Leverage Ratio

Summary

Leverage ratio describes the relationship between rear-wheel movement and shock compression on a full-suspension bicycle. It is normally expressed as wheel travel divided by shock stroke. Because the ratio can change as the suspension moves, it influences the force, spring rate, and damping the shock must provide at different points in the travel. Leverage ratio is important when evaluating suspension progression and selecting shock settings, but it does not determine ride quality by itself. Shock design, spring curve, damping, friction, tires, frame geometry, and rider setup all contribute to what the rider feels.

Quick Facts

Category: Suspension concept
Measured as: Rear-wheel movement ÷ shock movement
Expressed as: A ratio, such as 2.5:1
Used on: Full-suspension bicycles
Influences: Wheel rate, spring requirements, damping, and progression
Determined by: Pivot locations, links, and shock mounting position

Overview

A leverage ratio of 2.5:1 means the rear wheel moves 2.5 millimeters for every millimeter of shock compression. The linkage therefore allows a relatively short shock stroke to control a larger amount of wheel travel.

Leverage ratio is a kinematic property of the frame. Air pressure, coil rate, compression damping, and volume spacers do not change the ratio itself. They change how the shock responds to the movement and forces produced by that ratio.

Most suspension systems do not maintain one ratio throughout their travel. Engineers alter pivot locations and link dimensions to create a leverage curve suited to the bike’s intended use.

How It Works

Average Leverage Ratio

Average leverage ratio is calculated using total rear-wheel travel and total shock stroke:

Average leverage ratio = rear-wheel travel ÷ shock stroke

For example:

Rear travel: 150 mm
Shock stroke: 60 mm
Average leverage ratio: 150 ÷ 60 = 2.5:1

This number is useful for estimating spring requirements and comparing basic frame specifications. It does not show how the ratio changes within the travel.

Instantaneous Leverage Ratio

Instantaneous leverage ratio is the relationship between very small amounts of wheel and shock movement at a particular suspension position. It is normally calculated using suspension-analysis software or measured from a linkage model.

A leverage curve plots these instantaneous values from full extension to bottom-out. This curve provides more useful information than the average because it shows how the shock’s mechanical advantage changes around sag, through the middle of the travel, and near bottom-out.

The RockShox Suspension Theory Guide uses wheel travel divided by shock stroke as its leverage-ratio convention. Some engineering and automotive sources use the inverse, so the graph labels should always be checked before comparing data.

Force and Wheel Rate

Leverage ratio affects force as well as movement. Ignoring friction, a 3:1 ratio means that a 100-newton force at the wheel produces approximately 300 newtons at the shock.

For a constant leverage ratio, the effective spring rate at the wheel is approximately:

Wheel spring rate = shock spring rate ÷ leverage ratio²

This squared relationship is important. A frame with a higher leverage ratio generally requires a stiffer coil spring or higher air-spring pressure to provide the same support at the wheel.

Higher leverage also reduces the effect of a fixed amount of shock-seal friction as felt at the wheel. However, it gives the shock less shaft movement for a given amount of wheel travel and requires the damper to produce greater internal force. Lower leverage produces more shock movement and shaft speed but requires less shock spring and damping force.

Neither approach is inherently better. The shock must be designed and tuned for the forces and speeds created by the frame.

Leverage Curve Types

Progressive

The leverage ratio decreases as the suspension compresses. For example, a curve might begin at 3.0:1 and finish at 2.4:1.

As the mechanical advantage decreases, progressively more wheel force is required to compress the shock. This can increase support and bottom-out resistance. It is also called a rising-rate design because the effective wheel rate rises, even though the numerical leverage ratio falls.

Linear

The leverage ratio remains approximately constant. The shock’s spring curve supplies most of the change in wheel rate. A perfectly constant curve is uncommon, but some frames are close to linear through much of their travel.

