​The Ultimate Guide to 'Metric' Shock Sizing and the RockShox Super Deluxe 21

For over two years RockShox has been quietly working on a major project they feel will take mountain bike rear suspension to the next level, and today they draw back the curtain. What we present to you here is an in-depth guide to the new "metric" shock and hardware sizing, a close look at the new RockShox Super Deluxe shock that capitalizes on that sizing, and our personal impressions following multiple back-to-back test sessions on the trail. We also provide the important answers as to why things are happening.

Why should you care? Because bikes are changing moving forward, this movement is backed by several big companies, and many parts of it are still misunderstood. It won't be an overnight change, but a few years from now every bike may use what's discussed in this feature. While RockShox straight up says this isn't one, metric is essentially a new standard - one created to eliminate current constraints and limitations in order to create the best shocks possible.

There's a lot to digest, but by bringing you the full picture we hope we're able to answer your questions and more. It's time to really dig in...

What Is Metric?

Last week a press release was issued by RockShox, DVO, Cane Creek, Manitou, SR Suntour, and X-Fusion indicating that we will see several new rear shock lengths and fitment options starting in 2017. These new shock sizes "are based on metric dimensions" and said to "provide performance benefits to suspension and frame designs."

Due to some confusion over the term "metric" and a poorly timed release around April Fools' Day, the internet went ablaze with comments like: "I thought my shock was already measured in metric? Do they need a calculator?" "This has to be a joke." "Conspiracy, I say!"

Well, it's not a joke at all (or a conspiracy). As we wrote in our response to the press release, shocks have been produced in several convenient imperial eye-to-eye and stroke sizes for years (6.5x1.5", 7.875x2.0", 8.5x2.5", etc). While these numbers can certainly be converted to the metric system using some simple math (1" = 25.4mm, ya dummy), "metric" isn't just a switch in listed dimensions, and this whole thing has little to do with metric versus imperial systems. "Metric," as it's referred to here, is actually a new set of sizes for rear shocks that have been agreed upon by several suspension and frame manufacturers. That means new eye-to-eye and stroke measurements in conveniently chosen increments of millimeters.

Metric Shock Sizing

The metric sizes outlined below look a bit more logical, don't they? The new sizing falls on 5mm stroke and 20mm eye-to-eye increments, and you'll notice lengthened eye-to-eye measurements for each stroke length. If a frame designer wants to limit the travel or reduce the stroke, they can do so in 2.5mm increments.

According to Chris Mandell, RockShox Rear Shock Product Manager, "This is the first real effort to look at the needs of the frame designer and the end user, and to organize a system from the shortest travel bikes to the longest travel bikes to get a coherent, progressive shock sizing system... and a shock that will deal with what we're doing with bikes today."

Metric is currently focused on trail and all-mountain/enduro sizing which makes up the bulk of the market, but RockShox indicated that they're experimenting with longer versions for downhill bikes as well.

Trunnion Mounts

What's this trunnion thing? Not every frame can accommodate a longer shock, especially on smaller sizes that need super low standovers. Trunnion shortens the required eye-to-eye length 25mm by running the upper mounting hardware through the shock body, but still provides shock designers some added benefits inside. Visually they're similar to what Trek has been doing on their bikes for years.

How Did Metric Begin?

To understand how this all began and why RockShox feels it's needed, we spoke with RockShox Design Engineer Tim Lynch:

"This project started out in a conversation with [Jeremiah] Boobar. He laid it out to me, 'Hey, we really love what we were able to do with Pike, what's it going to take to do that in a rear shock?' I had been dreaming about this kind of stuff for a while, so my immediate answer was we're going to need to change the standard eye-to-eyes and strokes that everyone is familiar with. We talked it through and sorted out who that would affect and if that was something they could tolerate. I'd say it took a decent amount of courage on his part to take this project on. It really has given us the chance to do cool things with a little bit more space."

That last bit contains the key to this whole thing - "a little bit more space." In order to create a shock on par with the ultra smooth performance of the Pike fork, RockShox needed more room to work inside the shock. While most of us just see the relatively simple outside appearance of a shock, what goes on internally is very complicated and every millimeter is precious.

And so began the task of determining how to add more space inside a shock in a logical manner that not only benefitted shock design, but RockShox's biggest customers (frame manufacturers) as well.

How Did The Current System Come To Be?

