In recent times we've seen the infiltration of more aggressive geometry into bikes with shorter and shorter travel. The current crop of trail bikes is as capable as ever. But what happens when you take some of that geometry recipe and sprinkle it on something with even less travel?
XC bikes have been getting a bit more aggressive in recent years as a response to the tougher tracks. But perhaps not quick enough for the Swiss brand ARC8. In the same way that Mike Levy used his crystal ball to predict the geometry of the future with the Grim Donut, ARC8 looked into their, arguably clearer, crystal ball to see what XC bikes of the future could look like
Evolve FS Details
• 29" wheels
• Carbon fiber front & rear triangles
• Slider suspension
• 100mm - 110mm rear travel
• 100mm - 120mm front travel
• M and L sizes
• 1775g frame weight (actual, size L, with shock)
• Bike Pricing: €5,999 to €9,999
• Frame Pricing: €3,299
What they saw was not only truly aggressive geometry for an XC bike, but some innovative solutions to suspension, manufacture and bike segmentation. The result is the Evolve FS.
The bike that started ARC8, the Essential, was done back in 2016, long before the public ever laid eyes on it. It was designed to be an aggressive trail bike for the time, and while it delivered on that it also turned out to be quite an efficient and light package that saw quite some action in XC racing.
Since then, XC has been evolving (no pun intended). Scott’s latest iteration of the Spark boasts 120mm of travel in a field of race bikes that still cling to 100mm. Wider tires and dropper posts are bringing the bikes closer to the average person’s mountain bike, ridden weekend after weekend all over the hills and forests.
At the same time that XC was embracing, well, less XC things, certain media people were also coining phrases and inadvertently defining new categories of bike. While the downcountry tag may be new, these bikes have been existing for much longer. Taking an XC bike and making it more capable on the downs isn’t anything new. When I worked for Scott I did the same with a previous generation Spark and loved the results. Jonas, founder of ARC8, enjoyed this too, riding a beefed up BMC XC bike for years before down country was ever a market segment.
All these thoughts of XC progression and downcountry were whirling round the minds at ARC8 prior to starting the development of the Evolve. One more was the slow, but consistent, infiltration of aggressive geometry into shorter travel bikes. Perhaps this is where ARC8 used its relatively small size to its advantage. Instead of slackening the head angle just a touch, or adding a couple of mms to the reach, they went all in.
They decided on a geometry that really stands out in this travel bracket but is something they believe might be the resting point for XC bikes in the future, going even further to say that they believe there will be no border between the two categories. Their thought, and maybe hope, is that bikes like the Evolve will be the XC race bikes of the future.
I rode a lot of XC during my tenure at Scott, even dabbling in a few XC races here and there. The infamous Lunchtime World Cup was nothing short of a battle each day that could rival the live stream of any race weekend. And if the ARC8 Evolve represents the future of XC racing, then boy are we in for a treat.
Frame Development & Details
Weight is still the priority of XC race bikes. Well, I thought it was but then we started to stuff everything inside the frame and now I’m not so sure anymore.
Either way, ARC8 put it pretty high up their list and used all the tools in their toolbox to shed as much weight as possible. The original Essential wasn’t designed as an XC bike but ended up being competitively light while having a very low number of warranty cases. So ARC8 used it as a starting point. And with very few warranty cases over the years, there was big confidence in their production partner to push the limits of lightweight manufacturing.
Reducing the surface area of a frame is a good way to drop the weight. It has to go hand in hand with balancing stiffness, strength, design and manufacturability, but reducing the surface area by 11% in the front triangle and 22% in the rear triangle compared to the Essential gave an expected weight reduction of 253g in carbon material and paint alone.
You can also drop the weight by using a thinner walled structure or using a less dense material, but there’s not much available at the moment that’s less dense than carbon fibre composite, while still being suitable to a mountain bike's manufacture and use. And paper-thin walls on a mountain bike are definitely not a good idea.
Simplifying the design of the Essential opened the door to shedding even more weight. Eliminating as much pivot hardware as possible is a low hanging fruit that ARC8 grabbed with both hands. The ten bearings on the Essential was dropped to just two 61902s on the Evolve. And combined with the slider being such a compact little item, all told the drop in hardware came to 118g over the Essential.
