Fork Oil Level

How Oil Level Affects Bottom-Out Resistance

  1. Air Spring Effect
    • The space above the oil in the fork is filled with air, which acts as a secondary spring.
    • As the fork compresses, this air volume gets squeezed, increasing internal pressure and resisting further compression.
  2. Higher Oil Level = More Bottom-Out Resistance
    • Raising the oil level reduces the air volume, making the air spring ramp up more aggressively.
    • This means the fork resists bottoming out more effectively without needing stiffer springs.
    • Useful for aggressive riding or big impacts.
  3. Lower Oil Level = Less Bottom-Out Resistance
    • A lower oil level increases the air volume, making the air spring effect more gradual.
    • The fork compresses more easily, and bottoming out can happen sooner if the damping and spring rate aren’t sufficient.
    • Preferred for a more plush ride over small bumps.
  4. Effect on Damping
    • The oil level does not directly affect damping (which is controlled by valving, but it indirectly influences the overall feel by modifying how the fork handles the last part of its travel.

Tuning Considerations

  • Riders looking for more bottom-out resistance can increase the oil level rather than changing fork springs or damping settings.
  • Too much oil can cause hydraulic lock, where the fork becomes excessively stiff and harsh before full compression.
  • Too little oil can result in frequent bottoming out and reduced support.