Shim Stack Calculator
Estimate suspension valve shim stiffness, clamp ratio, port coverage, force, and relative deflection from real stack dimensions.
⚙Real Shim Stack Presets
Choose a starting point, then adjust the stack layers, clamp diameter, oil pressure, and safety factor for your valve assembly.
🔧Valve and Shim Inputs
Shim Stack Results
📊Material and Spec Comparison
📐Shim Material Reference
| Material | Modulus | Density | Use in stacks |
|---|---|---|---|
| Blue spring steel | 200 GPa | 7.85 g/cm³ | Baseline fork and shock shims |
| 17-7 stainless spring | 193 GPa | 7.75 g/cm³ | Corrosion resistant dampers |
| Chromoly spring steel | 205 GPa | 7.85 g/cm³ | Firm race compression stacks |
| Beryllium copper | 130 GPa | 8.25 g/cm³ | Special low-friction light stacks |
| Titanium shim stock | 116 GPa | 4.50 g/cm³ | Lightweight custom dampers |
| Carbon spring steel | 210 GPa | 7.80 g/cm³ | High response test stacks |
📏Thickness Effect Table
| Shim thickness | Relative single-shim stiffness | Common role | Practical note |
|---|---|---|---|
| 0.08 mm | 0.51× | Plush face shim | Very sensitive to handling damage |
| 0.10 mm | 1.00× | Baseline face shim | Most comparisons start here |
| 0.12 mm | 1.73× | Firm support shim | Small increase feels large |
| 0.15 mm | 3.38× | Backing or clamp shim | Often changes high-speed support |
| 0.20 mm | 8.00× | Clamp washer | Usually not a flexible face shim |
🛠Circuit Setup Reference
| Circuit | Typical face OD | Typical clamp | Target behavior |
|---|---|---|---|
| Fork base compression | 22-28 mm | 7-10 mm | Initial plushness with bottoming support |
| Fork mid-valve | 18-24 mm | 6-9 mm | Ride height and mid-stroke control |
| Shock main compression | 28-44 mm | 10-16 mm | Chassis hold-up and impact control |
| Shock rebound | 24-38 mm | 9-14 mm | Return speed and packing resistance |
| MTB damper | 12-22 mm | 4-8 mm | Small-volume response and support |
| Small-bore RC damper | 6-12 mm | 2-4 mm | Low-force flow control |
⚖Clamp and Coverage Guide
| Check | Formula | Preferred range | Meaning |
|---|---|---|---|
| Free span | (Face OD - clamp) / 2 | 5-16 mm | Longer span bends easier |
| Clamp ratio | Clamp / face OD | 0.28-0.48 | Higher ratio stiffens the face shim |
| Port cover | (Face OD - port OD) / 2 | 0.8-3.0 mm | Positive value keeps ports covered |
| Stack height | Sum of qty x thickness | Per piston spec | Must fit thread and cup geometry |
💡Calculation Tips
Suspension tuning are the process of changing components of the suspension, such as shims and oil weight, to change the way the motorcycle’s suspension behave. Many people attempt to tune the suspension by changing one shim at a time, but suspension tuning isnt a linear process. Changing the dimensions of one of the shims can have a largeer effect on the valve because of the physics of the shim.
One of the factors to consider when changing the shims is the thickness of the shim. The stiffness of the shim dont increase at the same rate as the thickness of the shim. If a rider changes a shim from 0.10mm to 0.12mm, there is more material in the shim, but the stiffness increase at a greater rate.
How Shims Affect Motorcycle Suspension
This is due to the fact that the stiffness of a shim is related to the cube of the thickness of the shim. To compare two different setups of the suspension’s shims, you can use an relative stiffness index. This value translates the dimensions of the shims into a number, and with this number, it is possible to compare the two shim setups without using guesswork.
Another of the factors to consider is the relationship between the shim and the piston and ports of the suspension. If the face shim is too small, it may not cover the port window when the valve lift. If the face shim does not cover the port window, there will be a leak in the system, which will make the suspension feel soft.
To avoid this issue, it is important to ensure that the port cover margin allow the face shim to cover the port window. Otherwise, the suspension will leak. Another of the factors to consider is the clamp diameter of the shim.
The clamp diameter is the size of the shim that contact the suspension case. The ratio of the clamp diameter to the outer diameter of the face shim determines how much the shim flex. A larger clamp ratio will make the shim feel stiffer.
Two dampers that have the same shims could have a different amount of damping force if the clamp diameters of the shims is of different size. The material of the shim impacts the modulus of elasticity of the shim. The modulus of elasticity impacts the way that the valve open.
Instead of using steel shims, which are the most common, you can use materials like titanium and beryllium copper. A lower modulus of elasticity allow for the valve to open at a lower pressure. Instead of focusing on the material of the shim, most people focus on the taper of the shim stack.
A pyramid stack is made up of shims of decreasing size, and this taper create a different high-speed damping than a linear shim stack. The high-speed damping of a suspension valve is referred to as the knee of the damping curve. You can tune the knee by adding crossover gaps or preload to the suspension.
Adding crossover gaps or preload will soften the transition of the knee of the damping curve. A softerer transition of the knee can make the suspension feel more forgiving for the rider. A calculator can be used to calculate the valve lift of a given set of shims.
Calculating the valve lift will show how much the shims move at a specific suspension pressure. Environmental factors can impact how the suspension performs. The temperature of the suspension change the viscosity of the oil within the suspension.
Additionally, heat changes how the metal components of the suspension react to one another. These factors indicate that the suspension should of include a safety factor in its design. This safety factor provide for variables like heat in the suspension.
Additionally, acknowledging the effect of environmental variables acknowledges the difference between a suspension setup in a lab versus the suspension setup in a race environment. Using a relative stiffness index and a calculator will allow people to move away from the trial-and-error processes often use to tune a motorcycle’s suspension. By comparing the relative stiffness of a new shim design to the current suspension setup, people can make changes that will accomplish the desired result.
Using engineering to understand the relationship between shim thickness, shim diameter, and pressure allow people to make intelligentely adjustments to the suspension components.