With the weight falling off faster than early freeriders on skinnie, ARC8 tried not to lose sight of making something that is easy to manufacture. Designing the bike to be made from carbon fibre composite from the beginning, along with knowing their production partner inside and out meant that ARC8 could take further advantage of using the internal pressure created by the bag or bladder inside of the frame to compact the composite evenly and cleanly during moulding. This gave them a frame with less complexity, less potential for manufacturing errors and less material needed to suit the process of moulding using external pressure from the mould or mould inserts.
The main pivot area is a good example - moulded as a closed structure from only internal pressure with the window for the chainstay being machined after the mainframe is moulded. The brake mount area on the chainstay uses the same idea, not relying on aluminum inserts and bulk moulding compound but creating a hollow structure that is post machined to suit the flat mount standard that the Evolve uses.
Frame stiffness also remained high up on the priority list while all this weight was being shed. It’s all too easy to make a really light wet noodle of a bike. Designing around a 55mm chain line allowed the main pivot to grow in width by 60%, even with fitting a 38T chainring. The dinky little slider also played its part, providing quite a boost in stiffness when compared to a linkage big enough to provide the same smooth suspension curves, and allowing ARC8 to take away the seat stay bridge.
With intensive FEA and computer analysis of the layup schedule, the cross-sections of the frame were reduced in areas that had less impact on the overall stiffness of the bike, like the seatstays. However, it’s not as cut and dry as bigger is stiffer and smaller is weaker. With XC bikes using such lightweight structures that common thought starts to fade. Taking into account buckling and the change of shape under load, ARC8 actually used smaller cross sections with thicker walls to give better stiffness and strength in the areas where this common idea of bigger means better didn’t play out. They even shaped the down tube in such a way to stop it from holding excessive amounts of mud.
Overall, they managed to drop the weight by 35% on what was already quite a light frame without sacrificing strength or stiffness. But when comparing the ridiculously low weight of 1775g without shock to the rest of the XC race bikes out there, it seems ARC8 has pulled the pants down on some of the biggest brands in the business while they were all perhaps too concerned about design.
On the scales the size L Evolve came in at just 1775g with a Fox Float DPS shock. That’s lighter than the claimed weights of the Specialized Epic (1869g), Cannondale Scalpel (1910g), Trek Supercaliber (1933g) as well as current (1870g) and previous (1799g) generations of the Scott Spark.
Without any absolute madness is the build specs, that allowed ARC8 to build an off-the-shelf XC race bike at 9.585kg (21.1 lb) with a dropper post and a good dollop of tubeless sealant. That's just over 600g lighter than some of the Scott Spark race bikes that line up to the World Cups. Even with a full Shimano XT build the bike only weighs in at 10.7kg. And this is with frame geometry essentially comparing to an XL size from other brands, which makes it all the more impressive.
With the slider mechanism tucked up against the top tube, it allowed for two water bottles inside the mainframe. There’s even a threaded BB for ease of use and provisions for a chain guide. To top it all off, there’s a SRAM UDH out back and a 30.9mm diameter seat post with 245mm max insertion ready to take a dropper post.
Perhaps the only gripe about the Evolve is the internal cable routing through the headset, something that many of us, in and out of the media, are not big fans of. The Acros unit uses a custom top cap that does blend in neatly with the top tube recess for a clean silhouette. But once the bars are turned, the knife edge like top cap sticks out and makes my knees and undercarriage nervous.
Very early full suspension bikes used linear sliding suspension elements (quite the mouthful). They were fraught with shock failures, something we might have too quickly forgotten about with the current prevalence of shock extenders. The switch to linkages was partly fuelled by this, along with advancements in and a better understanding of suspension systems.
Linkages, however, have a big conflict inside them. On the one hand they generally want to be small, light, stiff and easy to package in a bike. But at odds with this is that, generally, longer links give better suspension characteristics. Making the distance between the pivots points bigger tends to smooth out the suspension curves and give smooth changes that can translate to suspension predictability when you’re out on the trails.
But everything is cyclical, and so we’re back talking about linear sliding suspension elements. Something not completely foreign if you’ve followed Yeti’s history. But for ARC8 it gave many benefits for the XC race application.
The slider system could be very small, light, stiff and easy to package in the bike, while mimicking the effect of having a really long linkage. Infinitely long in fact. It also gave some really easy tuning possibilities in development - changing the angle of the sliders alters only the progression. Moving them up or down changes only the amount of travel. For ARC8 it houses Norglide bushings that slide on the polished and hard anodized rods, all sealed up with Swiss made SKF seals.
