Dirt Bike Sag Calculator

To calculate dirt bike sag, you need to determine race sag and free sag using the following formulas:

1. Race Sag Formula

Race sag is how much the suspension compresses when the rider is on the bike. Race Sag=Bike Unloaded−Bike Loaded (with rider)\text{Race Sag} = \text{Bike Unloaded} – \text{Bike Loaded (with rider)}Race Sag=Bike Unloaded−Bike Loaded (with rider)

2. Free Sag Formula

Free sag is how much the suspension compresses under the bike’s own weight, without the rider. Free Sag=Bike Unloaded−Bike Loaded (no rider)\text{Free Sag} = \text{Bike Unloaded} – \text{Bike Loaded (no rider)}Free Sag=Bike Unloaded−Bike Loaded (no rider)

Steps to Measure:

  1. Bike Unloaded (A): Measure from the rear axle to a fixed point on the fender with the bike on a stand (wheel off the ground).
  2. Bike Loaded (no rider) (B): Measure the same point with the bike on the ground, under its own weight.
  3. Bike Loaded (with rider) (C): Measure with the rider fully geared up in a natural riding position.

Example Calculation

  • A (Unloaded): 600mm
  • B (Bike only): 580mm
  • C (Bike + Rider): 520mm

Race Sag

600mm−520mm=80mm600mm – 520mm = 80mm600mm−520mm=80mm

Free Sag

600mm−580mm=20mm600mm – 580mm = 20mm600mm−580mm=20mm

Recommended Sag Settings

  • Race Sag: ~30-35% of total suspension travel (usually 90-105mm for dirt bikes).
  • Free Sag: ~5-10% of total travel (typically 25-45mm).

If the race sag is too high → Increase preload.
If the race sag is too low → Decrease preload.