6 Best Volume Spacer Kits For Custom Air Spring Curves

A bike’s suspension is the bridge between a rider’s ambition and the reality of the terrain. When a fork feels harsh or bottoms out on routine hits, the culprit is often the air spring curve, not the rider’s skill level. Mastering this small adjustment transforms a twitchy, unpredictable ride into a composed machine that tracks through technical rock gardens with confidence.

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RockShox Bottomless Tokens: The Industry Standard

RockShox Bottomless Tokens are the benchmark for a reason: they are simple, inexpensive, and universally understood. By threading these plastic spacers onto the air top cap, the total volume of the air chamber is reduced, creating a more progressive spring rate. This prevents the fork from blowing through its travel on heavy drops or high-speed square-edged hits.

These tokens are perfect for riders who want a “set it and forget it” solution for their RockShox forks. Because they are widely available and extremely durable, they offer the highest reliability for multi-day bikepacking trips where field repairs must be simple. If the current setup is consistently hitting the bump stops, adding a token is the most efficient path to increased bottom-out resistance.

However, the main trade-off is the lack of convenience, as changing the volume requires letting the air out and unscrewing the top cap. This is an ideal choice for the rider who values structural simplicity over on-trail adjustability. If the goal is a predictable, linear-to-progressive ramp-up for all-day trail riding, look no further than this standard.

Fox Air Volume Spacers: For Precision Tuning

Fox volume spacers—often referred to as “orange pucks”—provide a refined approach to tuning the FLOAT air spring. Unlike some competitors that use a singular threaded rod, these spacers snap into one another, allowing for granular adjustments to the spring curve. This modular system helps in achieving a very specific feel, whether the terrain demands a subtle ramp or a drastic increase in progression.

These spacers are engineered specifically for Fox suspension, ensuring a perfect seal and precise fit. They are recommended for riders who are sensitive to micro-adjustments in their suspension performance and ride a variety of terrains. For those who frequently switch between flowy, high-speed jump lines and slow-speed, chunky technical descents, this system provides the necessary control to keep the front end planted.

The investment in Fox-specific hardware pays off in long-term performance and ease of installation. If a fork feels too “mushy” in the mid-stroke but lacks support at the end of the travel, layering these spacers provides the necessary mid-to-end stroke ramp. They are a definitive choice for anyone running a Fox fork who refuses to compromise on suspension nuance.

Vorsprung Secus: The Ultimate Coil-Like Feel

The Vorsprung Secus is not a traditional spacer, but an external air spring upgrade that fundamentally changes how a fork handles initial impact. By increasing the negative air spring volume and adding a blow-off valve, the Secus creates a “plush” feel that mimics the sensitivity of a coil spring. It offers mid-stroke support while maintaining a buttery smooth response to small chatter.

This product is aimed at aggressive riders and racers who demand peak performance in the most demanding environments. It is a significant investment, but the performance gains for long, high-speed descents are undeniable. For those tackling big mountain alpine routes where arm pump and fatigue are limiting factors, the Secus provides the support needed to stay fresh during long days in the saddle.

Choosing the Secus implies a willingness to deviate from factory standards in favor of a more boutique, high-performance experience. While it is more complex to install than a simple plastic puck, the trade-off is a level of traction and composure that standard tokens cannot match. If the priority is absolute suspension refinement, the Secus is the gold standard.

MRP Ramp Control: Tune Progression On the Fly

The MRP Ramp Control cartridge replaces the standard air spring top cap with a mechanical dial that adjusts progression instantly. Rather than using fixed spacers, this system uses a velocity-sensitive valve to change how the air spring reacts to fast compressions. This is the ultimate tool for riders who encounter wildly varying terrain within a single ride.

This is a game-changer for someone who starts a day on smooth, rolling singletrack and ends on a steep, rugged enduro descent. By simply twisting a dial, the fork can be tuned for high-speed responsiveness or deep-travel support without carrying tools or letting air out. It removes the guesswork and the mess of performing mid-ride maintenance.

While the upfront cost is higher than a pack of plastic tokens, the convenience and performance benefits are unmatched for serious trail riders. It is the most technically advanced solution for on-trail tuning. If the desire is to stop compromising on setup and start controlling it, the MRP Ramp Control cartridge is the definitive upgrade.

Manitou IVA: Easy, On-Trail Adjustability

The Manitou Incremental Volume Adjuster (IVA) is an integrated feature on many Manitou forks that allows riders to adjust the volume of the positive air chamber without tools. By adjusting the position of a plunger within the air spring, the rider can effectively change the volume on the fly. This eliminates the need for spare parts or disassembly.

This system is perfect for the minimalist who wants to experiment with suspension settings during a long day of riding. It is exceptionally user-friendly, making it a great choice for riders who are just beginning to explore the benefits of suspension tuning. Because it is built directly into the fork, there is no risk of losing small plastic parts during a trailside adjustment.

