How to measure a bike for a shock absorber

Written by aden williamson
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How to measure a bike for a shock absorber
(mountain bike downhill image by Maxim Petrichuk from

A bike shock absorber, usually just referred to as a shock, mounts onto a suspension frame and provides for rear suspension on a bike. Although in theory any style of bike could have rear suspension, in practice it is mainly mountain bikes which have this feature. There are many different rear shocks on the market for the many different types of bikes and riders out there. And each shock model comes in multiple sizes. To know which size shock your bike requires, you must find the eye to eye, stroke and diameter measurements.

Skill level:
Moderately Easy

Things you need

  • Tape measure

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  1. 1

    Use the tape measure to find the length, or eye to eye, measurement. If you are replacing an existing shock, measure it from the centre of the eyelet on one end to the centre of the eyelet on the opposite end. If there is no existing shock, measure the distance between the mounting point on the main triangle of the bike frame and the mounting point on the linkage connected to the rear triangle of the frame. Common eye to eye lengths are between 6 inches and 9 inches.

  2. 2

    Find the maximum allowable diameter of the shock by measuring the space available on the axis opposite that of the two shock mounting points. Be aware that shocks meant for long-travel freeride and downhill bikes often have a piggyback reservoir, which requires additional clearance depending on the specifics of the shock. The shock diameter must be smaller than the maximum permitted by your frame.

  3. 3

    Determine the shock stroke by measuring the shaft on the existing shock. The shaft is the part that actually compresses into the shock body. If there is no existing shock, check how far the eye to eye length between the front triangle and rear triangle mounting points is shortened when your rear wheel rises the maximum travel for that bike frame. For instance, if the eye to eye length is eight inches and the frame is supposed to have seven inches of travel, raise the rear wheel exactly seven inches and measure the eye to eye length again. The amount by which the eye to eye was reduced is equal to the stroke. The stroke is written after the eye to eye, for example as 9.0" x 2.0" for a nine inch shock with a two inch stroke.

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