Flow MTB Air Fork Upgrade

Compatibility

TruTune inserts come in specified equivalent number of tokens. Do not exceed the manufacturer specified maximum number of tokens / spacers for your fork model. You can check your Fox fork here and your RockShox fork here.

Fox 36 / 38

Standard: 5 (equivalent token length), Short: 4 (equivalent token length)

• Fox 36 FLOAT NA2 2018+ (ORANGE spacers)
• Fox 38 FLOAT (YELLOW spacers)

Not compatible with Fox 36 Rhythm FLOAT NA 2 (PURPLE tokens) - our Fox 34 model should be used.

RockShox 35/38mm

Standard: 3 (equivalent token length)

• 35mm and 38mm Rockshox DebonAir(+) (ZEB, Pike, Lyrik, Yari)

Equivalent to GREY / RED bottomless tokens. Not compatible with Dual Position Air springs.

Heavy rider (90+kg) or on E-bike? Choose our Short model where available.

Installation

WARNING: modifying any aspect of your suspension without the appropriate training and experience can result in serious injury or even death. Installation should be carried out by a competent technician. We cannot be held responsible for the results of incorrect installation of our product and assembly of your suspension.

The following are guidelines for installing Trutune plug and play inserts for mountain bike front air suspensions. Please refer to the fork manufacturer manual for up to date instructions on assembly / disassembly for your specific model.

1. Firstly, secure the bike in a suitable stand to ensure the bike is safe to work on. If the forks are separate from your bike, use a suitable vice or the clamp from a bike stand with soft jaws to avoid damage to the forks or bike.
2. Unscrew the dirt cover to expose the valve and put the cover in a safe place.
3. Using a small tool (Allen key) remove ALL the pressure by gently pressing the valve.
4. Using an appropriate socket or cassette tool (depending on year/model) remove the top cap, gently applying pressure to ensure the tool does not slip.
5. Once the top cap is removed, remove ALL plastic volume spacer tokens. OEM tokens can be used in conjunction with a TRUTUNE insert, however it is important that the number of tokens plus the token length of the TRUTUNE insert does not exceed the manufacturer specified maximum number of tokens for the fork.
6. Securely attach the insert to the top cap (for RockShox forks, this will generally be a screw thread, for Fox forks a snap fit).
7. Apply a small amount of grease to the cap o-ring and then Install the top cap with the TRUTUNE insert into the air chamber and tighten to the manufacturer recommended torque using a torque wrench
8. Using your air pump, pressurise the positive air chamber to your desired pressure, or alternatively consult the manufacturer pressure charts for your fork model and weight. Allow 30 seconds for the pressure to settle, as it will drop slightly after charging, and top up to the right value, ensuring to pump the fork a few times to equilibrate both chambers. With a TRUTUNE insert installed, we recommend to increase pressure by 5% above preference / manufacturer recommendation as a starting point. 
9. With the aid of the floating o-ring on the fork (if available), ensure the ride sag position is within the manufacturer specification (or personal preference). If not, increase or decrease pressure as appropriate.  
10. Finally, replace the dirt cover onto the top cap valve carefully to finger tight.

Setup Guide

Click here for SET UP advice

FAQ

HOW CAN ACTIVATED CARBON POSSIBLY INCREASE THE EFFECTIVE AIR VOLUME?

It may seem counterintuitive, but adsorption is how this happens. As the fork or shock is compressed, some air adheres to the surface of the carbon. The air adhered to the carbon can have much higher density, and so reduces the pressure in the rest of the gas (compared to a chamber without any activated carbon). You can find out more on our Technology page.

IS IT THE SAME AS REMOVING TOKENS?

Having activated carbon in your fork is not the same as just removing tokens. In addition to the main physical effect - adsorption - which reduces pressure build up, there is heat exchange between the air and carbon. Usually an air spring is softer at slower speeds than fast speeds, which is not desirable, as high speed movements are associated with chatter, and low speed movements with how much support there is. Increasing the air volume requires higher pressure to get the right support, but the dynamic stiffness can become too high in the process. The heat exchange between air and carbon reduces the high speed air stiffness compared to an equivalent volume setup. In practice it means a much higher charge pressure can be used before the initial stiffness of the fork becomes unacceptable, allowing greater support and better small bump absorption than just running fewer tokens.

