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:
- 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).
- Bike Loaded (no rider) (B): Measure the same point with the bike on the ground, under its own weight.
- 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.