The Demo name has been in Specialized's lineup for nearly as long as riders have been building and sending moves that require such machines, and the bike has evolved over the years from something designed for freeriding to a low and slack bike meant for racing the clock on Sunday. But even though the geometry has matured drastically over that time, the five previous iterations all shared the same basic suspension layout, and its silhouette is one that's instantly recognizable by any mountain biker who's owned some baggy riding shorts or a full face helmet. 2015 sees Specialized make a wholesale change in the bike's design, however, and the result is a fresh looking 200mm travel, 650B wheeled downhill rig that is built almost entirely from carbon fiber and features a stunning one-sided seat mast that is sure to be even more polarizing than the wheel size the bike rolls on.
Just like the five previous Demo platforms that came before it, the 2015 Demo is the brainchild of Jason Chamberlain, Senior Design Engineer at Specialized, and his aims with the new design were much the same as with the previous race oriented Demo, but to also take them to the next level. "About two and a half years ago I started putting my ideas down, and the goals were lighter weight, better bump performance, and lower center of gravity," he said of those early thoughts. Those goals aren't too surprising given the Demo's intentions as a race machine, but it's the last objective on that list that had him considering moving away from the suspension layout that we all picture when we think of the Demo. He explained that the bike's concentric bottom bracket pivot is the result of wondering what the bike would look like if he moved the main pivot down a few inches from where you would otherwise expect to see it, and then reconfigured the rest of the pivot points accordingly. But while less weight and a lower center of gravity were areas that he wanted to improve on, his number one priority with the new bike was to have it carry momentum better. The 650B wheels and the improved angle of attack that they offer over 26" hoops greatly helps that cause, but, somewhat unexpectedly, it wasn't a foregone conclusion that the bike would roll on 'tweener wheels. "When it comes to wheel size, we explored everything: 26, 29, and 650B,'' he explained to Pinkbike when questioned about if a 29" wheeled downhill bike was ever in the cards. ''We think that for this platform, 650B is best because it give you a balance of light weight and quick wheel response, and also allows you to package the rear wheel in a short chain stay.
2015 Specialized Demo Details
• FACT 11m frame: carbon front and rear triangles, link • FACT 10m frame: carbon front triangle, seat stays, aluminum link and chain stays • Rear wheel travel: 200mm • Wheel size: 650B • New FSR suspension design • Revised Style-Specific Geometry • 63.5° head angle • 430mm chain stay • Ohlins TTX shock • Full 1.5'' head tube • Internal cable routing w/ interior guides • ISCG 05 chain guide tabs • BB30 bottom bracket • 12 x 135mm rear axle • Frame weight: 7.6lb (FACT 11m w/o shock) • Availability: January 2015 • MSRP: TBA
This is the sixth generation of the Demo platform and we've always had a lot of positive feedback on certain attributes of the bike, and we've tried to carry those on. Even though it's a radically new re-configuration, the heart of the performance is still very similar to the bike that people have known and loved for years.- Jason Chamberlain, Senior Design Engineer, Specialized
The topic of geometry, and especially chain stay length, is one that's hounded Specialized all year, mainly due to team rider Aaron Gwin experimenting with a longer rear end that was custom made for his race bike. And while it was certainly no secret that Gwin was looking for some added length to improve stability, likely due to his previous experience on longer bikes, his teammates seemed to be getting along just fine with the stock geometry. "When we brought Aaron on board last year we did a lot of research into geometry because he wanted a frame that he felt he could go fast on and something that he was familiar with, so we made a lot of options for him to race on,'' Chamberlain said of the in-season changes to Gwin's bike. ''Ultimately, we ended up with one single geometry that he felt fast on, but at the same time still honoured the geometry that Troy had been winning on before that. So now we have a bike with a longer chain stay by 10mm than the previous Demo, which is still, for a 650B bike, probably one of the shortest chain stays out there. We also keep the low bottom bracket that is very characteristic of Specialized bikes."
If there's one thing that might steal attention away from Specialized anticipated decision to go with 650B wheels, it would be the bike's single sided frame. Technically speaking, it's only the seat mast zone that has gone to a one-sided design, something that was made possible by this area no longer having to serve as home for the linkage to pivot off of, as well as Specialized's commitment to manufacturing the frame out of carbon fiber from the get-go rather than debuting an aluminum version first. ''With this new FSR layout we realized that the upper portion of the seat tube structure only does one thing: it holds up your seat post. We didn't need it to be as massive, and we didn't need the structure to straddle the shock like it had in the past,'' Chamberlain explains when questioned as to how the idea came about. That's all fine and dandy, but we had to ask why, especially when you consider that it doesn't seem to offer any sort of performance advantage. So, what's the point? "It allows the frame to be packaged very tight and very narrow, and it allows very easy access to the shock,'' a reference to a racer who may need to either easily reach the Ohlins TTX's dials or even make a shock swap in a hurry. A more important point is that it will likely mean that any shock made in the future, regardless of its silhouette, will fit the bike due to the clearance that the single sided design affords, especially because Chamberlain has also moved away from the clevis rearward shock mount system of the previous Demo.
