Trek's 2018 Mountain Bikes Feature Shocks Unlike Anything You've Seen Before 11

All your questions answered about Trek's unique Thru Shaft shock technology.

Trek's 2018 Mountain Bikes Feature Shocks Unlike Anything You've Seen Before

As history shows, Trek Bikes isn't afraid to try something new in the suspension realm. Today they've released thru shaft shocks, one of their wildest creations yet. They'll come equipped on several high-end Fuel EX, Remedy, and Slash models in 2018.

Trek claims that traditional shocks with an internal floating piston (IFP), which compensates for the change in damper volume and displacement, don't respond quickly enough due to lag in the system. You can see the lag illustrated in this (exaggerated) animation:

The new Thru Shaft design eliminates the IFP by allowing displacement outside of the shock. According to Trek, this provides a faster response, constant connection to terrain, more traction, and ultimately more control:

Currently thru shaft suspension is used in Indy, Lemans, F1, short track, and MotoGP racing. Trek provided the following Q&A to help explain exactly what's going on and why they think it's a benefit for riders.

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. 

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. 

R-Dog and Casey Brown let it rip on the new Remedy with Thru Shaft shocks.

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. 

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. 

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.

Lust worthy. The 2018 Trek Remedy 9.8 features a 230x57.5mm RockShox Deluxe RT3 shock with RE:aktiv and Thru Shaft 3-position damper.

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.

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 2018 bikes feature the new shock? 

The 2018 Trek Slash 9.8, complete with a 230x57.5mm RockShox Deluxe RT3 with RE:aktiv and Thru Shaft 3-position damper.

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. 

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.

Trek's 2018 Fuel EX 9.9 29 joins the party as well, sporting a 210x52.5mm FOX Factory Float EVOL shock with RE:aktiv, Kashima Coat, and Thru Shaft 3-position damper.

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.


Learn more at Photos by Sterling Lorence and Ian Collins.

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  • MrBlackmores

    7/14/2017 1:12 PM

    My opinion about this shock:

    PD: sorry for Google translator

  • prancisfena

    7/13/2017 7:17 PM

    Would a normal rider really feel that "lag"?

  • Serge-W

    7/12/2017 1:14 PM

    Nice one, but not exaclty a new concept.

    My '94 AMP B3 had a thru-shaft shock. The shock itself was super-basic, but that was only possible because it was thru-shaft. The simplicity allowed Leitner to CNC some simple shock-parts and bolt them together as oil-filled tube, a thrushaft and a piston with a hole in it.

    I guess not much R&D went into those, because performance-wise, there was nothing to write home about. But the concept of less hysteresis always made sense. Would be keen to try out, what the new thru-shafts can do.

  • WaffleStomp

    7/12/2017 10:21 AM

    Sooo... maybe I'm misunderstanding this, but it looks like this is just an effort to eliminate the IFP from a monotube shock using some overkill engineering.

    What exactly is the problem with twin tube shocks then? No more IFP, no reason it shouldn't do the same thing as this.

  • frazzle

    7/12/2017 12:53 PM

    Both Mono tube and Twin tube shocks have to have an IFP to compensate for the oil displaced by the shaft as it compresses.The difference between them is the way the oil flows through the damping circuits.

  • WaffleStomp

    7/12/2017 1:58 PM

    Some like Cane Creek do, but in the reserve tube where it doesn't matter much. But others like DVO and (I think) Ohlins use bladders instead. Also, twin vs mono tube should only be referring to the storage of excess oil, monotube uses the IFP and nitrogen charge, twin tube uses a primary and reserve tube. The damping circuit on the piston should not be affected by the oil reserve design, no?

  • frazzle

    7/12/2017 2:48 PM

    I misunderstood what your meaning by twin tube. I was thinking of cane creek DB and Fox X2 as they call themselves a twin tube design aswell. But that is very different to what the automotive industry call a twin tube. The problem I could see with an automotive style twin tube in an mtb would be that it always has to be orientated vertically and the oil in the reserve tube could be prone to mixing with air over rough ground. Marzocchi have used this design in there forks before.
    It seems a bladder design would be just as good as a thru shaft to me, or even better as you can keep the oil pressurised to limit cavitation.

  • Vertti83

    7/14/2017 4:02 AM

    I was thinking also the bladder thing, that isn't DVO using such in their Topaz(?) shocks to eliminate the friction from IFP seals..?

    Another curiosity is that will these thru shaft shocks be more prone to cavitation as the oil isn't pressurized..?

  • Condro

    7/12/2017 8:46 AM

    Pretty inventive!

  • Triber66

    7/12/2017 8:19 AM

    Ughhh...... to stay current, I don't know whether to get Transitions SBG or Trek's through shaft shocks....

  • ryan_daugherty

    7/12/2017 9:18 AM

    buy neither and just get an Ellsworth. Everyone will know that you give zero shits about the latest MTB trends then.

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