While the slider is the centrepiece of the bike, The Evolve is technically just a single pivot design, that main pivot defining a lot of the character of how the bike accelerates and decelerates. It relies on a flex pivot out near the dropouts, something now commonplace in short travel and lightweight bikes, but necessary to account for the movement of the seatstays relative to the chainstays.
The slider compresses a 210mm long shock that can use either a 50mm or 55mm stroke to deliver 100mm or 110mm of suspension.
It's also a low leverage ratio overall, coming from using a shock usually used to generate much more rear wheel travel. Starting at just 2.1, somewhere that most other bikes often finish, it falls to just under 1.9:1, making for around 10% progression. That low leverage ratio means much less air is needed to achieve the desired sag when compared to a more highly leveraged bike.
With the main pivot sitting a touch higher up than some other XC bikes, there's a decent dollop of both anti-squat and anti-rise in the Evolve, which goes towards combating the effects of load transfer under acceleration and braking. Anti-squat, in a 32/25 gear, starts around 115% and only drops as low as around 95% by the end of the 100mm travel. Anti-rise starts at just over 80% and drops to 60% by the end of travel.
Aggro Geometry & Modern Sizing
Originally three sizes were planned. But once the first riding sample in size M arrived, ARC8 found that riders ranging from 160cm to 180cm were fitting the bike. After some sleepless nights, a lot of chin scratching and measuring, they decided to take the bike to a renowned bike fitter and doctor of the Swiss Olympic team, Andreas Gösele, to get to the bottom of it. In the end, the S size was dropped in favour of only the M and L with their versatile and adjustable, with the different fork lengths, geometry's ability to fit a wider range of XC rider heights.
That M and L size having reach numbers of 477mm and 507mm respectively, that shorten by 12mm when running the bike with a full fat 120mm fork rather than the semi-skimmed 100mm. On paper that’s a big reach, and might bring some preconceptions before riding, but we’ll get to that later. Both sizes are designed around a shorter range of stem lengths than more traditional XC bikes – between 35mm and 70mm. But the stem length also ties into the head angle of the bike.
The steep head angle and longer stem of a traditional XC setup somewhat work with each other. The sometimes twitchy steering from the steep head angle can be controlled with a longer stem length. On the other hand, a slacker head angle can benefit from a shorter stem length to up the directness and speed of the steering. The added benefit being that with a slacker head angle the front wheel is much further from the rider and aids confidence when attacking on steeper descents. ARC8 went with the latter and with a 100mm fork the head angle sits at 66.1°. Put the 120m fork in and it slackens out to 65°. Something usually reserved for bikes with bigger travel numbers and much more of a focus on the downs.
In the middle the BB drops 43mm with the 100mm fork and 35mm with the 120mm fork. That should equate to BB heights of around 328mm and 336mm respectively, depending on tire choice.
Seat angles are 77.1° or 76° depending on the fork, which is a touch slacker than some of the big enduro rigs that the Evolve takes a lot of other geometry details from. But it’s certainly not slack when comparing to other XC bikes that can sometimes be close to 2.5° slacker.
Both sizes have a 430mm chainstay length out back, which goes against the current trends of growing chainstays, especially with such big reach numbers. ARC8 say they did this as they prioritise nimble and quick handling, especially in this short travel category.
Head tube lengths are short – 100mm for the M and 110 for the L. But with a slacker head angle comes a shorter stack height, allowing ARC8 to squeeze the 120mm fork in with a low stack that doesn’t need a wild stem to get into a really aggressive position if that’s your preference.
Build Options, Price & Availability
The Evolve is available in three full builds as well as the frame kit. Highlights include Bikeyoke’s Divine SL dropper post and Newmen wheels on all builds, as well as ARC8’s own component brand, Faserwerk, Baslerstab combo on all builds. The Evolve is available to purchase right away, with dealers already having some stock.