Regressive

The leverage ratio increases as the suspension compresses. This gives the wheel greater mechanical advantage over the shock deeper in the stroke. A regressive section can help the suspension move through part of its travel but may reduce bottom-out support unless balanced by a progressive air spring or other design features.

Mixed

Some curves change direction. A frame may be slightly regressive near full extension, relatively linear around sag, and progressive toward bottom-out. These shapes are used to tune specific parts of the stroke rather than produce one uniform characteristic.

Why It Matters

Leverage ratio helps determine:

The air pressure or coil rate required to achieve sag
The damping range needed to control the wheel
How rapidly effective wheel rate changes through the travel
How much shock friction is apparent at the wheel
Whether a particular shock is suitable for the frame
How much bottom-out resistance comes from the linkage

The leverage curve must be considered together with the shock’s spring curve. A progressive frame paired with a progressive air spring can produce considerably more end-stroke support than the same frame with a nearly linear coil spring.

Rider Experience

A decreasing leverage ratio can contribute to a supportive mid-stroke and greater bottom-out resistance. A higher initial ratio may help the suspension begin moving against shock-seal friction.

These tendencies are not guarantees. A highly progressive curve can still feel soft if the spring is under-supported, while a relatively linear frame can have substantial ramp-up when fitted with a progressive air shock.

Riders usually feel the combined wheel-rate curve rather than the leverage curve alone. Sag, air volume, coil rate, damping, tire pressure, and pivot condition can easily overshadow small differences in leverage ratio.

Mechanic’s Perspective

Leverage ratio becomes particularly useful when selecting coil springs or diagnosing a shock that operates near the end of its adjustment range.

Average ratio can provide a starting point for spring calculations, but rider weight distribution, sag target, leverage progression, and manufacturer recommendations must also be considered. FOX, for example, includes rear travel, shock stroke, sag, and suspension progression in its coil-spring rate calculator.

The ratio itself does not require maintenance and does not change as bearings wear. Worn pivots, dry bushings, shock-hardware play, or internal shock problems can nevertheless prevent the suspension from behaving as the curve predicts.

Changing shock stroke is not a safe method of altering leverage ratio or travel. A longer stroke can cause tire, linkage, shock, or frame contact. Eye-to-eye length, stroke, mounting hardware, reservoir clearance, spring compatibility, and damper tune should all be confirmed with the frame manufacturer. RockShox rear-shock fitment guide

Design Trade-Offs

Characteristic	Higher Leverage Ratio	Lower Leverage Ratio
Shock movement for a given wheel movement	Less	More
Force transmitted to the shock	Higher	Lower
Required shock spring rate	Higher	Lower
Required shock damping force	Higher	Lower
Effect of shock friction at the wheel	Reduced	More apparent
Shock shaft speed for a given wheel speed	Lower	Higher

These are mechanical tendencies, not complete descriptions of ride quality.

Buying Considerations

A lower average ratio is not automatically more controlled, and a higher ratio is not automatically more sensitive. Buyers should place more weight on the complete leverage curve, shock specification, available tuning range, geometry, and intended use.

A frame with uncommon shock dimensions or unusually high spring and damping requirements may also offer fewer replacement or upgrade options. Manufacturer setup charts and approved-shock lists are more useful than comparing average ratios alone.

Common Questions

Does a progressive leverage curve prevent bottom-out?

It helps, but spring pressure, coil rate, air volume, damping, bump-stop design, and impact energy also matter.

Do volume spacers change leverage ratio?

No. They change the air spring’s progression, not the frame’s mechanical leverage curve.

Can a flip chip change leverage ratio?

Some do. Others adjust only geometry, while certain designs change both geometry and progression. Check the manufacturer’s documentation.

Is a coil shock suitable for every progressive frame?

No. The frame must have sufficient progression, clearance, and manufacturer approval for the specific shock and spring.

Is average leverage ratio enough to compare bikes?

No. Two frames can have the same average ratio but very different instantaneous curves and ride characteristics.