Air Sprung Bos Idylle RaRe | Fresh Produce

Hot on the heels of their Void DH air shock comes this new air sprung version of the Idylle RaRe fork. It’s a big move for the French company, so we thought it deserved an exclusive video interview…

And who better to talk to about the development of both this new air fork and the Void rear shock than the very man who designed them: Arnaud Jacob. And please excuse any sound or video issues, it’s the best we could manage using Skype, but hopefully you’ll find it interesting.

Update: It seems that some people were having major sound/video syncing issues with this interview, but we’ve hopefully now sorted this. (And yes we know it’s still not perfect, but it’s a hell of a lot better)

So, some seriously big talk from Bos there. I mean it really does seem like they believe that the days of seeing coil springs from Bos are numbered, even at World Cup DH level. Many people have said that air will never replace a coil spring for downhill use, and maybe it still won’t altogether, but Bos aren’t a company that are led by any kind of fashion, everything they do is for a performance reason, and if there was one company that we thought we might never see an air DH product from it was Bos. They’ve always made it clear that they would never produce a product that sacrificed performance for a lower weight, but it seems like 2012 is the year when they’ve finally managed to equal, if not surpass the performance of their coil sprung products. Exciting times indeed if they have pulled it off. We’ll have a full test on these in a future issue of the magazine (as I write this Steve Jones is currently galavanting around Europe testing them out), but in the mean time it’s worth noting that Bos team riders have all chosen to run these air forks this season despite being able to run the coil version if they want to.

Enough chat though, here’s the fork in all its glory, and the distinctly ‘frenglish’ press release from Bos…

Classic Bos style, but note the new cut-out arch on the lower legs.

The view from the top, and the air valve which we thought we might never see on a Bos DH fork. On the right hand side you get your rebound adjuster and an air bleed screw which simply needs unscrewing after every five hours of riding.

At the bottom you’ll find both the low and high speed compression adjusters.

Even just the dropouts are a class act. The long washer means the lower legs are protected from any damage caused by tightening up the bolts, and if you get a bit carried away tightening them and strip the threads then you can easily replace that part.

The hose guide: simple, neat, and effective, just the way we like things.

What excess material?

They even look just as good from the back. Note the hollowed out arch and the way Bos have machined the upper parts of the stanchions to help keep the weight as low as possible.

Here’s that Frenglish press release…

In the opening round of the DH world cup in Pietermartzburg, the observers could notice that the Bos pro riders used a special prototype of Idylle RaRe, featuring an air spring. Since those riders made very positive and unanimous comments about that fork – as well as other test riders – Bos decided to launch it earlier than what was previously planned. The new Idylle RaRe immediately and definitely replaces the “old” one. It’s already available and, coming after the Void, released a few weeks ago, it completes the full air suspension set intended for DH racing by Bos mtb.
Full air set intended for DH

The Void showed the way. Idylle RaRe follows a few weeks later, by adopting also an air spring. That’s a big move made by Bos. It may seem surprising that the french company goes so suddenly into air springs. But this choice is clearly motivated by Bos’s philosophy, whom credo is always the seek of performance and efficiency. RaRe isn’t just a marketing name at Bos : RaRe models are 100% identical to the forks and shocks used by the official riders. And they lust be available for amateur racers as quick as possible.

In 2012, Bos is making its come back to world cup racing, with the Labyrinth Team (Rémi Thirion and Sabrina Jonnier) but also Julien Camellini and Pierre Charles Georges. All these riders could test the RaRe “air” prototype. And all decided to ride it. Facing this situation, Bos decided to speed up, and launch with no delay the new RaRe on the market.

An even more performing fork

As for the Void, Bos’s aim consisted in reaching a spring curve similar to the one of a coil spring, with the air system. A loss of weight was also – obviously – a target. But as always at Bos it could not be reached if the cost was to decrease the performance. The result is that the air spring not only features a way of working similar to a coil one, but the fork itself according to the riders who tested it – is clearly more sensitive on the first inches of travel.

No preload effect

Therefore, the air spring of the RaRe features a very linear curve, with almost no rate increase at full travel. Incidentally the riders preferred to keep the hydraulic bump stop featured by the fork, instead of using the air spring to handle the bump stop function (as for the Void). Bos respected and followed that choice, which shows clearly the way of thinking of the company. By removing the hydraulic bump stop, we would have saved a few grams more. But efficiency remains the priority…

Another characteristic of the Bos air spring us the lack of “preload effect” while getting to full compression. Usually, air systems suffer from this effect. But the Bos one, with its auto balanced chambers avoids it. Even with a high pressure in the air cartridge, the fork keeps very sensitive. So, here is a fork, featuring all what classically makes a RaRe : machined stanchions, titanium bolts, hydraulic bumpstop, high performing open bath cartridge, with three ways of hydraulic adjustments… But
an even more performing RaRe! We are not saying this, but the riders. Ask Julien Camellini…

Weight decreases, price stays the same

You are certainly impatient to know if the weight loss is significant… It’s actually 300g less. Nevertheless, the retail price stays the same at 1990 euros.