If we look back at how the current shock sizes came to be, it starts to sound like a bit of a free-for-all. Several years ago, as early full suspension bikes went from being an odd thing to something people saw as a real benefit, the demand for more travel began. To meet those longer travel needs, bike companies would design a new frame and determine that a shock of X by Z dimensions would likely get the job done. Then they'd call up RockShox or another suspension manufacturer to tell them what size they needed. If the company was ready to place a big enough order, RockShox made it.

Then, months later, when a different bike company saw it and asked for the same size RockShox would make more. The cycle continued for several years and that's essentially how we ended up where we are today. Of course there has been some refinement along the way, but even now we see proprietary shock sizes popping up left and right. RockShox admits the current system was basically a result of several single-serving conversations.

Shortsighted? Possibly so, although you have to admit the bike industry is still in its infancy. All those years have allowed RockShox to learn what works best inside a shock and frame designers to come up with much better designs. One big goal with metric is to create a more universal solution that also looks at the needs of frame designers.

Metric Hardware Sizing

Just like shock sizes, the vast array of hardware sizes is also a result of ad hoc conversations and needs. "You'd like slightly narrower hardware because the finish on your frame was too thick? Okay, we can do that." "You'd like another size because it allows your rocker to just fit around your seat tube? Deal."

While frame companies have no doubt improved their tolerances over time, things were a little rough years ago, and the number of hardware options spiraled out of control. Metric provides a much simpler solution for the end user (that's you), and if you've ever been into a bike shop in search of shock hardware you'll surely appreciate this move.

The new system provides standard hardware widths in 5mm increments, and reduces mounting hardware options from 80 to 18.

Introducing Super Deluxe And Deluxe

Now that you know how metric began and what sizes are available, let's explore several ways RockShox is using that extra space to create better shocks. The new Super Deluxe and Deluxe air shocks address several design limitations, issues, and restrictions for improved performance.

More Bushing Overlap

"The regular handshake is kind of weak, but the super bro handshake is much stronger. It's not rocket science." - Tim Lynch

Every shock relies on bushings to keep the shaft centered relative to the body, and the shaft glides in and out along the bushings. The distance between two bushings is known as bushing overlap. When that distance is small, binding can occur under lateral loads. Of course bike manufacturers do their best to prevent the shock from seeing these loads by making stiff frames, but it still occurs to a large extent on some designs. This can result in worn out shock components, leaking, etc.

By increasing the overlap you make the shock more resistant to binding, which results in better traction and improved durability. The Super Deluxe has 20mm of air can bushing overlap (blue arrows) versus 15mm on the Monarch Plus. That's a 33% increase. The piston/sealhead bushings (green arrows) see an increase from 9.3mm to 17.7mm, or 90%.

On trail this is most noticeable near top out when there's side loading in the frame, like when you're coming into a corner unweighted and looking for traction. With more overlap the shaft moves easier as your wheel touches the ground.

Simplified, Consistent Air Spring

Every shock needs to be tuned to its frame. When a new frame is being made, the designer will send the kinematics to RockShox, who will then upload it into a sophisticated in-house program that spits out a recommended starting tune. This recommendation is based on many years of previous tunes on thousands of bikes, and typically gets them close to the desired ride feel. After some experimentation and ride testing by the frame company, RockShox will then visit the company to dial in the final tune by doing back-to-back runs on the company's preferred trails. In addition to figuring out various damping settings, part of this process is dialing in the air spring. Previously this meant choosing from a myriad of combinations involving two eyelets, three air cans, and a wide range of volume spacers. That's a lot of possible combinations.

The design of the Super Deluxe and Deluxe makes life easier as a frame designer because they reduce the number of options to two air cans (SoloAir and DebonAir) and a range of red-colored volume spacers (now called Tokens, like in their forks). As a rider this means you're more likely to get a shock and frame combo that really works. It also means getting a replacement shock will be easier if it's needed. We often talk about suspension performance in our bike reviews here on Vital MTB, and the chosen air spring has a big impact on that ride quality.

Picking the right air spring volume has a lot to do with how much progression (rise) a frame's suspension design has. Bikes that have a flat rate typically need small air volumes to resist harsh bottom-outs, and ultra rampy bikes need a high volume or riders may struggle to get full travel. With a huge range of suspension designs on the market, shocks need to work for a lot of bikes. Thanks to a machined eyelet, the Super Deluxe DebonAir volume is equivalent to a Monarch Plus DebonAir with a high volume eyelet, but can easily be reduced to the other side of the range using Tokens.

On a similar note, if a frame designer chooses to limit the stroke, the limiter automatically adjusts the air spring so it's consistent between sizes.

