The forces on a pulley are not the same according to the angle at which the pulley works. This is called the load factor.
The worst thing for a pulley is to pull the load to be mounted in parallel (for example, a pulley placed at the mast head for a halyard).
Let us take again the example of the halyard pulley. If I pull on one side at 100 kg to lift the mainsail, which also weighs 100 kg - for the example, we don't consider the friction - the pulley holds 200 kg, which is a load factor of 200%.
On the other hand, a 45° deflection has a load factor of 75% (if I pull 100 kg, the pulley only loads 75 kg).
Below is the table showing the load factor (in %) as a function of the defection angle (in °)
| defection angle | load factor |
| 180° | 200% |
| 160° | 197% |
| 140° | 187% |
| 120° | 180% |
| 100° | 153% |
| 90° | 140% |
| 80° | 129% |
| 60° | 100% |
| 45° | 75% |
| 20° | 35% |
| 0° | 0% |
