Reaktiv 1

Trek Announces the New RE:aktiv Thru Shock

Building on their past history of incorporating suspension tech from F1 and auto racing, Trek Bikes have launched a new iteration of their RE:aktiv shocks. By dropping the internal floating piston found in most other shock designs and using a suspension concept currently found on Moto GP bikes, Trek claims that their new Re:aktiv Thru Shaft shocks are more responsive. 

How the RE:aktiv Thru Shaft Shock Works:

How does RE:aktiv with Thru Shaft compare to other all-mountain or enduro shocks like the Fox X2 or RockShox Super Deluxe? 

RE:aktiv with Thru Shaft is the only damper that eliminates oil displacement, the dynamic internal floating piston (IFP), and gas charge; as a result of this elimination, RE:aktiv with Thru Shaft has reduced hysteresis (lag) and more balanced damper pressures, which allows it to more quickly and effectively react to changing terrain. Overall, it’s a much more responsive damper with the same air spring performance.

internal view

A cutaway view of the RE:aktiv Thru Shaft Shock

Traditional Shock:

What does all of that mean? How does eliminating oil displacement benefit the rider?

In a traditional air shock, the damper shaft displaces oil as the shock moves through its stroke. The IFP, a gas-charged piston in the damper, compensates for this constant change in damper volume. As the damper rod displaces oil, the increased damper volume creates enough pressure to compress the gas charge and move the IFP. As the shock rebounds and pressure is reduced, the IFP will start floating back to its original position, and the cycle continues.

RE:aktiv Thru Shaft Shock


Is this technology proprietary to Trek?

Trek has an exclusivity agreement with both RockShox and FOX Racing Shox for two years. There are no patents on Thru Shaft, so after two years, other brands and FOX or RockShox could implement parts of the design. However, Penske still owns the patent for the RE:aktiv valve, so only Trek will benefit from RE:aktiv’s regressive damping.


The rod pressure from the gas charge and the stick and slip effect of the IFP’s movement create hysteresis, or lag, which keeps the shock from working as quickly as possible.

By eliminating oil displacement, we also eliminate the need for a dynamic IFP. With no dynamic IFP, hysteresis is dramatically reduced, which creates a damper that reacts to changing terrain significantly faster than anything else available.

Slash Action

How does RE:aktiv with Thru Shaft eliminate oil displacement?

Rather than a single damper shaft that displaces oil as it moves deeper into the stroke, Thru Shaft uses a shaft on either side of the damper valve that moves through a single, solid column of oil. As the main shaft enters the damper, the secondary shaft exits the damper on the other side. Conversely, as the main shaft exits the damper, the secondary shaft enters the damper on the other side. This results in a constant damper volume with no displacement and more balanced internal pressure.

How does all this affect the rider?

It’s a more responsive shock. With no IFP force acting against the damper shaft, small-bump sensitivity is greatly improved. Eliminating the dynamic IFP also eliminates its friction and stick and slip effect, so not only is the shock movement easier to initiate, it also changes direction much faster. The solid column of oil and immediate pressure balance result in more support and efficiency with faster response to terrain throughout the stroke. In total, this shock amplifies the responsiveness of a standard RE:aktiv shock, and keeps your rear tire glued to the trail so you can ride with even more confidence.


With no dynamic IFP, how does the shock manage heat-induced fluid expansion?

The longer-stroke RockShox version uses an external reservoir for thermal compensation.

Since the shorter-stroke Fox version has less total oil volume, Fox was able to include a thermal compensator within the main damper shaft.

Due to the use of a flow control check valve, thermal compensation on RE:aktiv with Thru Shaft takes place during moments when the shock is static. This eliminates the need for a dynamic IFP function and an associated IFP gas charge, which is necessary for traditional dynamic IFP shock function.

Slash Action

Do the added seals cause extra stiction?

Eliminating the dynamic IFP’s stick and slip effect and the IFP’s gas charge nose force on the main damper shaft greatly outweighs any potential added stiction from the additional Thru Shaft secondary shaft seals.

Which bikes feature the new shock?

Slash 9.8 and Slash 9.7; Remedy 9.8 and Remedy 9.8 Women’s; and Fuel EX 9.9.

Carbon framesets of the above platforms will also include shocks featuring RE:aktiv with Thru Shaft.

Why is RE:aktiv with Thru Shaft only available on the highest-end bike models? Will it make its way onto other models?

Initially, we are only offering RE:aktiv with Thru Shaft on the highest-end models because of development and production costs. We expect to offer it on more models in the future.


Can riders upgrade other Trek mountain bikes with this new shock?

No, we are not offering the new RE:aktiv with Thru Shaft shocks as an aftermarket upgrade at this time.

Is Thru Shaft something that we could see on DH or XC bikes?

We’re currently focused on using RE:aktiv with Thru Shaft in trail bike applications, as that is where we see the greatest performance benefits. However, as with any other new technology, we’re always exploring other potential applications.

EWS Slash Action

Is there a weight limit on RE:aktiv with Thru Shaft?

Since weight limitations are based on the air spring, and not the damper, the weight limits are the same as with the standard offerings from either manufacturer.

Is the setup process the same as traditional air shocks?

Yes. Riders will still set air pressure based on desired sag, and adjust the rebound damping accordingly. 

Can riders adjust the air spring volume?

Yes. As with other modern air shocks, riders can add volume spacers to both Fox and RockShox Thru Shaft shocks for a more progressive spring rate.

Is the new Thru Shaft shock user serviceable?

Yes. Recommended maintenance for Thru Shaft shocks is similar to traditional IFP shocks. 

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Okay so I see that the marketing wank is strong with this one.... look at that "traditional shock" video and tell me what you see wrong with it.... nothing... hmmm... what was that? something but you can't put your finger on it? I'll tell you what is a lie with that one: oil is a liquid is it not? which liquids do you know of that compress?? NONE! That video clearly shows a liquid compressing.... marketing bullshit to the highest degree right there.



The animation is correct.  Air is being compressed to account for the increased damper shaft volume as the shock compresses.  This is how an IFP works...



Watch it again Neanderthal.



It's maybe not the clearest animation ever, but if you have any basic understanding of how a shock works, you'll know that oil is passing through shims / ports etc in the damping element at the end of the shaft. Oil isn't being compressed, it's just being moved from one side of the damper to the other!


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