Tech Talk: Tuning Air Forks With Tokens

Tech Talk: Tuning Air Forks With Tokens

When RockShox introduced the revamped Pike, they brought with it Air Tokens. They were not the first to allow you to adjust the air volume of their forks, but they were the first to make it mainstream. Those innocuous looking little red plastic blobs that shipped with your fork started a revolution. 2 years on, the little red blobs are grey, and pretty much every manufacturer has something doing something similar in their forks now, but what are they for and why should you care?

Second time luckier. The Pike Mk2 was the one that changed it all.

Why Should I Care?

You should care because if you’ve not messed around with the air tokens in your fork, you’re probably not getting the best performance you could. Its a very cheap and easy way of transforming your suspension to behave in a way that suits you and your riding style, without the expense of custom tuning.

How an Air-Spring Works

To understand what the tokens can do for you, we need to first understand how an air spring works. A normal* coil spring exhibits behaviour known as being linear. What this means is that the spring inside a coil fork will require the exact same force to move it 10% of its travel whether its at the start or end of its travel. On the other hand, an air spring exhibits whats known as progression. Progression means that the air spring will require less force to move it 10% of its stroke at the start of its travel than the end. There are other forces at work such as stiction (STatic frICTION) and damping, but the spring is the basic mechanism of making your forks bounce, and so deserves your attention.
* Progressive coil springs do exist, achieved through using variable coiling, but we’ll not worry about that now.
To put that in simple terms, imagine you are loading weights onto the ends of your bars to compress your forks. You might need 100KG to compress a fork from 0% of available travel to 50% of its travel, but you might then need 200KG to get through the second half of the forks travel. So you needed 300KG of weight on the bars to get from fully extended to fully compressed, but:
100KG of that got you half way 200KG might have got you 4/5ths through The final 1/5th of the travel needed another 100KG In practice what this means is that the deeper into your travel you get, the more the forks resist compression. Useful to prevent big bumps eating too much travel when you have nice small bump compliance, and vice versa useful to prevent you having to run too much air in order to hold the forks up, killing your small bump sensitivity.

What Do the Tokens Do?

Tokens reduce the volume of air inside your fork. This links to the important concept that the increase in spring rate (the progressiveness of the air spring) relates to the reduction in its volume as it compresses, in relationship to its total volume. Sounds complicated? Its not so bad. What it means is that the progression is relative to how much you reduced the volume by as a percentage, not the actual volume lost. So we think of 50% of the air spring volume, not 50 cubic centimetres.
The tokens take up space that would other wise be filled with air, and hence part of the air spring. Say your fork had 100mm of travel. With no tokens in, using all your travel might have used 60% of the available air volume, squeezing all the air into the remaining 40% space. If you added a couple of tokens, the fork might now use 80% of the available air volume in compression, squeezing the air into the remaining 20% of space. Its this adjustment in the relative volume of the air spring that changes to progressiveness of the fork.

May the Force be with you, and progressive.

My Forks Have Tokens in From The Factory. So I’m Done Right?

Probably not. The factory installed tokens are there to adjust the base spring volume from what it would be at the forks maximum possible travel version, to the one you have bought. By adding tokens, the manufacturer is attempting to correct the air spring progression so its roughly the same feel whether your fork is 120mm, or 180mm travel. Put another way, without a good slug of tokens a 120mm fork would blow through its travel so easily it would be basically useless, assuming of course it is a RockShox 120mm fork based on a 180mm chassis like a Lyrik or Yari. With each step down in travel (10 or 20mm) the manufacturer will add another token to compensate for the air volume, but that doesn’t mean its right for you.

When Should I Use Tokens?

This is the million dollar question, and the one to which there is no real definitive answer, but here’s some useful guides as to when tokens might be needed, or maybe need to be removed**.
Scenario 1: You set your sag properly, and the forks feel great on the small stuff, but even moderate trails, rollers and berms are using all of the travel in the fork. Solution: Add token(s) & maintain fork pressure. Scenario 2: You’ve got the forks running sweet when they are deep into their travel, holding you up well and using their travel at just the right rate, but they feel harsh on the small stuff, and the bar buzz is killing you. Solution: Add token(s) & drop fork pressure.
Scenario 3: Your forks feel great at the start of the stroke, but you’re rarely reaching full travel, possibly as little as 50% travel.
Solution: Remove token(s) & maintain air pressure.
Scenario 4: In order to get a decent amount of travel from your forks you’re running them so soft that you have used 30%+ of your travel just getting to sag point.
Solution: Remove token(s) & increase fork pressure.
** Removed? WTF? All I ever hear is people telling me to add more tokens!? Well tokens are a double edged sword, too few and you risk blowing through your travel or running your forks too hard, too many and you’ll never get full travel from your forks. Its worth considering both adding and removing tokens depending on what you want to achieve.
A quick note on ‘maintaining air pressure’. Above I list 3 air pressure options, drop, add or maintain. Maintain doesn’t mean literally keeping it exactly the same, but rather that the pressure you’re running is about right, and its the progression in the spring thats wrong. Changing the spring progression using tokens will effect the fork across the whole of its travel range, so some tweaking of the pressure might be needed to compensate, but its not the main factor at work here.

OK, I’m Sold. What do I Need?

There are four basic things you’ll need to make the magic happen.
  • A socket or good quality spanner to fit on the air top cap. A decent wide adjustable (30mm) spanner is fine for occasional use. It might fix something around the house too.
  • A token compatible fork as found on almost all the Bird bikes. See below for the RockShox compatible fork options.
  • Some tokens suitable for your forks. You probably received some with your forks or bike, but you can always buy some more here: http://www.bird.bike/?s=token&post_…
  • A good shock pump. Specifically one good shock pump. You may own more than one. When testing your set up, always us the same pump. Even the same pumps from the same brand can yield different results when using two pumps. Its always best to stick with a single pump as no-matter how inaccurate, its likely to be consistent, which is the main thing. Its not actually important whether it reads 100PSI but its actually 120PSI. What counts it that when you pump it to 100PSI its the same pressure as the last time you did that.

RockShox Token Compatible Forks and Base Settings

The following chart shows the travel options for each RockShox token compatible fork, and how many tokens you should expect to find under the top cap should you open it up.

How many tokens did your fork some with?

A Rough Guide to Get You Started

As I mentioned earlier, there are no hard and fast rules on the use of tokens. Every one is different and what suits you might not suit someone else. However, as a starting point, I would recommend for the average weight, average trail rider:
  • 32mm Chassis Forks (Revelations etc.) – As from the factory.
  • 35mm Pike Forks (RC & RCT3) : +1 token for every 20mm away from the max travel of the fork (160mm on a 27.5) + 2 tokens.
  • 35mm Yari and Lyrik Forks : +1 token for every 20mm away from the max travel of the fork (180mm on a 27.5) – 1 token.

Recommended tokens shown in blue.

So How Do I Do This Then?

OK, so you’re going to go for it! Good stuff. Here’s the guide from RockShox on how to do it, but don’t worry its not hard.

Keep In Touch!

Thanks for reading, if you want to hear more from us on other technical insights, don’t forget to like our FaceBook Page to get Tech Talk articles direct into your timeline each week (or as often as I can write them!). Any questions drop me comment into the comments area and I will answer them as quick as I can.
Ben