Shim Stack Technology

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The use of thin steel shims is critical to the feel of any high-end suspension system and especially with the new DVO products. Our forks and shocks will be finely tuned with a generous combination of shim stacks to provide that stable and predictable suspension feel for both compression and rebound. Shims are used to restrict oil flowing through the holes or ports in a piston. Shims are configured in various diameters and thickness to achieve specific results as a “shim stack”.

The larger diameter shim that sits on the piston surface is the first shim to resist oil flow and generally affects the low-speed compression. The shims that are in the middle and furthest away from the piston’s surface affects the mid-high speed compression feel. When proper shim stack settings are achieved the end result is a bottomless feel on compression and a controlled/predicable extension that works in concert to keep your wheels planted on the ground. The main reason shim stacks are so amazing is that they are dynamic or speed sensitive and a proper stack can deliver a wide range of damping performance purely based on velocity.

Many companies use orifice or small holes to control compression and or rebound in their dampers, especially on lower end products. There are serious limitations to orifice dampers, under low speeds oil can easily flow through a hole but when speeds increase, oil flow becomes restricted and hydraulic locking occurs. Thats where a harsh feel on compression occurs or an unpredictable hopping of the front wheel on the rebound stroke can occur reducing traction and control.

A lot of mathematic calculations & years of tuning experience goes into our shim stack configuration. Below illustrates the use of a tapered stack that’s applicable for small bump absorbtion with a larger hit capability. Under Compression, oil is pushed through a port and lead into the shim stack. As the forces increase, the oil pushes open the shims. The shims create resistance to oil flow, which is your damping.

Shim Stack Overview

The shims that are first to be contacted by the oil create Low Speed Damping. The Crossover shim (#3) is to initiate a smooth transition from low speed to mid-speed damping. Shims 4-5 support mid level compression. As forces increase, the shims deeper into the stack start to resist which creates High Speed Damping. The thickness & diameter of the shims are critical for calculating damping settings from low-mid-high speed compressions. So why do tuners use a large number of thiner shims instead of a smaller number of thicker shims? The reason for using thinner shims is to prevent permanent distortion. If you were to take two shims, a thicker and a thinner one made of the same material and start bending them, the thicker shim will permanantley distort before a thinner shim does. Tuner’s then have to calculate how many thinner shims it takes to equal one thick shim. The result is a shim stack that will keep damping smooth and keep permanent distortion to a minimum.