What are suspension shims?

Shock absorber shims are small, thin metal plates that play a major role in the operation of shock absorbers and front forks. They are used in so-called shim stacks and help regulate the oil flow within the damper. In doing so, they influence the damping, handling, and tuning of a motorcycle, bicycle, or other vehicle with high-performance suspension. You can view them as the determinants of the shock absorber's DNA.

Because suspension shims are often only a few tenths of a millimeter thick, they might appear to be a simple component. In reality, a good shim actually requires precise dimensions, reliable material, and consistent quality.

What is a shim?

A shim is a thin plate used to technically influence clearance, tension, fit, or movement. Shims are found in many different machines and applications. In suspension applications, shims are used in shock absorbers and front forks. ShockShim specifically focuses on suspension shims: thin metal shims that are part of a damping system. They are placed in a shim stack and flex in a controlled manner under oil pressure. As a result, they help determine how quickly oil can flow through the damper and, therefore, how the shock absorber responds.

Where are suspension shims used?

Suspension shims are primarily used in:

• Shock absorbers
• Front forks
• Motorsport suspension
• Motorcross and enduro suspension
• Mountain bike suspension
• Automotive performance suspension
• Industrial or specialist dampers

They are of interest to suspension specialists, tuners, workshops, and manufacturers who want to precisely adjust the damping of a system.

How does a suspension shim work?

In a shock absorber, oil is guided through small openings and valves. When the damper is compressed or extends, pressure builds up in the oil. This pressure causes the shims in the shim stack to open or flex in a controlled manner. The ease or difficulty with which the shims flex affects the damping. This means that the shim stack influences how the suspension responds to, for example, minor bumps, hard impacts, braking, accelerating, or landing after a jump.

A suspension shim therefore does not function as a standalone component, but as part of a larger system. The combination of diameter, thickness, material, and the order within the shim stack determines how the damper behaves.

What is a shim stack?

A shim stack is a stacking of multiple shims with different dimensions and thicknesses. By placing shims in a specific order, a suspension specialist can precisely adjust the damping.

A shim stack can, for example, influence:

• Compression damping
• Rebound damping
• Sensitivity to small movements
• Support during larger impacts
• Modification progression

Therefore, choosing the right shim is not just a matter of size, but also of function within the overall stack.

Why are the dimensions important?

For suspension shims, three dimensions are essential:

Inner diameter
The inner diameter determines how the shim fits onto the shaft, valve, or mounting.

Outer diameter
The outer diameter influences the surface area covered by the shim and how the oil can move along or through the system.

Thickness
The thickness has a significant influence on how stiff or flexible the shim is. A small change in thickness can have a noticeable effect on damping.

Therefore, shims are often designated by three sizes, for example: 8 x 30 x 0.15 mm

This usually means: inner diameter x outer diameter x thickness

Why is the material important?

Suspension shims are subjected to heavy loads. They must be able to bend repeatedly without losing their function and shape. Therefore, the material is important. A good shim must be dimensionally stable, resilient, and reliable.

At ShockShim, shims are made of hardened spring steel, Sandvik 7C27Mo2. This material is suitable for applications where resilience, wear resistance, and consistent performance are important.

Another material frequently encountered in the market is C20. The main difference lies in its composition and corrosion resistance. C20 is an ASTM 1095 type carbon steel with approximately 1% carbon and is primarily known for its high fatigue strength, wear resistance, and reliable performance under bending and impact loads. C27, on the other hand, is a martensitic stainless chromium steel with molybdenum. As a result, this material offers better corrosion resistance and higher corrosion fatigue strength than conventional carbon steels. In practice, this means that 20C is a fine choice for many standard shock absorber shims, while C27 is interesting when quality is even more important and the shim must be reliable for the long term.

For suspension specialists and manufacturers, that consistency is essential. When a shim theoretically has the same size but reacts differently in practice, it can affect the damper's tuning. 

Who is suspension shim important for?

Suspension shims are particularly relevant for professionals working with suspension and damping, such as:

• Suspension tuners
• Motorsport workshops
• Motorcross and enduro specialists
• Mountain bike suspension specialists
• Shock absorber manufacturers
• Technical suppliers
• OEMs and small and large series producers

Standard shims and custom shims

Many suspension shims are available in standard sizes. This is convenient for workshops and tuners who regularly require the same dimensions.

However, there are also situations where customization is necessary. For example, when:

• A specific inner diameter is required
• A non-standard outer diameter is desired
• A specific thickness is not available as standard
• A manufacturer has its own damper design
• An existing shim stack needs to be optimized

In such cases, a custom shim can be the right solution. Shockshim has a large number of dies with which we produce standard sizes. For non-standard sizes, we have a self-produced laser cutting machine. This allows us to supply shims that are not available as standard orders.

Order suspension shims from ShockShim

ShockShim supplies precision shims for use in shock absorbers, front forks, and suspension shim stacks. The shims are available in many different inner diameters, outer diameters, and thicknesses.

Thanks to the combination of precise sizing, reliable material, and manufacturing experience, the shims are suitable for suspension specialists, tuners, workshops, and manufacturers who require reproducible quality.

View the available sizes in the webshop or contact us for custom work.