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Suspension & Setup

Fork Spring Rate Calculator

Two fork springs share the front load. Convert between N/mm and lb/in, or size springs from rider weight and target sag.

Inputs
Results
Live

  • Suggested rate (each leg)

    1.98N/mm

  • Suggested rate

    11.31lb/in

  • Combined fork rate

    3.96N/mm

  • Vs current spring

    -55.0%

    Consider a softer fork spring

Formula

k_each = (front load) / (2 × sag)

Related calculators

Sag
Sag is how far the bike settles from fully extended. Measure from a fender mark to the axle with the bike on a stand, then on the ground.
Race Sag
Race sag (rider sag) is measured with the rider in full gear, balanced on the pegs. Most MX bikes want about 100–108 mm on ~310 mm travel.
Rider Sag
Front and rear rider sag together. Enter fender-to-axle (or a zip-tie on the fork stanchion) for each end.
Static Sag
Static sag is bike-only, no rider. Too little static sag with correct race sag means the spring is too soft (you used a lot of preload). Too much static sag means the spring is too stiff.