Velopedia Tools

Suspension Setup

Sag Calculator & Tuning Guide

Turn fork and shock measurements into usable setup targets. Calculate sag in millimeters, compare measured sag with the target, evaluate front-to-rear balance, and get tuning direction without assuming that one rider weight equals one universal air pressure.

Starting target

Choose a baseline, then adjust the percentages for your bike and preferences.

Ride profilePresets are starting targets, not manufacturer specifications Fork target sag % Rear target sag %

Fork

Measure from the dust wiper to the sag O-ring after settling into your normal riding position.

Fork travel mm Spring type Measured sag mmLeave blank to calculate target only Current pressure psiRecorded for your setup sheet; not used to invent a target PSI

Rear suspension

Rear sag percentage is measured at the shock stroke; wheel sag is shown separately.

Rear wheel travel mm Shock stroke mm Spring type

Measured shock sag mmMeasure movement at the shock shaft/body, not at the rear wheel Current pressure psiRecorded only; always observe the shock's published pressure limit

Ride feedback

Optional: choose the main symptom you are trying to correct.

Primary symptom

Why this calculator starts with sag—not PSI

Air pressure is component-specific. Two forks under the same rider can require different pressures because piston area, negative-spring design, travel, chassis configuration and manufacturer tuning differ. The measurable setup target is sag: how far the suspension settles into its travel with the rider aboard. Use your fork or shock manufacturer's pressure chart as the first pressure estimate, then adjust to the intended sag.

Sag % = measured sag ÷ available travel × 100Target sag (mm) = travel or shock stroke × target sag %

Fork sag and shock sag are different measurements

Fork

Fork sag is measured directly against fork travel. A 150 mm fork at 20% sag has a 30 mm target measurement.

Rear shock

Rear sag percentage is normally measured against shock stroke, not rear-wheel travel. A 55 mm stroke at 30% sag is 16.5 mm at the shock.

Rear wheel

Wheel sag can be estimated from rear-wheel travel × sag percentage, but the shock measurement is the practical setup reference because frame leverage changes through the stroke.

Balance

Front and rear do not need identical sag percentages. Balance means both ends support the intended riding position and work together through the terrain.

Spring first, damping second

Establish spring pressure or coil rate and sag before chasing damping settings. If sag is correct but bottom-out resistance is insufficient, compatible air-spring volume spacers can increase end-stroke progression without using excess pressure simply to prevent bottoming. If the suspension packs on repeated impacts, rebound may be too slow; if it kicks back aggressively, rebound may be too fast. Compression adjustments are best made after spring support and rebound are reasonably settled.

What the presets mean

The profile presets are Velopedia starting points inside commonly published manufacturer ranges, not rules for a specific product. Current FOX fork documentation commonly specifies roughly 15–20% sag, while FOX and RockShox rear-shock guidance commonly places sag in the high-20% to low-30% range. Frame manufacturers may specify a particular value because suspension kinematics are designed around a specific ride height; use that value when provided.

Setup references: RockShox Suspension Welcome Guide · RockShox Fine Tuning · FOX Bike Tech Help Center