Another factor that can drastically impact a shock's total spring curve is the pressure behind the internal floating piston (IFP). It turns out the popular inline 7.875x2.25" (200x57mm) shock size - which originated at frame designers' requests - is so tightly packed inside that there is very little room for this charge to compress near bottom out (blue arrow). This results in a huge and unfavorable addition to the spring curve in a super rampy way.

Thanks to metric sizing, the inline Deluxe shock now has consistent room for gas compression across all sizes. This was actually a major driver of the sizes ultimately chosen. In combination with the air spring design, consistent gas compression room keeps the spring curve the same from shock to shock, size to size. All this consistency means it's easier to design suites of bikes, from short to long travel, that behave in a similar fashion. Previously designers had to consider how individual shock sizes interacted with a frame's kinematics, which made it more difficult and complicated than it needs to be.

Less Friction With Bearings Mounts

RockShox claims they've created "the world’s lowest-friction shock" with the Super Deluxe. That's a big claim, but they've done the lab tests to ensure the claim is true - this includes static (breakaway) and kinetic friction. A major part of that friction reduction is a new bearing mount system.

For years frame designers have been trying to eliminate friction in the rear end of their bikes, and we've seen many bikes go from bushings to bearings in the pivots, so it's only fitting that the rear shock mount is the next progression to ensure the most friction-free and supple suspension possible.

As a bike's suspension is compressed there is often a lot of rotation at one of the two shock mounts. If you watch the linkage relative to the shock as the shock compresses you'll notice a big change in their relative angles. Most shocks currently rely on a bushings at the two mounts. Bushings + rotation = friction.

The new shocks have the option for integrated bearing mounts at both the body and shaft ends, though most bikes will be spec'd with a bearing mount only at the end with the highest rotation. If it's a trunnion mount the bearings go in the frame. Didn't Trek and Giant already put them in the frame? Yeah, on some models, and for good reason:

So why not use spherical bearings or needle bearings? It comes down to durability and availability. The bearings spec'd by RockShox have expected lifetimes comparable to those already used in your frame, and are readily available around the world in any bearing shop. If you don't feel like replacing the bearings by pressing them out, the whole bearing mount assembly can be easily replaced and comes with fresh bearings pre-installed.

Why couldn't the bearings and new hardware have been integrated into existing shock sizes? They likely could have been, though RockShox would be asking nearly the same thing of bike designers at that point (new frame mounts, etc).

Improved Damping Technologies

With all that friction gone thanks to the bearings and extra bushing overlap, the shock is now able to operate more freely. Oddly, reducing friction can actually make a bike feel less controlled unless the damping effect it had is replaced by actual compression and rebound damping. This is a great opportunity though, because - as anyone with a bone dry fork will attest - friction is the worst way you can damp a system because it's inconsistent and sticky. Damping inside the shock itself is much better.

RockShox now adds extra low- and mid-speed compression damping to their metric shocks. The high-speed compression remains very similar to avoid spiking issues, and friction is less of an issue at higher rates. This extra damping adds to the ride feel by helping you stay in control and improves acceleration while pumping, among other things.

Rebound damping is added, too, through a toned down version of RockShox's Rapid Recovery system that's a little more linear and less digressive (a touch slower deep in the travel).

Aside from simply adding damping, RockShox is using the extra space to develop how they damp the shock. On the Monarch Plus the system is "unchecked," meaning some compression fluid can flow back through the rebound circuit, effectively but momentarily killing your low-speed compression control. The new Super Deluxe has several checks to control how and where oil is flowing, and the new damper has dedicated mid and lock compression pistons. There's no crossover or compromise between compression and rebound, which was a common problem on older shocks as you'd close the rebound and shut off free-bleed in the system, impacting low-speed compression.

Thanks to the new three-piston design, bike companies can now pick the tunes for each compression mode (open, pedal/medium, and climb/lock) . There are four open compression tunes, two pedal compression tunes, one climb compression tune, and three rebound tunes.

With all this talk of air shocks, what could theoretically be improved in a coil shock? For starters, RockShox's 8.75x2.75" (222x70mm) coil shock faces a similar space deficiency which leaves designers worrying about how many shims they can put on the piston and still fit everything inside. More space here is again a good thing. Coil shocks can also improve from added bushing overlap, and there's a chance to work a similar system of rebound checks into place to rid the shock of free-bleed issues.

