This is the “advanced spring rate estimator.” Using this allows you to get a feel for what spring is appropriate for your bike and rider weight. You must enter information in all fields to get a result, the result is an estimation of sag, wheel rate, sag percentage, and sprung weight of the back of the bike. If you don’t have the information available to fill out the advanced estimator the regular spring rate estimator might be a better resource.


Enter your weight, your bike’s weight, spring rate, built in preload, total damper travel, and motion ratio. The form will calculate the rest.

Calculation Formula

(((Rider weight) + (Bike Weight)) * (Weight Distribution)) – (Unsprung Weight) = Total Sprung Weight at Rear

(Spring Rate) * (2) = Total Rear Spring Rate

(Distance 1) / (Distance 2) = Motion Ration | This calculation is done with Distance 1 equalling 1 unit, Distance 2 is the amount of spring compression after Distance 1 has traveled 1 Unit.

(Spring Length at Full Damper Extension in Inches) – (Spring Free Length in Inches) = Total Spring Compression Before Loading

(Total Spring Length Compression) * (Spring Rate) * (2) = Total Spring Force at Damper Full Extension

(Spring Rate) * (Motion Ratio) = Wheel Rate | Non-linear motion ratios complicate this, measure motion ratio at or near laden sag distance.

((Load On Rear Suspension) – (Total Spring Compression Before Loading))/ (Wheel Rate) = Approximate Sag

Warning and Caveats

Non-linear motion rations are not accounted for.

Chain pull is not factored.

Anti-squat is not factored.