grip suffers because the rear skips and struggles to follow bumps.

This tool estimates the rear shock spring rate from your total load, target rider sag, and linkage ratio. It reports values in the three most common units:

• N/mm (common in many suspension catalogs)
• kg/mm (widely used in motorcycle setup conversations)
• lb/in (common in some racing and US references)

How the math works

Step 1: Estimate rear axle load

We split bike mass and rider/payload mass by rear bias percentages, then convert to force:

• Rear mass (kg) = bike mass × bike rear bias + payload × payload rear bias
• Rear force (N) = rear mass × 9.80665

Step 2: Compute required wheel rate

Wheel rate is how much force is needed per mm of rear wheel movement:

• Wheel rate (N/mm) = rear force / target sag

Step 3: Convert to shock spring rate

Because linkages create leverage, spring rate at the shock is higher than wheel rate:

• Shock rate = wheel rate × (motion ratio)² × style factor

The style factor slightly nudges the recommendation softer or stiffer depending on your intended feel.

Input tips for better accuracy

• Use real riding weight: include helmet, boots, backpack, hydration, and normal gear.
• Be honest about luggage: top boxes and tail packs significantly change spring needs.
• Measure motion ratio if possible: manufacturer data is best; rough guesses can miss by a lot.
• Set realistic sag targets: smaller sag generally pushes spring rate higher.

Quick reference table

Use Case	Typical Rear Rider Sag	General Spring Direction
Commuting / rough pavement	35–40 mm	Slightly softer for comfort and traction
Sport street	30–36 mm	Balanced response and grip
Track day	25–33 mm	Often stiffer for support under drive

Common mistakes when choosing a spring

1) Using preload to fix the wrong spring

Preload changes ride height and initial position, but it does not change true spring rate. If you need extreme preload just to hit sag, you likely need a different spring.

2) Ignoring payload changes

If you switch between solo riding and two-up touring, one spring may be a compromise. Some riders keep two spring options for different missions.

3) Chasing numbers without riding feedback

Use the calculator as a starting point, then validate with on-road or on-track behavior: grip on corner exits, stability under acceleration, and bump compliance.

Final setup checklist

• Install spring and set baseline preload.
• Measure free sag and rider sag carefully.
• Adjust preload to target sag range.
• Fine tune rebound/compression damping after spring is correct.
• Re-check with normal fuel load and tire pressures.

Done right, spring selection makes every other suspension adjustment easier. Start with good math, then finish with good testing.