Other Features

Other notable updates to the Super Deluxe and Deluxe shocks include:

• Larger diameter damper shaft - This increases oil flow and compression control.
• Improved scraper seal - The scraper seal (the one you see at the base of the body) is larger, more durable, and works better in cold temperatures.
• RockShox's Counter Measure technology - This spring system opposes the effect of IFP pressure, lowering initial breakaway force.
• New rebound dial - The new design on the Super Deluxe avoids compromises frame designers previously had to make to gain access to the rebound knob, but is still tool free.

Super Deluxe And Deluxe Specs

New Bikes On The Horizon

RockShox has been making a metric push at the OE (bike company) level for close to two years, which means some early adopters will likely have production bikes using the new shocks available between now and June, 2016. We've been asked to stay hush about specific names for now, but we know of 15 bike companies that plan to use metric shocks on their 2017 models, and a good handful of brands beyond that who have expressed lots of interest. Some of these brands are very popular among riders.

We do get the sense that some frame designers still haven't fully wrapped their head around what RockShox is selling, though, so some companies may be far behind. Development cycles on bikes are around 18 months depending on the brand.

The biggest pushback has been from small bike brands due to limited resources. These new shock sizes will require new carbon molds for many frames (not cheap), and manpower is limited. Bikes that simply require a new link, like the Transition Patrol we tested below, will be much easier to produce with a metric shock.

On The Trail

We had the opportunity to test the new metric sizing and RockShox Super Deluxe during a three day ride camp in rainy North Vancouver, and have continued to test the shock in recent weeks in Arizona.

Transition's Patrol served as pretty much a best case scenario for trying this system out. It has lots of bushing rotation at the top mount and there's room for a longer shock, provided it was equipped with a new link.

The replacement test links were designed by Transition and machined by RockShox. Changing it out resulted in very similar kinematics (there's just 2mm stroke difference in the 216x63mm to 230x65mm shocks), which allowed our back-to-back tests to hone in on the shock and mounting performance.

Will there be less noticeable differences on a bike with less bushing rotation? Possibly, but keep in mind that all bikes will benefit from the tech discussed above, and bikes that put stresses on the shock as a structural member will really benefit from the added bushing overlap.

We started our first back-to-back test with a RockShox Monarch Plus RC3 DebonAir installed, rode several trails to the point that we were very familiar with them, then swapped out for the Super Deluxe RC3 DebonAir. Both shocks used the medium open compression tune, and both shocks were set to 33% sag.

At the end of the day our on trail experience spoke volumes. Thanks to the performance of the new Lyrik fork and Super Deluxe, we were able to overcome a fear of (most) wet roots and rocks that previously scared the bejebus out of us. We're desert rats at heart, grew up in dusty and dry conditions, and the ability of the equipment to provide traction in conditions where we didn't think any existed was nothing short of impressive.

On repeat laps of Pingu, a rowdy North Shore trail, switching from the Monarch Plus made a few things immediately apparent. The trail starts off with three consecutive drops into a very rocky entrance to a right hand turn where having your stuff together is really important. With the new system installed there was gobs more control coming into that turn, and the bike just seemed quieter and wasn't dancing about beneath us. That quiet feel and added chassis stability allowed us to ride a little bit harder and try new gaps along the root and rock infested trail.

While the DebonAir can does a very good job of improving off the top compliance on the Monarch Plus, the Super Deluxe felt better deeper into the stroke with a smoother, more consistent feel, which again helped create traction in scenarios when we previously wouldn't have counted on any. By the end of the trip we were willingly hucking into and over roots without abandon just to see what we could get away with.

The added compression damping had a very positive effect on the bike, too, and we appreciated the speed and stability gains while pumping, jumping, and turning.

Another area that an improvement was very evident was on slippery climbs. We were impressed by the shock's ability to help keep the rear tire on the ground. It's something that we noticed as we were able to make more climbs than before, whereas previously when we'd be putting power down we'd occasionally get slight hops in the rear wheel and momentarily lose traction and momentum. As a result of the traction provided by the new system, consistent power transfer made tricky climbs seem easier. The middle pedal compression setting also seemed easier on our ass, with a firm but dead feeling that was able to conform to the ground better without hopping about.

Back on Mingus Mountain in Arizona we did several back-to-back laps on a downhill bike worthy trail littered with high-speed, full-on rock gardens that require you to stay on your toes at all times. It's the type of trail where slight but precise side-to-side movements are needed to hit the good lines and stay in control. Again, the quietness of the bike allowed us to ride more comfortably, and we were able to ride sections smoother with the new shock.