The carbon fiber front triangle is molded in two sections - the seat mast and bottom bracket area, and the forward section of the triangle - and then bonded together afterwards, but the single sided design is also said to allow for simpler and more consistent construction methods due to a less complicated procedure in the molding process. Does it make for a lighter frame? Although the 2015 Demo S-Works FACT 11m frame, with its carbon front triangle, carbon link, and carbon chain and seat stays is claimed to weigh 7.6lb without a shock, which is nearly a full pound lighter than the previous Demo, Chamberlain did say that the single sided mast area likely saves only a marginal amount of weight. The FACT 10m frame features the same carbon fiber front triangle and carbon seat stays, but uses an aluminum link (which weighs 240 grams more than the carbon unit) and chain stay assembly.
Early sketches of possible 2015 Demo designs by Lead Industrial Designer Jamie Stafford, with the blue frame at center being close to the final design.
Suspension Design - The Same but Different
The previous iteration of the Demo that we're all familiar with, the design that led to oh-so-many jokes about surplus chain stays, was a four-bar, FSR layout with eight pivot locations (four on each side). Despite appearing to be quite different from that bike, the 2015 Demo also sports eight pivot locations and a four-bar, FSR layout that, according to Chamberlain, sports very similar kinematics and instant center location. That said, there's a pretty good chance that even your non-biking spouse would be able to tell you that the two designs look drastically different, likely followed by one of those eye rolling "what does it matter?" faces, as it's pretty obvious that Chamberlain and his team have done much more than a simple re-working of the Demo's back end. The asymmetrical design's main pivot rotates concentrically around the bottom bracket, and its 200mm of rear wheel travel is controlled via a custom tuned Ohlins TTX shock that Specialized says features less mid-speed compression for more control on initial impacts, but also increased high-speed compression damping for more control when pushing hard.
The new, 200mm travel Demo utilizes a revised suspension layout compared to the previous Demo platforms, but it's still a four-bar, FSR design.
Concentric Bottom Bracket Pivot - There has to be a good reason for Specialized to shrug off all of the expected Rotec comments that are no doubt going to come their way, and it turns out that reason is all about center of gravity and lowering its location compared to the old bike, which is the reason that the main pivot now calls the bottom bracket home rather than sitting up higher as is more common. Why is this important? It's probably simplest to explain it in exaggerated terms: picture yourself holding a 10ft long pole that has a 20lb weight on the end and then holding it out in front of you and swinging it back and forth. Now do the same thing with a 5ft long pole with the same weight - it's not only easier to start the swinging motion with the shorter pole, it also takes a lot less effort to change its direction from left to right. What the hell does that have to do with mountain bikes? Well, the pole is the bike and the weight is its suspension components, which are the heaviest part of the frame. The lower those components sit (the shorter the pole), the easier it will be to move the bike around. Yes, we're talking small percentages here, not game changing stuff, but there's no doubting that the new bike features a lower COG than the Demo we're all familiar with. "I started by thinking about what it would look like if we just moved everything down three inches, and naturally what happened was that the main pivot moved into the same real estate as the bottom bracket, so it became natural to just integrate those into one pivot,'' Chamberlain explained about the design. ''Then I reconfigured all the other pivots around that. The FSR, four-bar performance is still there even though the pivots are in radically different locations."
The bike's main pivot rotates concentrically around the bottom bracket, with the pivot axle also serving as home to the BB30 bottom bracket bearings.
Does the concentric pivot dictate the axle path, though? And couldn't you easily run it as a single speed setup due to the lack of chain growth? Sorry, wrong on both accounts. The rear axle isn't located on the chain stays, but rather on the seat stays that pivot off of the chain stay, meaning that the path of the axle is a separate deal that's not tied into the concentric main pivot. And speaking of axle path, Chamberlain wasn't sold on the idea of a drastically rearward trajectory in the never ending search for better momentum carrying abilities, a topic that seems to make up much of the word count in many reviews and marketing spiels relating to a lot of downhill bikes: ''At the onset of this project we purchased every bike out there with every imaginable wheel path so that we could really understand them,'' he said when questioned on the subject. ''We filmed them all from the side with high-speed film and really got an idea about what bikes did what. What we found was that we could achieve the same level of performance through a properly tuned FSR with an Ohlins shock as you could with some of the radical designs with crazy wheel paths.'' He went on to cite the drastic geometry changes, possible chain tension issues, and also difficulty lifting the front end for a manual due to the lengthening rear end as it compresses as all being valid reasons for tackling the momentum carrying challenge from different angles.
Going with a concentric main pivot wasn't without its challenges, however, as it means that the area around the bottom bracket becomes much more complicated than a more traditional layout. First, the massive main pivot bearings - there's one on each side of the shell - are pressed into machined aluminum bores, with a milled out spacer in between for each bearing's inner race to come up against. The pivot axle is equally massive, having to run through the swing arm and thread into the non-drive side, and it also serves as home to the BB30 bottom bracket bearings that the bike uses. Oh, and because the carbon swing arm rotates around the bottom bracket shell, Specialized has been able to locate the bike's ISCG 05 chain guide tabs on it, thereby allowing the guide to follow the movement of the rear axle and chain as the bike goes through its travel.