For those who prioritize reliability and ease of use, the IVA is a standout. It offers enough range for most trail riding needs, providing a balanced, predictable feel that is easy to return to a baseline setting. It is the best choice for a rider who wants a high-tech solution that remains simple and accessible.

Cane Creek Spacers: For Helm and Kitsuma Forks

Cane Creek’s volume spacers are specifically designed to complement the unique architecture of the Helm and Kitsuma fork platforms. These forks are known for their high degree of adjustability, and the spacers play a vital role in fine-tuning the spring rate to match the damping characteristics. They are robust, easy to install, and designed for riders who value a highly customizable chassis.

These spacers are the right choice for owners of Cane Creek forks who want to maximize the potential of their suspension system. They allow for a precise “tune” that works in harmony with the externally adjustable high-speed and low-speed compression circuits. For a rider building a custom setup for specific, demanding terrain, these are essential.

The strength of the Cane Creek system lies in its ability to support a wider range of rider weights and riding styles. By dialing in the volume, the fork can remain supportive for heavier riders or those who hit large features without becoming overly stiff. If one already rides a Cane Creek fork, these spacers are the only logical path to a perfect, balanced ride.

Why and When to Tune Your Air Spring Curve

The air spring curve dictates how much force is required to compress the fork through its travel. A linear curve feels soft and uses travel easily, while a progressive curve gets stiffer as the fork compresses, preventing bottoming out. Tuning this curve is essential when a rider finds they are using all their travel on small bumps or, conversely, can never reach full travel even on the largest drops.

Terrain dictates the ideal setting for every rider. On fast, flowy trails with large jumps, a more progressive setup is often preferred to provide a platform for jumping. In contrast, on steep, rocky trails, a more linear setup might be better to maintain traction and utilize all available travel to absorb repetitive hits.

Recognize that volume spacers do not replace the need for proper air pressure (sag). Always set sag to the manufacturer’s recommendation before adjusting volume. Spacers should be used to refine how the fork handles the final 20% of its travel, not to compensate for an incorrect base air pressure.

Spacers vs. Damping: What’s the Difference?

A common misconception is that volume spacers provide the same control as compression damping. While spacers change the spring—the resistance to compression—damping controls the speed of that compression. Think of the air spring as the “bouncer” that keeps the fork from collapsing, while the damping is the “manager” that keeps the movement controlled and predictable.

If the fork feels “bouncy” or uncontrolled, adjusting the rebound or compression damping is the first step. If the fork feels fine but hits the bottom of its travel with a harsh “clack,” that is when volume spacers are needed. Using spacers to fix a lack of damping is a band-aid solution that often makes the fork feel harsh, rather than supported.

A balanced setup requires both systems to work in tandem. Proper volume spacers provide the support required for aggressive riding, while quality damping ensures that support is delivered without sacrificing traction. Always master the basics of damping before moving on to advanced air spring volume tuning.

How to Install and Test Your New Volume Spacers

Installing spacers is a standard mechanical task that requires only basic tools, such as a shock pump and a socket wrench. Always follow the manufacturer’s manual for the specific fork model to ensure the air spring is fully depressurized before attempting to remove the top cap. A small amount of suspension grease on the new spacer helps ensure a perfect seal during installation.

Once installed, it is crucial to test the new setup on a familiar trail. Start with the same air pressure used before the adjustment to clearly feel the difference in the ramp-up. Perform a series of tests, including small, repetitive bumps and at least one significant, controlled drop or feature.

If the fork feels too stiff, consider removing a spacer or slightly lowering the air pressure. Suspension tuning is an iterative process of testing, observing, and tweaking. Taking notes on how the fork responds to different setups will accelerate the learning process and build confidence in making future adjustments.

Reading Your O-Ring: Are You Using Full Travel?

The O-ring on the fork stanchion is the most honest indicator of how the suspension is actually performing. After a ride, the O-ring’s position shows exactly how much travel was utilized. If the ring is consistently pushed to the very top, the fork is bottoming out too frequently and likely requires more spacers.

If the O-ring is stuck mid-way through the stanchion despite hitting big features, the setup is likely too progressive. A perfectly tuned fork usually has the O-ring ending 5 to 10 millimeters from the bottom-out point on a typical ride. This leaves a small amount of “reserve” travel for the occasional unexpected “huck-to-flat” or high-speed emergency.

Use the O-ring as a diagnostic tool rather than a final score. A rider who rarely hits full travel may be missing out on traction and comfort, while one who always hits it might be exposing their bike to unnecessary strain. Tune until the O-ring tells a story of a controlled, capable, and efficient ride.

Tuning your air spring curve is a gateway to a more harmonious relationship with your bicycle. It shifts the experience from simply riding over obstacles to engaging with the terrain with precision and control. Take the time to experiment, trust the feedback from the trail, and focus on the joy of a fork that finally feels like an extension of your own intent.