RaRe means Race Ready
That’s the reason why RaRe is written as a single word, but with two capital “R”. Don’t forget it !

Hydraulic fork featuring…
Open bath cartridge
Air spring
Travel : 200mm
Damping adjustment: Hi speed compression, Low speed compression, Rebound
Hydraulic bump stop
Air bleeding screw on top of the right stanchion
Stanchions : aluminum 7050 – ø 36mm, machined between the crowns
Lower legs : magnesium
Triple crown : alu 6061 forged + machined.
Steerer : 1”1/8
Axle ø 20 mm.
Postmount IS
Weigth : 2850 g

And finally for those of you who missed the Void rear shock in the magazine a few issues back, here’s a picture of it, and once again a press release with some interesting English…

As with the fork you get a rebound adjuster (the black knob) alongside low and high speed compression adjusters (the screw and nut at the other end). The unique ability to rotate the air valve around the shock body means that even if your shock is located in some hard to reach part of your frame you should still be able put the valve somewhere where you can get at it.

Here’s the press release…

It was no longer a secret : everybody knew that Bos was working on a DH air shock since several months. Bos ‘s research was actually oriented in a very precise way. The Vip’R has been the first visible result of that research. But bringing the air spring to DH was another challenge. It seems that it has been achieved, since the Void, after having been testing for weeks, has been declared fit for service, and will be available very soon.

The first ever DH air shock produced by Bos

Void is the first DH air shock produced by Bos. I may seem surprising for those who know well thecompany, as it had always upheld the coil spring for DH… so far. Nevertheless, Bos has already produced air shock. Vip’R is not the first. 10 years ago, Bos made a cross country shock for a big bicycle brand. And if Bos stayed focused on coil sprig for DH until now, it never made it a matter of principle. Bos always said that when an air spring would reach the same level of performance and reliability than a coil one, then, there would be no reason to avoid producing it. So, we can guess this is now the case !

Goal : to reproduce the working of a coil spring

The main problem that engineers faced was that an air spring is progressive : its rate increases while it is compressed. On the contrary a coil spring features a constant rate. If you want to use all the travel and have an efficient control of the shock through damping, this constant rate is a key point. Therefore, Bos couldn’t launch an air shock without reaching the same working than a coil shock. Which is now the case.

Le main interest of an air shock is obviously the weight. The gap between Stoy RaRe with spring and Void reaches 356 g !

But an air spring also provides other advantages : You don’t need any more to wonder about what spring rate you will have to elect depending on your weight. It’s a big step, especially with Bos shocks, which feature very precise damping, and therefore need the same level of precision for the springs, with steps of 25 lbs / inch.

An air bump stop

We already explained that the air spring from Bos featured a rate curve similar to a coil. Nevertheless, when you reach the last millimeters of strike, the rate raises. Which explains why there is no hydraulic bump stop in the Void, and neither rubber on the rod. That way, the air spring also acts as a true pneumatic bump stop. But with a huge difference compared to the rubber item. With a coil spring the rate increases suddenly when the rubber is compressed. With the air spring, the rate rises smoothly. Moreover, this rate progressiveness is adjustable, through the volume of the air chamber. As same as with Vip’R, it’s fast and easy to set up the volume on Void, and it doesn’t require any tool.

Five ways of setting

Consequently, we can say that Void features five ways of setting : three hydraulic and two pneumatic, as the spring rate and progressiveness can be adjusted, when a coil spring can be… replaced. By the way, we insist on the fact that the pressure in the reservoir is not adjustable and can’t be considered as a way of setting.

While testing Void on the track Bos could notice that the air spring showed more sensitive than the coil spring. We mentioned it already about the last millimeters of travel, but it’s also noticeable on the very first millimetres, with a lower starting point. Combined with the high tolerance assembly of Bos which reduces friction, the damping suffers even less from mechanical interferences, then controls better the behavior of the shock.

Stoy RaRe was considered as a reference in terms of function and performance. Void goes one step ahead.

Void in short

Void is very similar to Stoy RaRe. Both share the same main specs :

Specific setting for the bike
Three ways of hydraulic settings
Aluminum rod
Needle bearing mounting kit

The main difference is the spring, and consequently the absence of hydraulic bump stop! The diameter of the air chamber is the same than the diameter of a coil spring, which allows to mount the shock on any bike. The valve can be oriented frontwards or backwards, without any tool. It can also rotate around the air chamber (the only fordidden place is in front of the reservoir). That way, Void is highly compatible with any bike.


Piggy back hydraulic shock
Air spring
Available length x stroke : 222 x 68 / 240 x75 / 267 x 89
Internal valving specific for each bike
Hydraulic settings : High speed compression, Low speed compression, Rebound
Pneumatic settings: Pressure (spring rate), Volume (progressiveness)
Needle bearing mounting kit
weight : 519 g (240 mm) without mounting kit.


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