SAG Calculator
### Motorcycle & Mountain Bike Suspension Physics **Suspension Sag** is the amount of compression that occurs in a motorcycle fork, shock, or mountain bike suspension solely due to the static weight.
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📐 Formula
💡 Practical Example
Setting up a 150 mm travel mountain bike with 600 mm unweighted eye-to-eye length: When sitting in attack position with full gear, the shock compresses to 555 mm. Sag is 45 mm (30%), the ideal threshold for trail traction and pedaling efficiency.
📖 About SAG Calculator
Motorcycle & Mountain Bike Suspension Physics
Suspension Sag is the amount of compression that occurs in a motorcycle fork, shock, or mountain bike suspension solely due to the static weight of the rider in full gear.
Primary Suspension Sag Formulas
- Measured Sag Distance: Sag (mm) = M_1 - M_2
- Sag Percentage of Stroke: Sag (\%) = ((M_1 - M_2) / (Total Stroke Travel)) × 100
- Remaining Usable Travel: Travel_rem = Total Travel - Sag (mm)
Recommended Sag Percentages by Discipline
- XC (Cross-Country MTB): 20\% - 25\% (Firm, high pedaling efficiency, climb support)
- Trail / All-Mountain: 25\% - 30\% (Balanced compliance, cornering grip, pop)
- Enduro / Downhill (DH): 30\% - 35\% (Plush traction, high-speed rock absorption)
- Street Motorcycles: 25\% - 30\% (30 - 40 mm of total stroke)
- Motocross Dirt Bikes: 30\% - 33\% (100 - 108 mm race sag)
How to Use This Calculator
Enter your Total Suspension Travel / Stroke (mm) (e.g. 150 in mm), Unloaded Extended Measurement (M1 - mm) (e.g. 600 in mm), Loaded Rider Sag Measurement (M2 - mm) (e.g. 555 in mm), and Riding Discipline / Target Setup — choose from XC Cross-Country MTB (20% - 25% Sag), Trail / All-Mountain MTB (25% - 30% Sag), Enduro / Downhill MTB (30% - 35% Sag). Results update instantly as you type — adjust any value to compare scenarios.
Worked Example
Setting up a 150 mm travel mountain bike with 600 mm unweighted eye-to-eye length: When sitting in attack position with full gear, the shock compresses to 555 mm. Sag is 45 mm (30%), the ideal threshold for trail traction and pedaling efficiency.
Understanding Your Result
Evaluate your result in the context of your specific use case and relevant industry standards or reference values. A single calculated result is a starting point — test two to three scenarios to understand how sensitive the outcome is to your key input assumptions. For high-stakes decisions, verify your result against a secondary source or subject-matter expert before acting.
💡 Mathematical Rigor & Applied Context
- This calculator applies exact mathematical definitions following conventions established by NIST and international standards bodies.
- Rounding errors accumulate across multi-step calculations. For precision-critical work, maintain extra significant figures through all intermediate steps.
- Many mathematical concepts have multiple valid formulations — if a result seems unexpected, verify which convention or definition applies to your context.
- Dimensional analysis (unit tracking) is the fastest way to catch formula errors. Every term in an equation must have consistent, compatible units.
- Numerical methods used in digital calculators introduce floating-point precision limits (~15 significant digits for IEEE 754 double precision).
- For statistical and probabilistic calculations, always specify whether you are working with population parameters or sample statistics — formulas differ.
- Visualizing a problem geometrically or testing with known boundary values (zero, infinity, negative) reveals hidden errors faster than algebraic checking.
- When in doubt, validate your result against a simplified hand calculation or a published worked example from a textbook or standards document.
Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.