Shock Length & Stroke Calculator
Calculate required shock dimensions based on suspension geometry and travel goals.
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What Is a Shock Length Calculator?
A shock length calculator is a tool that figures out the correct shock stroke, compressed length, and extended length for your suspension.
Instead of picking a shock based on brand or guesswork, you calculate what your suspension actually needs.
The calculator uses:
- Ride height
- Up-travel (bump)
- Down-travel (droop)
- Motion ratio
- Safety buffer
From this, it outputs the shock dimensions that will physically fit your suspension without bottoming out or topping out.
Why Shock Length Matters More Than People Think
Shocks do more than smooth the ride. They also limit suspension movement.
If the shock is too long:
- It can bottom out before the suspension hits its bump stop
- Internal shock damage happens fast
- Mounts, shafts, and seals fail
If the shock is too short:
- You lose droop
- Tires lift early
- Traction and control suffer
Correct shock length protects your suspension and lets it use its full travel safely.
What This Shock Length Calculator Does
This calculator is built around suspension geometry, not marketing numbers.
It calculates:
- Required shock stroke
How much total shaft travel the shock must have. - Minimum compressed length
How short the shock must safely get at full bump. - Maximum extended length
How long the shock must reach at full droop. - Actual shaft travel
How much of the shock moves during bump and droop. - Wheel travel vs shock travel
Adjusted using motion ratio. - Bump vs droop bias
Shows how your travel is split. - Fitment validation
Lets you check a catalog shock before buying.
Inputs Explained in Simple Terms
Static Ride Height
This is the distance between shock mounts when the vehicle is sitting at rest.
Measure it with the vehicle fully assembled and on level ground.
Up-Travel (Bump)
How far the wheel moves upward from ride height.
This is what saves you when you hit a bump or land from a drop.
Down-Travel (Droop)
How far the wheel moves downward from ride height.
This keeps tires on the ground over uneven terrain.
Motion Ratio
This tells the calculator how much the shock moves compared to the wheel.
- Solid axle setups are usually close to 1.0
- IFS or IRS setups are often 0.5 to 0.8
Lower motion ratio means the shock moves less, but works harder.
Safety Buffer
Extra clearance to prevent internal bottoming.
This small number can save expensive parts.
How the Calculator Actually Works
Here is the logic in simple steps:
- Converts wheel travel into shock travel using motion ratio
- Adds safety buffer to both bump and droop
- Calculates physical mounting limits
- Determines ideal compressed and extended shock lengths
- Calculates total required shock stroke
- Displays bias and warnings based on your setup
The result is not a “nice” number. It is a correct one.
Understanding the Results
Required Shock Stroke
This is the minimum stroke the shock must have.
Always choose equal or greater stroke. Never less.
Min Compressed Length
The shock you buy must collapse shorter than this number.
If it cannot, it will bottom out internally.
Max Extended Length
The shock must extend at least this far.
Limit straps usually control final droop, but the shock still needs to reach this length.
Bump / Droop Bias
A balanced setup is often near 50/50.
- Too little bump travel increases bottoming risk
- Too little droop reduces traction
The calculator warns you when bias is extreme.
Built-In Fitment Validator
The calculator includes a fitment checker for real shocks.
You enter:
- Catalog compressed length
- Catalog extended length
The tool then tells you:
- If the shock fits safely
- How much clearance you have at full bump
- If the shock is unsafe
This feature alone can prevent expensive mistakes.
Common Mistakes This Calculator Helps Avoid
- Buying shocks based only on advertised stroke
- Ignoring motion ratio
- Forgetting safety buffer
- Assuming all “same travel” shocks fit the same
- Using the shock as a bump stop
These are common, costly errors.
Who Should Use a Shock Length Calculator?
This tool is useful if you are:
- Building or modifying a suspension
- Swapping axles
- Changing ride height
- Upgrading to longer travel shocks
- Designing an off-road or race setup
- Trying to fix repeated shock failures
If shocks are expensive or hard to replace, this calculator pays for itself fast.
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