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Discussion Starter · #1 ·
Thought there might be some interested people in this. Today I modified the reactiv shock in my 2018 from 210x52.5mm to 210x55mm.

I have heard already people putting 210x55mm shock in their fuel ex's to give them more travel, but this size shock is hard to come by here in NZ unless I'm paying RRP for a new one.

Modifying the shock was easy to do, this is what you need to do if your interested.

1. Remove shock from bike and remove all air.
2. Unscrew air sleeve assembly from eyelet assembly
3. There is no volume spacer in this shock but a small 2.5mm alloy ring. This is at the top of the shaft
4. I cut this off carefully with side cutters.
5. Reassemble everything.

See pictures below


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Well done! I've seen people remove these spaces on Yetis and a few other brands but not the Fuel yet to date. Cool stuff.

It's like removing the pin in DRCV to run extra volume all the time and improve that lack of mid stroke support. Love it.
 

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Discussion Starter · #4 ·
Unfortunately I haven't been for a proper ride yet, just up and down the road. I will hope get out in the next couple days.

I actually picked up a 2nd hand shock someone removed from their fuel ex for $50. I modded that one as described, as I wasnt completely 100% on what I was doing. I figured it was a small price to pay if it didn't work.

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I did this mod a while back and you won't notice any difference unless you were bottoming out the shock before. It gives you an extra 6-7mm of travel before bottoming but doesn't change anything else.

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Discussion Starter · #6 ·
Just taken my bike for a decent ride since the mod which included plenty of ups and downs.
I'm running a slightly lower pressure in the shock now I have more stroke length.
The rear feels plusher due to the lower air pressure and I noted I did bottom out a few times in the downs. The bike is feeling a bit more capable on the downs and the same as it was previously on the ups.
I feel it might be the reactiv tune that might be holding the bike back now on the downs but it does allow the bike to pedal better on the flats and ups.
I would say the bike is marginally better than what it was before the change but worth it for me to do.

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Discussion Starter · #8 ·
FWIW: Reaktiv doesn't function in Open mode. It is switched in in Medium mode.
Interesting, I thought reactiv would have affected the entire shock, as it's a shock tune.
I know on my Top Fuel open mode doesn't feel like open mode on any other XC bike rear shock I've owned in the past.

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You can feel it pretty easily with the shock off the bike by compressing it by hand with the air can off or at zero pressure. In Open, you can compress it (working against the IFP pressure or that plus air in the can if it's still on) and it'll feel like any other shock. In Medium, it gets very hard to compress if you can compress it at all until you overcome the Reaktiv valve.

The Reactiv valve works like a lockout until it's overcome, at which point it blows off and flows through the medium circuit as if it's not there.

While it can be easily felt by hand with the shock off the bike, it's pretty subtle in effect when riding.
 

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Discussion Starter · #10 ·
So would you be saying that the reactiv tune on a Trek Top fuel shock is pointless as the shock can only be locked or in open modes?

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It's my understanding that RE:activ is integral to the damping system in general, as it is a regressive damper.
per Trek:
"RE:aktiv can function effectively in all three settings, allowing you to simply pick the proper setting and let her rip. Wouldn’t it be nice to no longer interrupt your flow to flip between suspension settings during a ride? It simply makes the shock better all the time."

Maybe [email protected] can clarify this.
 

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Claims and reality might differ slightly. I was working on two '16 Reaktiv shocks a week ago and the effect was very clear on both as I described above, a very distinct effect in Medium and none in Open. On the non Reaktive version you can easily discern by hand the increase in low speed damping between Open and Medium, but without the Reaktiv effect. My understanding is that there is a spring that presses against the blow off valve and the tension goes from basically nothing in Open, to a lot in Firm as you rotate the blue lever. The rule has been that if you want the benefit of Reaktiv, ride in Medium. It may be that they've more recently changed the spring and preload to make it more effective in Open.

I'll add that in some shocks you could hear clicking/clunking in Open mode as the spring had basically no preload and play so that the Reaktiv valve was freely moving back and forth making noise (and of course being non-functional as far as Reaktiv was concerned). If you sent the shock back to Fox complaining about this, they'd adjust or shim it to remove the play so that it was no longer noisy.
 

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Discussion Starter · #14 ·
Claims and reality might differ slightly. I was working on two '16 Reaktiv shocks a week ago and the effect was very clear on both as I described above, a very distinct effect in Medium and none in Open. On the non Reaktive version you can easily discern by hand the increase in low speed damping between Open and Medium, but without the Reaktiv effect. My understanding is that there is a spring that presses against the blow off valve and the tension goes from basically nothing in Open, to a lot in Firm as you rotate the blue lever. The rule has been that if you want the benefit of Reaktiv, ride in Medium. It may be that they've more recently changed the spring and preload to make it more effective in Open.

I'll add that in some shocks you could hear clicking/clunking in Open mode as the spring had basically no preload and play so that the Reaktiv valve was freely moving back and forth making noise (and of course being non-functional as far as Reaktiv was concerned). If you sent the shock back to Fox complaining about this, they'd adjust or shim it to remove the play so that it was no longer noisy.
What about reactiv shocks that have no medium and only have an open or locked out, how does the reactiv work on them?

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Discussion Starter · #16 ·
^^^ AFAIK, you only get Reaktiv on higher end models, like the FEX8 and above. 7 and below, whether three or two position shocks, don't have it.
My 2018 Top Fuel 9.7 has a reactiv rear shock with remote, only 2 modes - open and locked. All 2016 - 2018 Top fuels had this shock setup

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My 2018 Top Fuel 9.7 has a reactiv rear shock with remote, only 2 modes - open and locked. All 2016 - 2018 Top fuels had this shock setup
Right, but with that you get the Reaktiv version of "locked out" which is quite a bit less firm than the classic, brick-like DPS lockout.

Boils down to personal preference, really. When I was racing 100s seriously, I kind of felt like I needed that super-firm DPS lockout, because every 100 has some climby road sections. For trail riding, the Reaktiv lockout is more useful. To me, anyway.
 

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I have not worked with 2 position Reaktiv shocks so don't know how they're set up. As I mentioned, it's a blow-off valve with variable preload based on how it's set up and the position of the blue lever. Trek/mfgr decides when and how much it comes into play in the different lever positions. If you're curious about your specific shock, you could pull it off the bike, let all air out (better to remove the can) and see how it behaves compressing it by hand. If Reaktiv is functioning in the Open position, you'll feel a great deal of resistance compressing it, much more than what you'd feel due to IFP pressure alone.
 

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Discussion Starter · #19 ·
Just did this now on my spare reactiv shock. I couldn't compress at all by hand in open mode. But leant on the shock against a table with my weight against it and I could compress it in both open and medium modes. It was slightly slower to compress in medium mode. I couldn't compress in firm mode. Tbh I couldn't really find any difference between compressing in open and medium apart from the speed.

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I have to let every last fraction of a psi out of the air can, or better, remove the air can to be able to compress it easily enough to feel the damper and Reaktiv effect.
 
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