Suspension 101: Part II - Volume Spacers

A handful of volume spacers from Rockshox and Fox

So, you’ve read Part I of this series and after a bit of fettling your spring rate is set just right and hopefully, your bike is feeling better than ever. Let’s dive a little deeper into the dark art of suspension setup, this time focusing on volume spacers, otherwise known as tokens. If you want to catch up, check out Part I HERE.

You’ll know already from Part I of this series that the air spring pressure of your suspension is what determines how hard or soft it feels. A higher pressure gives a firmer spring rate and vice versa for a lower pressure. In Part I we were focusing on setting the overall spring rate for your suspension, in this article we are going to look at how you can use volume spacers to tune the spring rate of your suspension as it compresses through its travel. 

Tomy inflating his Rockshox Zeb Ultimate using a digital shock pump

A volume spacer, as the name implies, is a little piece of plastic that takes up space inside your fork or shock’s air chamber. As you decrease the volume of a gas container, in this case your suspension, the overall pressure of the system increases; this is described in Boyle’s Law as P₁V₁=P₂V₂ if anyone fancies dipping their toe into the world of Thermodynamics. 

So, if you reduce the volume of your suspension’s air chamber by adding a volume spacer, as it goes through its travel the pressure will increase quicker than if the volume spacer was not installed. This gives the feeling of the suspension getting firmer as it goes deeper into the travel, a feeling known as progression. Volume spacers most noticeably increase the progression of your suspension from about 50% travel onwards, the further through the travel you go, the more effect the volume spacer has.

A sketch of a graph showing shock progression with and without volume spacers

At this point it’s worth noting that differences in frame layouts mean that some rear suspension designs are inherently more progressive than others. What this means in the real world is that a more progressive frame will need fewer volume spacers to achieve the same rear suspension feel as a less progressive (more linear) frame. Forks are unaffected by frame design so your preferred fork setup will feel the same on any frame design. 

Hopefully now we understand what volume spacers are and how they affect your suspension, but how do you know when to add, or remove, volume spacers? Broadly speaking, if you’re bottoming out your suspension easily, add a spacer. If you’re struggling to reach close to full travel, remove a spacer. However, as you may have gathered by now, there is far more to learn. 

1 volume spacer installed in this Rockshox Zeb Ultimate

Volume spacers can be used to adjust bottom out resistance as well as tuning the ride height of your fork or shock. As an example, a rider might be running 60psi with 2 volume spacers installed, giving a decent spring rate and resisting bottom out well. However, in the search for a more forgiving ride over smaller bumps, they might decide to try running 3 volume spacers and drop down to 55psi. This reduced air spring pressure would mean they are running more sag on the fork while the extra volume spacer adds progression to account for the drop in air pressure. 

Adding a second volume spacer to the Rockshox Zeb Ultimate

For the most part, adding just one volume spacer makes quite a noticeable change to the feel of your fork or shock. Too few will feel like the fork dives quite easily through its travel, whereas too many and you’ll feel as though you hit a wall of progression that you can’t push past, meaning you never reach close to full travel. 

As you did after setting your air pressures, write down your setting before making any changes so you can easily revert back to your original setup. 

0psi in this Rockshox Zeb Ultimate

How to fit volume spacers in a Rockshox or Fox fork:

  1. Completely de-pressurise your fork, using a shock pump to release the high pressure air. Once the shock pump reads 0psi, remove it and push the valve core gently with a 4mm allen key, just to make sure there’s no air remaining. 
  2. Remove the air side top cap. Rockshox forks use a standard cassette tool, Fox use a 32mm chamferless socket (make sure it’s a chamferless socket, a regular socket will make a mess of your top cap).
  3. Fit/remove your desired number of volume spacers. Rockshox volume spacers screw into one another, Fox ones slide and snap into place. 
  4. Reinstall your top cap, torquing down to the manufacturer's specification.
  5. Re-inflate to your desired pressure. 
  6. Write down your new settings and go ride

Removing the top cap on the Rockshox Zeb Ultimate

Once you’re confident in adding or removing spacers, experiment with your setup. How does adding a spacer and dropping air pressure change your ride? Do you prefer a higher spring pressure with fewer spacers or a lower pressure with more spacers? There are no wrong answers here and only trying new things and finding what works best for you will help you find your ideal setup. 

Tomy torquing up the top cap on the Rockshox Zeb Ultimate

If this has got you more interested in your suspension setup and you want to maximise your bikes performance on trail, consider a suspension setup day with TVB Tech. We offer professional suspension setup days with our World Cup level data logging equipment to help you dial in your ideal setup, helping increase confidence and control. 

Rockshox and Fox volume spacers

01896 831 429

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