Rear Shock information to cram into your brain hole!
Here you are, probably wondering, "what the heck do these numbers on my rear shock mean?" Pedal Driven Co is here to tell you so you can sound like captain know-it-all at your next shred session with your homies. Whether it's comparing the length of your eye-to-eye or whose stroke length is the longest, we're here to help.
Main Shock Information
There are three main specifications that dictate shock sizing and frame compatibility. For the most part, none of these specifications are interchangeable on any given platform, save for the very few frames that are designed to work with different shock measurements.
The metric standard was created to cut down the number of shocks that manufacturers have to produce and make it simpler for all of us when purchasing new or upgraded shocks.
If you inspect your shock, you'll see you may have the physical size printed directly onto the shock, or a Tune ID, Shock Code, etc that will allow you to look up all the pertinent information regarding your shock on the manufacturer's website. In some cases, your shock may have neither, and that's ok, because we'll walk you through the basics and how to measure them yourself below!
• Shock Eye to Eye Length - This is the length of the shock and determines the distance between the mounting holes when at full extension. Measured from center of eyelet to center of eyelet.
• Shock Stroke Length - This is the measurement of how far the shock can travel from full extension to full compression. This determines how far the shock can travel and does not directly correlate to a bike frames rear travel measurement.
• Shock Mounting Interface - This is the interface or mounting type of the shock and dictates how the shock is attached to the frame.
Eye to Eye Length
Measuring a Shocks eye-to-eye length is simple. Some shock specifications are in Imperial shown as inches while others are Metric shown as Millimeters. You can measure a shocks eye-to-eye length by measuring from the centerline to centerline of the mounting eyelets/openings. This measurement is frame specific and can not be interchanged.
Stroke Length is the maximum amount of travel that a shock can move through its range. This is the difference in the length of a shock as measured from its eye-to-eye at full extension and subtracting the shocks length from eye-to-eye at full compression. For instance, if you've got a shock that has a eye-to-eye of 205mm when fully extended, and an eye-to-eye length of 145mm when fully compressed you have a Stroke Length of 60mm.
Stroke Lengths on Metric sized shocks come in 2.5mm increments. This length is standardized, such that any shock with an identical eye-to-eye and mounting interface are able to be adjusted. So a 205mm eye-to-eye shock in a 65mm stroke is the same as a 60mm stroke just with two 2.5mm spacers added.
**Warning!** Do not increase your shocks stroke length past the frame manufacturer's listed maximum as this will cause frame clearance issues that can damage or destroy your frame. Some Frame manufacturers do allow you to increase or decrease stroke length, however, this is uncommon.
Shock Mounting Interface
When it comes to attaching your shock to your bike's frame mounting locations, there are two types of interfaces. One being a Traditional or "Standard" mounting interface and the other being a more compact Trunnion mounting interface.
Trunnion mounting (Upper shock in photo above) is configured in such a way that provides a more compact mounting solution where the mounting interface is integrated into the top of the shock. This interface has a mounting bolt on either side.
Standard mounting (Lower shock in photo above) is seen where the top or side of the shock where the body of the shock has a mounting interface that is extended or proud of the top of the stationary portion of the shock. This interface typically has a through bolt with spacers.