HOW LONG DOES THE INSERT LAST?

So far, our inserts have individually spent 100+ riding hours in forks without any noticeable changes to performance. Our earliest prototypes have been in forks for over a year and have maintained their adsorptive properties over time. We are continuing to test and monitor their durability and as we learn more about the long term lifespan we will make more information available.

IS THE ACTIVATED CARBON AFFECTED BY MOISTURE?

The effect is influenced by moisture, as water vapour competes with air in attaching itself to the carbon surface. In the sealed fork chamber, the amount of moisture is not sufficient to influence the effect or degrade performance over time. Provided the inserts are stored in dry conditions when out of the fork the performance will not be affected. Even after exposure to high humidity, the difference in performance is small as the surface area available for the air molecules at high pressure is still very high.

DOES THE CARBON RELEASE POWDER OR DUST INTO THE FORK?

We use a fine filter that we have selected out of many, having subjected it to shakers, test riding and dyno testing to ensure that there was no build-up of powder over time. We also apply a coating to the carbon to minimise powder production and allow a tight pack of granules in our inserts, reducing internal movement.

IS THE EFFECT DEPENDENT ON TEMPERATURE AND PRESSURE?

The effective increase in volume is temperature dependent, with around 5-10% variation between 0 and 40C. This is a small difference In terms of total fork volume, and so does not cause a dramatic change in feeling. The air pressure in the fork is slightly more sensitive to temperature than a regular air spring - the reason for this is that the carbon stores air in its pores which can be released by heating (and vice-versa trapped by cooling). The net effect in the fork depends on the amount of material, so we have found the right balance based on our test riding. The effect is also dependent on charge pressure, with higher pressure resulting in a smaller (but still stiffness reducing) effect. The pressures at which the activated carbon is no longer effective are much higher than those found in MTB air suspensions, including shock absorbers.

IS THE ACTIVATED CARBON AFFECTED BY SUSPENSION OIL AND GREASE?

When activated carbon is used in filters, substances accumulate and saturate the carbon as contaminated air or water flows through, and so over time the filters become less effective and need to be replaced. In the sealed environment of the fork, the only contaminants that can affect the behaviour are suspension oil and grease, and they do not continuously flow through the material and the degradation in performance is much lower.

Based on our lab tests, the inserts stop adding effective volume when they are half full of suspension oil (by volume), which for most of our products would be around 20ml. Typically, the total amount of oil inside the air chamber for a service is much less, around 3ml. In practice, most suspension oil makes its way to the negative chamber through the equalisation valve. There is also clearance around the sides of the insert, and away from the piston, which combined with our choice of filter help to avoid any oil or grease from coming into contact with the carbon in the first place. We do however recommend not using excessive oil or grease in order to minimise any performance changes over time.

Delivery

For spare parts, if they are in stock we will send them out the same day if we receive the order before midday (except weekends). If we receive the order after midday, we will do our best to despatch them same day, but it may be the following working day. Orders placed after 3pm on Friday will be despatched on the following Monday. We normally send spare parts by Royal Mail post (see below or our 'Shipping' page for cost/delivery times).

Forks, shocks and large/heavy orders go by courier. UK deliveries are with DPD Local, for overseas customers it's DPD, FedEx or DHL.  In all cases these are fully tracked services and you'll need to sign for the delivery - please provide a suitable address with extra instructions if necessary.

Returns

Customer Reviews

STAFF REVIEW 2nd April 2024

LanceStewart said...

"I had had been looking into this for a while, but like others I wasn’t sure if this £120 small black cylinder would be all that good. After seeing TFTuned were now stocking them I reached out and asked them, are these any good? The issue I had with my 2023 Zeb Ultimates was I couldn’t get them feeling less harsh out dropping the air pressure, but doing that, even with 3 tokens, I lost any mid stroke or bottom out support I needed. Installing the TruTune was easy and I included 1 air token as I ride an ebike and I also weigh a bit, added 10% PSI and a couple of clicks of LSC. My first ride I noticed the difference instantly, the fork felt more supportive yet more supple and on bigger days out I add a couple of clicks of HSC and that's it. Thanks again TFTuned!"

Staff response...
"NIce review Lance ... magic innit!!! Ruth @TFT"