BOS Idylle Rare Air FCV Fork

The Ride

All the numbers and figures don’t mean much if the Idylle doesn’t ride well, and given that the RockShox Boxxer and the Fox 40 are both pretty solid options these days, the Idylle has its work cut out for it if it’s going to justify its price.


Running on 37mm stanchions, the Idylle falls between the Boxxer and the 40 in terms of size, and that about sums up where it lands in terms of stiffness, too: it’s stiffer than a Boxxer, but not as stiff as a 40. That applies to both fore-aft stiffness as well as torsional stiffness.

Notably, even though the Idylle isn’t the absolute stiffest fork out there, I never noticed the fork bind up under load. Particularly on the Boxxer, I’ve found that the fork’s action can become less smooth when hammering through deep holes, since the fork flexes and the bushings bind. The 40 is better about that issue, but that extra stiffness comes at a cost—it’s less forgiving, and can beat up my hands and forearms a bit more.

The Idylle strikes a good middle ground between these two: it’s definitely more comfortable after a day of riding than the 40, but it also didn’t have any of the stiction problems that are sometimes an issue on the Boxxer. Supposedly this is due to BOS’s insane attention to tolerances and perfectly honed internals and bushings; the dialed internals are apparently far less inclined to bind under load.

I can’t personally say whether their tolerances are actually that much different than other brands, but I can definitely say that the Idylle is incredibly smooth in all situations, and that there’s no bushing knock or play whatsoever.


After a brief break in period, it was time to assess how the fork did when the going got rough. Two things became apparent pretty quickly:

First, the Idylle has really, really good small bump sensitivity. Even when I was running pretty high pressure (210psi), the first ~60mm of the stroke is extremely supple and smooth. I can honestly say that this is very close to the level of suppleness that you get out of a coil sprung fork.

While current model Boxxers and 40’s are pretty good in this regard, the Idylle is better. I’m admittedly somewhat baffled that a fork that’s running such high pressures is still so smooth at the beginning of it’s stroke, but I suppose that’s another testament to the Idylle’s high quality seals and tight tolerances.

The second thing I noticed is that it’s quite progressive. The Idylle uses a hydraulic bump stop, which combined with the natural progression of the air spring, makes for a fork that’s fairly hard to bottom out.

I find that some forks are a bit too progressive (i.e., the ramp up comes too early, and I don’t use all of the travel except on absolutely massive hits), but more often for downhill forks, I find them to be a bit too linear. On my prior Boxxer World Cup, I had a hard time getting the air pressure at that magic number where it was supple over small bumps, but still retained mid-stroke support and bottom out control. While I haven’t spent as much time on one, I’ve found the Fox 40 Air to be better in this regard.

The Idylle, like the 40 Air, is very good on this front. Once I got the air pressure in the Idylle to where I liked it for mid-stroke support, I felt that the progression was about right. I’d get deep into the travel on fairly large hits, but only on huge hits would I notice the front end bottoming.

Noah Bodman reviews the BOS Idylle Rare Air FCV Fork for Blister Gear Review
Noah Bodman on the BOS Idylle Rare Air FCV Fork.

On a few large drops that had bombed out, brake-bumped landings, I did get a “clunk” on bottom out. But on a “normal” hard hit, the fork would ramp up significantly in the last ~30mm of travel, thus avoiding any harshness. And perhaps most impressively, as I noted above, I could add or remove a bit of pressure to fuss with the mid and late stroke firmness, but the suppleness at the beginning of the stroke remained really good.

I did investigate reducing the volume of the air chamber to make the fork even more progressive, not because I really wanted that, but mostly because I was curious about what was going on in the air spring. The air spring uses an internal tube within the stanchion that you can’t get into without tearing the fork apart. Given the lack of serviceability of the Idylle (more on that below), I didn’t go any further, but suffice it to say, it’s not as easy as simply adding something like a bottomless token.

NEXT:The Damper and the FCV System, Maintenance and Support , Etc.

10 comments on “BOS Idylle Rare Air FCV Fork”

  1. Interesting. Seems like BOS is in a chicken and egg situation. They need better service in NA to sell more forks, but they need to sell more forks in NA to justify funding better service options.

    I wonder if the FCV is closer to the Penske-developed Reaktiv valving in some of the newer Fox shocks on Trek bikes than it is to a Spec Brain? I’ve been on the Reaktiv stuff for over a year now, and it is significant. Super supple early travel, but still stays high in the travel, like you noted on the FCV system. Hoping Fox gets Reaktiv valving into a fork in the next year or so!