The Demo's revised suspension layout presented a few fresh challenges to the design team, especially when talking about lateral rigidity. The goal was not to make a stiffer bike than what they already had, however, only to equal the numbers of the existing Demo - too rigid and a bike can feel harsh, especially when leaned over in a corner and on an angle that doesn't allow the suspension to absorb the ground. And while you might assume that matching the current Demo shouldn't have been a difficult task, a look at the new layout from above shows that the left and ride side seat stays are actually completely separate units that are no longer tied together with a bridge over the tire like on the old design, meaning that matching the old bike in term of stiffness might not be such an easy job. Specialized approached the challenge from two different directions, literally, with a new keyed 12 x 135mm thru-axle at one end, and a massive rocker link at the other.
The less expensive Demo 8 I Carbon uses an aluminum link (left), while the S-Works model sports a carbon fiber version that Specialized claims saves a whopping 240 grams.
Rocker Link - The previous design saw the shock actuated essentially by the swing arm itself, with just a short clevis between the two, while this new layout has the shock being compressed by the rocker link. That's not the rocker link's only job, though, as it replaces about a third of the length of the seat stays stays as well and also must play a significant role in the frame's lateral rigidity. There are two versions of the link; a hollow carbon unit coming stock on the high-end bike and frame kit, and an aluminum version that weighs 240 grams more being utilized on the less expensive Demo 8 I Carbon. The carbon link might look relatively simple, but it's actually a mostly hollow piece with internal carbon ribs that are strategically placed to increase both strength and rigidity. Tight confines are tricky when it comes to being able to compact the carbon enough to remove any voids in the walls, which is why the cutaway of the link shown below reveals small amounts of foam in such places, and each pivot location features aluminum bearing journals rather than having the sealed bearings be pressed directly into the carbon.
A look inside the carbon rocker link shows the internal ribbing that helps increase rigidity and strength (left), and the foam elements can also be seen in the tighter confines (right).
Proper alignment is critical given that the link plays such a major role on the frame, and adding the aluminum bearing journals after manufacturing the link wouldn't guarantee that it would be up to spec. The answer was to install the still un-machined aluminum components during the molding process, with the carbon completely covering each of the small separate aluminum sections before being machined away along with all but only the minimum amount of metal required to serve as home for each bearing. The whole process ensures that not only is each bearing journal in perfect alignment, but also as piece of mind when it comes to replacing pivot bearings down the road that they won't need to be pressed in and out of fragile carbon bores.
L7 Square Axle - The job of upping frame rigidity doesn't fall on the rocker link's shoulders alone, with Specialized employing a keyed 12 x 135mm thru-axle at the other end that they say helps to have the new Demo match the older design when put to the test. Non-round thru-axles are nothing new, of course, but Specialized referring to the axle as being square is a bit misleading as it's round for its entire length except for each end, and it is compatible with any 12 x 135mm hub. It sports a square, conical shape to each end that nests into the frame to better tie the left and right seat stay assemblies together.
A square, conical end to the axle sees it key into the frame to minimize flex (left). A small aluminum guard can be seen at the end of the non-drive side chain stay, an addition that has been made to protect the carbon from the disc rotor when removing and installing the wheel.
Specialized feels that seat tube length should have next to nothing to do with downhill bike sizing, and that choosing the correct size for you should come down more to top tube length and reach than anything else. This approach makes a lot of sense and is one that you'll find in the BMX and dirt jump worlds where handling and being able to throw the bike around means everything and proper leg extension counts for nothing. They feel that the same principles apply to downhill bikes, and that as long as the seat tube is low enough to afford enough clearance, the bike's length should be the deciding factor when it comes to sizing. Style-Specific Sizing, or S3 geometry for short, is the realization of this, with the new Demo being available with four different top top lengths that are split between two relatively short seat tube heights.
The idea behind S3 is to allow the consumer to choose the size that best suits their riding style and terrain. For instance, at 5' 9" I've often found that I can ride either a medium or large traditionally sized bike but usually prefer to go with the longer option due to the added stability of its stretched out wheelbase. Specialized calls their sizes short, medium, long, and extra-long, and if I was looking for a more lively, playful machine I might prefer the medium length Demo. Team rider Mitch Ropelato, at 5' 8", goes with the medium for this exact reason, but Gwin says that he prefers the long for its more stable wheelbase, despite being the same height as Mitch. Specialized Development Rider Brad Benedict is 6' 1" and reaches for a long Demo for days in the park but an extra-long for race weekends. The two seat tube lengths - 394mm for the short and medium, 419mm for the long and extra-long - are both short enough to even allow a relatively small rider to try out a longer bike if they're really looking for that added predictability that comes from a long wheelbase.
S-Works Demo 8
Demo 8 I Carbon
S-Works Demo 8 Frame
That's a load of information to digest, especially when all that really counts is how the 2015 Demo performs on the trail. We'll be spending the next two days in the Whistler Bike Park with both a brand new 2015 Demo and last year's Demo to find out exactly how it's different from the old bike, so stay tuned for a comparison article that goes well beyond the usual "First Ride" impressions.