Shock Length Calculator
Getting your suspension setup right is critical for performance, safety, and comfort. Whether youโre working on a mountain bike, motorcycle, car, or off-road vehicle, knowing the correct shock absorber length is essential for optimal suspension geometry and ride quality.
Our Shock Length Calculator helps you easily determine the correct eye-to-eye length and stroke length of your shock absorber based on your frame geometry and suspension travel. This tool saves you time, removes guesswork, and ensures your vehicle handles perfectly on every terrain.
What Is Shock Length?
Shock length refers to the eye-to-eye distance between the mounting points of a shock absorber. Shocks also have a stroke length, which is the amount the shock shaft compresses during suspension travel.
There are two important values to know:
- Eye-to-eye length: Distance from the center of one mounting eye to the center of the other when fully extended.
- Stroke length: How much the shock compresses from full extension to full compression.
Knowing these values allows you to match the shock to your suspension design, ensuring correct sag, travel, and bottom-out protection.
Why You Need a Shock Length Calculator
Choosing a shock absorber thatโs too long or too short can cause:
- โ ๏ธ Suspension binding or over-extension
- โ ๏ธ Bottoming out and damaging components
- โ ๏ธ Poor ride quality and unsafe handling
The Shock Length Calculator removes these risks by providing accurate shock length values based on your desired suspension travel and linkage ratio. Itโs useful for:
- ๐ดโโ๏ธ Mountain bikes
- ๐๏ธ Motorcycles
- ๐ Cars
- ๐ป ATVs and UTVs
- ๐๏ธ Race vehicles
- ๐ ๏ธ Custom builds and restorations
Formula Behind the Shock Length Calculation
The basic relationship between shock stroke and wheel travel is based on the leverage ratio (LR): Wheel Travel=Shock StrokeรLeverage Ratio\text{Wheel Travel} = \text{Shock Stroke} \times \text{Leverage Ratio}Wheel Travel=Shock StrokeรLeverage Ratio
Rearranged to find shock stroke: Shock Stroke=Wheel TravelLeverage Ratio\text{Shock Stroke} = \frac{\text{Wheel Travel}}{\text{Leverage Ratio}}Shock Stroke=Leverage RatioWheel Travelโ
Once you know the stroke, you can find the eye-to-eye length by adding the stroke to the compressed shock body length. Most shocks have standard ratios of eye-to-eye vs stroke, for example:
| Eye-to-Eye (mm) | Stroke (mm) |
|---|---|
| 165 | 38 |
| 190 | 51 |
| 200 | 57 |
| 216 | 63 |
| 222 | 70 |
| 241 | 76 |
The calculator automates this by letting you input wheel travel and leverage ratio to instantly get the ideal shock stroke and eye-to-eye length.
How to Use the Shock Length Calculator
Follow these simple steps to get accurate results:
Step 1 โ Enter Desired Wheel Travel
- Type the total rear wheel travel you want (e.g., 150 mm for a trail bike)
- Make sure to use millimeters or inches consistently
Step 2 โ Enter Suspension Leverage Ratio
- Enter your frameโs average leverage ratio (commonly between 2.0 and 3.5)
- If unsure, check the manufacturerโs specs or measure linkage geometry
Step 3 โ Click Calculate
- The calculator instantly outputs:
- Required shock stroke
- Recommended eye-to-eye shock length
Step 4 โ Install or Purchase the Correct Shock
- Choose a shock model that closely matches the recommended specs
- Check frame clearance and mounting hardware compatibility before installation
Practical Example
Goal: Set up a mountain bike with 150 mm of rear travel and a 2.7 leverage ratio.
Step 1: Calculate Stroke Shock Stroke=1502.7โ55.5 mm\text{Shock Stroke} = \frac{150}{2.7} \approx 55.5 \text{ mm}Shock Stroke=2.7150โโ55.5 mm
Step 2: Estimate Eye-to-Eye Length
- Based on standard shock sizing charts, a 55.5 mm stroke pairs well with a 200 mm eye-to-eye shock.
โ Result: Use a shock that is 200 mm eye-to-eye with 55 mm stroke.
This ensures the frame gets the full 150 mm of travel without bottoming out or topping out.
Common Applications
The Shock Length Calculator is ideal for:
- ๐ดโโ๏ธ Mountain bike rear shocks
- ๐๏ธ Motorcycle rear mono shocks
- ๐ป Off-road truck and UTV suspension tuning
- ๐๏ธ Race car coilover setups
- ๐ ๏ธ Custom vehicle projects
- โ๏ธ Suspension geometry design
Any system that uses a shock absorber connected via a linkage can benefit from this calculator.
Features of the Shock Length Calculator
- ๐ Calculates stroke and eye-to-eye length
- โก Instant, accurate results
- ๐ฑ Works on mobile, tablet, and desktop
- ๐ Copy or export result
- ๐ฏ Based on standard leverage and travel formulas
- ๐ก Simple interface with just two inputs
Benefits of Using This Tool
- โ Eliminates guesswork from shock selection
- โ Prevents frame damage from incorrect shock sizing
- โ Improves ride quality by ensuring correct sag and travel
- โ Saves money and time on trial-and-error purchases
- โ Helps plan custom suspension builds
Tips for Accurate Shock Length Calculation
- Measure actual wheel travel, not just frame movement
- Use the average leverage ratio (or progressive chart if available)
- Ensure mounting hardware matches shock eyelet size
- Leave a small safety margin for suspension sag and clearance
- Double-check frame manufacturer recommendations
FAQ โ Shock Length Calculator
Here are 20 common questions and answers:
1. What does this calculator do?
It calculates the ideal shock stroke and length based on wheel travel and leverage ratio.
2. What inputs are needed?
Desired wheel travel and average leverage ratio.
3. What is leverage ratio?
The ratio of wheel travel to shock stroke.
4. How do I find my leverage ratio?
Check your frame specs or divide wheel travel by shock stroke.
5. Can I enter inches instead of millimeters?
Yes, as long as all values use the same unit.
6. What is eye-to-eye length?
The distance between shock mounting holes when fully extended.
7. What is stroke length?
How far the shock shaft moves during compression.
8. Can I use this for mountain bikes?
Yes, itโs perfect for MTB suspension design.
9. Can I use this for motorcycles?
Yes, it works for any shock-based suspension.
10. Will this work for cars?
Yes, it helps size coilover shocks and dampers.
11. What happens if my shock is too short?
Youโll lose travel and affect suspension geometry.
12. What happens if my shock is too long?
You risk bottoming out, frame damage, and unsafe handling.
13. Does this tool consider sag?
No, calculate sag separately (usually 25โ30% of travel).
14. Does this tool consider spring rate?
No, it only calculates geometry, not stiffness.
15. Can I input fractional leverage ratios?
Yes, like 2.65 or 2.85.
16. What are common leverage ratios?
Most bikes use 2.0โ3.5, motorcycles often 2.5โ3.0.
17. Can I use this for linkage forks?
Yes, as long as you know travel and ratio.
18. Is this accurate?
Yes, it uses the standard suspension formula.
19. Is this calculator free?
Yes, completely free to use.
20. Can I use this on mobile?
Yes, itโs fully mobile-friendly.
Final Thoughts
The Shock Length Calculator is an essential tool for anyone setting up or modifying a suspension system. It makes it simple to find the correct eye-to-eye length and stroke to match your desired wheel travel and leverage ratio.