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BOS Void DH Air Shock

by BOS on 2nd March 2012

Bos is a name synonymous with suspension performance and associated with one of the most successful and fastest riders out there. Something that's not often synonymous is air and DH shocks. Read the Bos press release to find out if they have cracked it with the new Void shock.
I was no longer a secret : everybody knew that Bos was working on a DH air shock since several months.

BosĎs research was actually oriented in a very precise way. The VipíR 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 the company, as it had always upheld the coil spring for DH... so far.

Nevertheless, Bos has already produced air shock. VipíR 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 couldnít
launch an air shock without reaching the same working than a coil shock. Which is now the case.

The main interest of an air shock is obviously the weight.

The gap between Stoy RaRe with spring and Void reaches 356g!

But an air spring also provides other advantages :
You donít need any more to wonder about what spring rate you will have to elect depending on your weight. Itís 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 VipíR, itís fast and easy to set up the volume on Void, and it doesnít 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 canít 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 itís also noticeable on the very first millimeters, 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
Pneumatic settings
Pressure (spring rate)
Volume (progressiveness)
Needle bearing mounting kit
weight : 519 g (240 mm) without mounting kit


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