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Sag

The amount a suspension compresses under the rider's weight when sitting in a neutral riding position.

Published January 1, 2025

Definition

Sag is the percentage of total suspension travel that compresses under the rider's static weight — including riding gear, helmet, pack, and any carried water — when sitting on the bike in a neutral riding position. It is the foundational adjustment of any suspension setup, set before any damping adjustments are made.

How It Works

When you sit on a bike, gravity compresses the suspension springs. The amount of compression relative to the total available travel is expressed as a percentage. A fork with 160mm of travel that compresses 32mm under rider weight has 20% sag.

Sag serves two purposes. First, it positions the suspension in the middle of its working range so it can extend (for traction over compressions) as well as compress (for absorbing impacts). Second, it sets the effective spring rate — more sag means a softer effective spring, less sag means a firmer one.

If sag is too low, the suspension sits too high in its travel, reducing the ability to extend into compressions and causing a harsh, deflecting ride. If sag is too high, the bike wallows, uses travel prematurely, and handles poorly through repeated hits.

Recommended Values

Manufacturer recommendations vary, but common starting points are:

  • Fork: 15–20% of travel
  • Rear shock: 25–30% of travel

Cross-country and XC race setups often run less sag (15–20% rear) for efficiency. Enduro and downhill riders frequently run more (30–35%) for better small-bump sensitivity and traction.

How to Set It

  1. Install an O-ring or zip tie on the fork stanchion or shock shaft
  2. Wearing all riding gear, mount the bike and assume a neutral riding position
  3. Carefully dismount without compressing the suspension further
  4. Measure the distance the O-ring traveled from its starting position
  5. Divide that measurement by total travel and multiply by 100 for the percentage
  6. Adjust air pressure (air spring) or preload (coil spring) accordingly — more pressure reduces sag, less pressure increases it

When measuring rear shock sag, use manufacturer recommendations as a starting point and always perform the measurement the same way — sitting or standing — as the percentage differs considerably between the two positions.1

Some forks and shocks have sag indicator windows or markings on the stanchions to simplify the process.2

See Also

References

Footnotes

  1. Enduro MTB Magazine, "Sitting or Standing? How to Setup MTB Suspension Sag Correctly" https://enduro-mtb.com/en/sitting-standing-mtb-sag/ ↩

  2. BikeMag, "Mountain Bike Suspension Setup: The Complete Guide" https://www.bikemag.com/how-to/mountain-bike-suspension-setup ↩