    • Agreed on the chicken and egg thing.

      I haven’t really played around with one of the Reaktiv shocks yet, but from what I’ve read, those valves are designed to open at higher shaft speeds (and thus higher oil pressures). It’s working towards achieving the same basic goal as the FCV, but it appears to be going about it a bit differently. The brain and the FCV are both inertia valves, meaning that they open when the valve is physically rattled open (as opposed to a speed sensitive damper that’s opened via oil pressure). But I think the similarities between the brain and the FCV end there – the actual execution seems to be a bit different.

  2. I feel like, BOS is missing out so much in terms of profit, among others by being so restrictive in the whole rebuild and DIY maintenance thing. I know a lot of people can afford BOS and would want to get a BOS fork, but the lack of parts, the lack of service centers, among others really kills it. I want one no doubt about it, but what a deal breaker that you’d have to send a fork for servicing to their headquarters or for any of there service centers, if any exist. I’m somewhere in Asia and I don’t know if they have a service center here.

    I do understand the do it yourself and your warranty is void thing. Still they should at least offer parts available for everyone and how to do maintenance themselves. I feel that it doesn’t affect warranty at all. After all, the customer already knows that if they touch the innards or do repairs or do maintenance themselves, they already know what they’re getting into.

    C’mon BOS! Want to love you but you’re pushing me away!

  3. Thank you for a great review. I’m running the BOS myself on an new bike so I have spend quite some time now setting up a decent set-up. I’m exactly same size and weight as you so I was very surprised about your settings and would be very pleased if you could clarify / confirm a few things: I run 195 psi so given you like a harder set-up 205-210 psi is probably okay, However, looking at the LSC, HSC, Rebound settings I’m counting like BOS. Meaning from fully closed and then anti-clock wise (I understand you count opposite?). So in BOS-terms I’m running this setup: LSC:12, HSC:18, Rebound 20-22. I’m trying to count where you are. My simple observation tells me something like LSC: 9, HSC:10, Rebound 16-17. Combined with the 210 psi it looks like a damn hard and slow setup compared with mine. Can you confirm or correct the numbers above? Finally, any chance you would test the Void? Could you some reference there as well…

    • Hey Martin,

      That’s correct – I’m counting clicks opposite from how BOS talks about them. I guess I’ve just always counted from fully open since that makes more sense to me; more clicks = more damping, whereas with the way BOS counts, more clicks = less damping. So counting them the BOS way, I’m running 9 clicks LSC, 4 clicks HSC, and 17 clicks Rebound.

      So yeah, I’ve got the compression circuits dialed in quite a bit stiffer / more supportive than BOS’s recommended settings, and my rebound is a smidge slower than what they recommend (which probably makes sense, given that I’m running higher air pressure – more air pressure means more force on the rebound circuit).

      And I’d love to test the Void. I just need to figure out how to get my hands on one!


  4. Thank you Noah. I give it a chance and try this stiffer setup. Sometimes you got to try something new. Again thank you for a great review.

  5. Great review!

    I know you have touched on this, but I’m looking for some reassurance. I just purchased a Rocky Mountain Maiden, that has come with the Idylle Air. Right out of the box the fork sounds horrible, like a suction or wheezing noise anytime it is compressed and released. I expected some noise, but not this amount.

    You say this stopped after some use?

    • Yup, that was exactly how mine sounded. It probably took ~10 minutes of bouncing around on it before it quieted down and started to feel good. It continued to get quieter and feel better for the first 2-3 rides. Since then, it’s been great.

  6. Thanks for this awesome review! I was simply searching around for what other riders thought of the BOS air. My Opinion and observations about how the fork functions and what its like to own one is parallel with yours Noah. I ve been on a jedi since 2013, 3 years with the 2013 frame on a 40 FIT and the last few months on a 2016 jedi first with a boxxer WC now with the BOS Air fcv. It was actually pretty nerve racking being presented with the opportunity to get on a BOS after canfield offered the upgrade as i have heard Nightmare stories about their customer service. in the end i sold the boxxer and made up the difference to upgrade to the BOS. An upgrade it truly is.

  7. One advantage of not providing user friendly tool-free knobs is reducing chances to get pranked by friends :)
    It also gives opportunity to aftermarket solutions. Will try 3D printing a tool (depending on how stiff the flat screws turn).
    I accidentally found someone offering blow-off screws with integrated buttons :)

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