Tree Work
Mechanical Advantage Calculator
Add friction and see what your rigging actually gives you. A "3:1" system loses about 15% per pulley to friction, so real-world MA at the haul is closer to 2.2:1.
Real pull force required (lb)
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- Theoretical pull (lb)
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- Real MA achieved
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- System efficiency
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FAQ
Why is real MA less than theoretical? +
Every sheave (pulley wheel) eats some of your input force to friction and rope deformation. Quality bearings give 92-95%; cheap or dirty pulleys can be 75% or less.
When is a 3:1 worth it? +
Any time you cannot pull the static load with body weight. A 200 lb climber on a 3:1 can move ~500-600 lb of real load through clean pulleys.
Compound vs simple systems? +
A compound system multiplies advantages but also stacks friction losses. A 9:1 compound (3:1 × 3:1) gives about 6.4:1 real-world advantage at 85% pulleys.