On our quest to demystify rear shocks, we've explored the design behind the RC2T damper, dug into the new technology behind Hydraulic Bottom Out, and now we've arrived at the DebonAir+ air spring.
During the "dream big" phase of our 2023 rear shock collection, the development team's vision was to design meaningful adjustments with tunability that significantly impact your ride experience. While looking at air springs, the team identified a way to expand our range of spring curves to optimize the different frame leverage rates out there and meet the diverse needs of riders. Our new DebonAir+ air spring for Super Deluxe and Deluxe includes two different air cans and two types of Tokens to help you dial in exactly how your air spring feels.
FIRST, LET'S TALK AIR SPRING THEORY.
Before we jump into air spring theory, we'd strongly suggest checking out the fork DebonAir+ article, specifically, the section "OK, So What Does An Air Spring Do?". In that article, we cover air spring theory that corresponds to rear shocks and will make it easier to follow here. Don't worry... we'll wait.
Ready? Let's dive right in!
Rear shocks look and function different than forks in that while they have both the air spring and damper, it's condensed into one contained package instead of in two different legs. In rear shocks, the air spring consists of an air can encompassing the damper and the Seal Head/Air Piston. As the name implies, the Seal Head/Air Piston serves two purposes: the seal head for the damper body and the air piston for the air spring.
As the rear shock compresses, the damper body moves up the damper shaft, propelling the Seal Head/Air Piston into the positive chamber of the air can. Like air springs in forks, when the air piston moves upwards through the stroke, it compresses the air molecules inside the positive air chamber to create pressure. Eventually, that pressure reaches a point where it counters the force from the compression event and forces the piston down. As with forks, we apply negative volume to the underside of the Seal Head/Air Piston to create equal pressure on each side of the piston to allow it to exist in a neutral position. With opposing forces on either side of the piston, the piston can move freely and easily. The positive and negative air chambers equalize via a dimple in the air can that allows the air to swap from positive to negative when the shock compresses, and negative back to positive during the Rebound stroke. [This is an essential part of why you'll want to cycle the rear shock a few times after servicing or adding air to your system—the chambers need to be equalized!]
Air can dimple
The volume of both the positive and negative chambers can be tweaked in the design process to affect the spring curve. A more linear curve takes more force to initiate movement but reaches full travel easier with more support in the mid-stroke. On the other hand, a more progressive curve means it's easier to initiate travel and ramps up the force needed to reach full travel at the end of the stroke. Previously, our aim was to cover as many bases as possible in the middle of those extremes.
SO WHAT’S NEW FOR 2023?
With our 2023 rear shock lineup, our goal was to design an air spring that optimized a frame's leverage rate to make the curve at the rear wheel as linear as possible: pairing progressive frames with linear spring rates and linear frames with progressive spring rates. That means that each frame manufacturer can choose the air can that will feel the best for their specific kinematics. From there, we added Negative Volume Tokens to our existing Bottomless Tokens to create steps between the air cans to help you perfectly tune your air spring.
One air can couldn't get us the complete range we wanted, so we introduced two air cans to work with more leverage rate curves—anywhere from the most linear to the most progressive.
–Lindsey Watson, Product Manager
The Linear air can has more balanced positive and negative air volumes and focuses on maintaining a consistent feel throughout the travel. The Linear can provides more support in small bumps and chatter while still allowing the rear shock to use full travel. We suggest pairing the Linear can with a progressive leverage rate frame to provide enough consistency through the stroke to allow the rear shock to use full travel.
The Progressive air can offers a greater negative air volume, making the negative spring effective for longer throughout the travel. Similar to the MegNeg air can, the Progressive air can makes it easier to get into the travel right off the bat. The increased negative volume also makes the end of the spring curve ramp up quickly, so it's harder to bottom out. We suggest pairing a Progressive can with a linear leverage rate frame to bolster end-stroke support and prevent bottoming out.
The chart below shows the air spring curves for the Linear and Progressive air cans. You can see that with the Linear air can, it takes more force to get into the travel but offers more mid-stroke support and less effort to reach bottom out. The Progressive curve shows that it takes less force to get into the travel, but the curve ramps up increasingly as it moves through the stroke, making it much more difficult to reach bottom out.
Progressive and Linear Air Spring Curves
Now, we want to make it super clear that if your rear shock came on your bike (not purchased aftermarket), your frame manufacturer selected your air can to match their specific kinematics, and we suggest leaving that air can on your rear shock.
Riders can also choose to adjust the volume of the positive and negative air chambers to fine-tune the feel of the air spring.
Bottomless Tokens—our positive air chamber tokens—affect the last 30% of travel and can be installed to ramp up spring rate, making it harder to bottom out while maintaining a lower air spring pressure. Finding it hard to reach full travel even when sag is correct? Remove a Token or two to make it easier to make the most of your travel. Air shocks can run 0-4 Tokens, depending on what works for you.
Negative Volume Token on the left, positive Bottomless Token on the right
Negative Volume Tokens reduce the negative air chamber's volume to decrease the negative spring's effectiveness. Install the Negative Volume Token to get a bit more traction off the top and more mid-stroke support, or leave it out of the mix to make it easier to initiate travel.
Bottomless and Negative Volume Tokens are compatible with each other and the Linear and Progressive air cans.
We designed the air spring to have even steps of increasing Negative volume, starting with the least: the Linear (L) can with a negative Token, to a L can without a Negative Token, then a Progressive (P) can with a Negative Token, and then a P can without the Negative Token.
–Dave Camp, Senior Design Engineer
Consistent with small bumps and chatter to playful and poppy, or somewhere in between, DebonAir+ allows the rider to determine precisely how their air spring will feel. Whatever bike you ride, the new DebonAir+ is here to help you go further than ever.
DebonAir+ Linear and Progressive air cans and Purple Bottomless and Negative Volume Tokens are only compatible with 2023 Super Deluxe Air and Deluxe Air. Make sure to check out the RockShox FAQ for any DebonAir+ questions.
Photos by Ian Collins, James Stokoe, and Nik Emerick. Renderings by Ray Bach. Words by Sarah Walter.