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Rear Shock Hardware Sizing Explained

In this article we'll help you make sense of the sizes, mounting options, bushing and hardware sizes for the most popular shocks.

Metric Vs Imperial Sizing

The sizing of your shock can be broken down in to two measurements, Eye to eye and stroke. The Eye to eye is measured from the centre of the bolt hole at full extension and the stroke is the length of travel the shaft of he shock has to move when compressed.

Most new bikes and shocks are now metric, this has widely been adopted as the new way to measure rear MTB shocks. You'd normally expect this to look like 230x65mm or 185x45. Older shocks might be 7.875" x 2.0", you might still find imperial shocks but they're becoming more and more rare as time goes by.

This change meant that shock manufacturers could make fewer sizes of shock and change the size of the stroke via spacers. That's why you'll often see a 230 x 65 shock which might be the same body as a 62.5mm and 60mm. This is a great change for both consumers and the manufacturer as you can often change the travel to suit different bikes.

Can I change the travel on my shock? Yes you can but there are considerations to make, Fox and older Rockshox shocks are fairly simple. The newer Rockshox shocks with Hydraulic bottom out need to be rebuilt to get the same effect. 

Trunnion vs Standard

Trunnion shocks feature the top mounting bolts screwed directly into the head of the shock, this is used to lower the overall length of the shock and make it easier for frame designers to get the shock into more compact areas. As these don't use normal bushings for rotation you'd normally expect to see them bolted to a bearing in a link or on the frame.

Standard mounts protrude from the top of the shock and feature a more conventional bushing and bolt situation. 

Bearing Ends

Some frames will feature bearings on the end of the shock, this can spread the forces more evenly and make the movement of the shock smoother. Is it better? We're not sure but the brands that use it certainly think so. RockShox shocks can't be changed without modification, Fox normally uses a 30x8mm push in bearing. It's easy to forget to look after these and they can get pretty crusty if you don't take them out for servicing regularly.

Hardware Measuring

How do I measure the hardware on my shock? The first and easiest way to work this out is to search your bike online and find the sizes in the tech docs. Brands like Santa Cruz do it very well but you might have to do a bit of hunting.

If you can't find it you can find out with these measurements:

  • Bolt diameter: Use a set of callipers to measure the bolt diameter, normally 6, 8 or 10mm.
  • Width: The total width of the mounting hardware, make sure to include any spacers.
  • Eyelet diameter: The internal diameter of the shock eyelet where the hardware fits. Typically 12mm, 12.7mm or 1/2". (Inside the bushing)

This will give you the sizing, you can buy brand specific hardware if you have a shock from the major brands if they are in stock!

Where to Buy

There are a few good options out there, where possible go with the brands own hardware but we've used other options with great success.

Please note that Marzocchi and Fox use the same sizing and hardware.

Spares and Wearable Parts

Something we find all too often is a worn shock bushing, they are a wearable part and due to their location its not always the first thing you think of when your bike develops a rattle. If it can move then its likely making a mess of you hardware, your shock or wearing it's way in to your expensive frame.

They're easily changed and you can find the most common spares here:

Tools. It can be tempting to use a hammer and a punch or a vice but it'll definitely be more expensive to take it to a bike shop to get a bent bolt out. Consider getting the right tools for the job.

Where to find more info

Most big brands have a vast library of information available, we've put some of the more popular links here:

At Biketart we're proud to have a dedicated tech team at your disposal, if you need to buy something and you need help, pop us a message on the chat or email us here.