With the Monarch Plus we occasionally felt firm but subtle kicking sensations as the rear end would pitch us forward ever so slightly. This typically occurred when coming off a fast, smooth section as we'd pull back to hit the first rock of many, and would continue to occur when jumping through the rocks rather than staying down in travel. The little kicks throw you off ever so slightly. This isn't a huge deal - we've dealt with them for years - but when you experience the new system with the bearing and improved shock there's definitely an improvement that could be blindly identified.

Braking traction also felt far better with new shock as a result of its smooth feel and ability to keep wheel on the ground. Rough off-camber corners were met with improved rear wheel wheel traction as well.

We also noted that we consistently used more travel on the Monarch Plus by about 10-15%. Even though we were using more travel on the old shock it often felt rougher and less controlled.

At our final rebound settings for both shocks (they started very similar), we found that the Super Deluxe has a slower feeling rebound when bouncing on the saddle, but it works like a charm on the trail.

We overheard a quote from Adam Billinghurst, who tested the shock last year, that summed up our experience well: "I ride these trails every day, and I feel like I've got this stuff wired, but this just opened my eyes to a whole different world."

Are There Any Downsides?

It can't all be sunshine and butterflies, can it? No. In our minds these are the biggest negatives with metric:

It's bigger - This means bike frames will have to change, and accommodating the longer shocks could be difficult on some bikes. Frames that previously worked with water bottles may not anymore, for example.

It weighs more - Our 230x65mm Super Deluxe RC3 DebonAir and 216x63mm Monarch Plus RC3 DebonAir test shocks weighed in at 480g and 410g, and the links+shocks weighed in at 850g and 750g. That's with an upper bearing mount on the Super Deluxe, which likely adds a bit of weight in exchange for a big performance gain.

It might cost more - We weren't given prices, but bearings and new tech can't be cheap. We do think that RockShox's consolidation of parts and resulting higher volumes could get close to evening things out, however.

It doesn't fit your current ride - This is a future bike thing. While we were able to test the shock on an existing bike, it's unlikely that many companies will offer retrofit kits to work with these shocks. Plus, many bikes will need to be redesigned.

Things will be more complicated, at least for now - While the long term intent is to simplify things with fewer hardware sizes, air cans, stroke lengths, etc, for a minimum of 3-5 years companies, riders, and shops will have to juggle the old and new sizes of shocks and hardware.

If demand drops, aftermarket options may be limited for existing frames - RockShox and the other suspension companies committed to making metric shocks will make the current size shocks "until demand dies." In reality the aftermarket is tiny, though, so for these to continue demand will likely have to come from bike makers, meaning they wouldn't be using the latest tech.

It may not improve every shock - Suspension companies like FOX and Push (who will also make metric shocks) have worked hard to fit within the existing package and to optimize their designs around the current sizes. It's possible that not all will see a true improvement in their designs as a result of the extra space, though there may be some unrealized potential. Over the coming months we'll no doubt see many new shocks.

It may not help every suspension brand - RockShox obviously has a nice, pretty, streamlined package to offer their customers. While other suspension brands were told long ago about the new sizing, and many agreed to it, others may have some catching up to do. Smaller suspension companies may also struggle with having to make more shock sizes in the short term.

What's The Bottom Line?

"Would you like a DebonAir to go on that DebonAir?" That's basically how the new Super Deluxe feels on trail. As far as our riding experience goes, there is no doubt in our minds that the new shock and metric sizing that made it possible offer better performance. We often talk about bikes that suffer from off the top issues, and we think that we'll see far fewer of those bikes if they adopt this system. Bikes that were previously firm will now feel supple, and those that were supple will flat out feel amazing.

Are the issues outlined in this article limited to just RockShox designs? Do other brands' shocks face similar limitations? Can they also add a noticeable increase in performance as a result of the extra space? As we all well know, the ways in which each brand chooses to utilize the space available to them varies depending on their technologies and design goals. Whether or not it's a benefit to them (or their customers) is the crux to this whole metric thing really taking off or not, and one we'll have to wait and see. Given RockShox's execution, however, we know there's promise for every brand. What lies ahead is a transition period, and whether or not this new system is fully adopted by the industry will likely take a few years to sort out.

This feels like a genuine attempt to improve things for all, but much will have to change to make it happen. Ten years from now we hope to see RockShox's vision come to life as it will make things simpler in the long run.

Visit www.rockshox.com for additional details, and be sure to check out their Decimals story for more info.

Feature by Brandon Turman // Photos by Adrian Marcoux and Brandon Turman