The XX1 build is 100mm travel front and back with remote lockout, while the XTR and XT builds use the 120mm fork and 110mm travel at the rear. Framesets come with 110mm travel.Evolve XX1
- RockShox SID SL Ultimate 100mm fork and SID Luxe Ultimate shock. SRAM XX1 AXS drivetrain. Magura MT8 SL brakes. Newmen Advanced SL X.A. wheels with Wolfpack Speed 2.4" tires. Faserwerk Baslerstab combo. Bikeyoke Divine SL dropper. Repente Quasar saddle. €9,999. 9.5kg.Evolve XTR
- Fox 34 SC Factory 120mm fork and Float DPS Factory shock. Shimano XTR drivetrain and brakes. Newmen Advanced SL X.A. wheels with Wolfpack Speed 2.4" tires. Faserwerk Baslerstab combo. Bikeyoke Divine SL dropper. Repente Quasar saddle. €8,999. 9.8kg.Evolve XT
- Fox 34 SC Performance 120mm fork and Float DPS Performance shock. Shimano XT drivetrain and brakes. Newmen Evolution A.30 wheels with Wolfpack Speed 2.4" tires. Faserwerk Baslerstab combo. Bikeyoke Divine SL dropper. Repente Quasar saddle. €5,999. 10.7kg.Evolve Frameset
- Fox Float DPS Performance shock. Across headset. ARC8 rear wheel axle. €3,299.
Back in February I managed to grab some hot laps on the Evolve FS at the Bike Connection Agency Winter event in Tuscany, Italy. For that particular day I also managed to line up half the test session on a race-ready Scott Spark RC before jumping across to the Evolve FS. Both bikes have XC racing firmly in their crosshairs yet go about it with drastically different strategies. And while a handful of runs is usually only enough to tickle the initial ride impressions, I wasn’t quite ready to have my socks blown off the way I did. ARC8 has created a monster of an XC bike.
While the on paper reach can bring some preconceptions about the ride feel, the low weight of the bike allows the bike to dance about with such ease and sprite. With such a low weight, the really long geometry is much easier to manage and manoeuvre. Spending most of my time riding downhill or enduro bikes, the position of the Evolve feels very familiar. Asked to shut my eyes and put my hands where I think they should be on the bars and I’d likely be within a mm of the ARC8. That familiar feel to bikes with more travel is no surprise when looking at the geometry, and probably helped a lot with feeling so at home so fast. But ARC8 was keen to point out that riders coming from long carrers racing XC, while apprehensive looking over the geometry, were won over quite quickly with the bike's handling and the benefits that they were getting from the really modern geometry. At the races, the bike has already claimed a top 30 position in the Elite Women's field at the recent Albstadt World Cup.
The bike and the slider suspension feel is very taut and direct, but not at all to the point that I had my fillings rattled out. You can feel that there’s not all that much travel, especially when jumping between bigger enduro bikes, but it handled the 110mm with brilliant composure and gives good suppleness to take the sting out of the trail and give nice traction while handling bigger trail features and rider inputs with buckets of support.
The mix of short travel combined with the really aggressive geometry creates a ride that is hard to put into words, in a good way. The bike’s shape eggs you on to push faster, to pull up off things that shouldn’t be pulled off and the tiny amounts of suspension does a fantastic job of keeping up with it. But when things get really spicy, and where it’s hard to substitute for more travel, the geometry lets you get away with murder. I think I was just as surprised as the guy in front, who had 60mm more travel, to be following him without much of a problem. The fact that he was on the wheel of Olly Wilkins might give an idea of the speed that this little machine can be capable of. After only a few laps I was a little taken aback by not only how comfy on the bike I was, but at just what it could do.
It was a great place to spend some time in the saddle, pushing hard on the pedals. The seated fit is comfortable and upright enough to never feel like you’re hanging over the back wheel. Which is good, as the front wheel is a lot further away than it was on the Spark. But there was no need to be doing big shifts in position to keep weight on the front wheel, even on steep and slippery climbs. And push on the pedal with any form of pressure and you certainly feel like it’s all going into propelling the bike forward. Much of this feel comes from the really supportive and direct feel of the suspension, which with its low leverage ratio and good dose of compression damping meant that I had no desire or need to use the shock’s lockout. One less thing to think about when you’re breathing out your arse and mashing the bar controls as you crest the climb. But then the XX1 bike does come with a remote lockout, which does make sense for proper XC racing.
As enduro bikes have progressed, their influence on the trail segment is clear to see, and something that we've all benefited from with just how capable the bikes are. And perhaps I wasn’t alone in wondering what a bike with even shorter travel would feel like with the same geometry. ARC8 have not only answered that with the Evolve FS, but also used some well-thought-out solutions and engineering to make a unique bike that may be more impressive than a lot of other XC and downcountry bikes on offer at the moment. And perhaps for a while to come.