Review: Atherton AM.150.1

For now, at least, the AM.150 is the only single-crown bike in Atherton's range, so they've designed it to cater to a relatively broad range of riding. I'm not going to keep you waiting - they've done a great job.

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Frame Details


While 3D printing seems to be everywhere these days, Atherton's application of the technology offers several benefits. Their additive manufacturing process (3D printing) means that the same machine can make lugs for any sized frame (not just the 22 "off-the-shelf" sizes but custom ones too) with only a change to the computer code it's fed.

Making a carbon frame the traditional way means investing in expensive moulds which are specific to each size. This limits the number of sizes a brand can produce and still make back the costs of molds (especially for smaller brands). It also makes it financially impossible to update the design regularly, which is something Atherton has taken full advantage of, even producing a new shorter frame for team rider Charlie Hatton in under a week between World Cup rounds.

The titanium lugs are made to order in a vast additive manufacturing machine at Atherton HQ in North Wales. This machine takes tiny titanium alloy particles in the 10-45um range and melts them together with four high-power lasers. It takes the AM machine 16 hours to build up the lugs for one bike out of about 3500 layers of melted titanium powder.


The lugs for one bike come out of the machine on a single plate, which is then heat-treated for strength. The lugs are removed, CNC machined for bearing, headset and bottom bracket fittings, and finished by hand.

The carbon tubes are cut to size (each size has unique tubing lengths) from three-metre sections. These are then glued into the lugs, which feature double lap shear joints. This means the titanium lug fits snugly around both the outside and inside of the tube; the glue is allowed to squeeze its way out as the tube is inserted, ensuring no air bubbles. The lugs are bevelled at their ends, which reduces the stress risers that would otherwise occur at the point where the tube enters the joint.

While the straight, round tubes may look simple compared to the curvy carbon frames we’re used to seeing, the idea is that the titanium lugs deal with the areas where stresses are concentrated and multi-directional, meaning straight tubes with constant wall-thickness are the right tool for the job in-between. While the tubes are made in New Zealand, they are built to Atherton's specs. Since the first AM.150 bikes we rode, Atherton have gone for lighter tubes on the seatstay and chainstay, giving a lighter and more flexible back end.




The AM.150 frame not only passes the EFBE Catagory 4 lab tests (for All Mountain and Enduro usage) but also the Catagory 5 (Downhill) test for strength and durability.

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Geometry & Sizing


Atherton's website allows you to plug in your height, arm span and inside leg measurements, from which an algorithm will spit out what Atherton deems to be your ideal geometry numbers. For my measurements (191, 195 and 93 cm, respectively) this custom geometry appears on the right of the above image. This put me in between the 500 and 510 mm stock sizes, but I decided to go with the 510, whose geometry is shown on the left.

I'm not going to go through the numbers of all 22 stock frame sizes, but you can plug in your own numbers here and compare all the sizes here. It's worth noting that there are three chainstay lengths across the size range. Sizes 410 to 440 get 433 mm chainstays; 450 to 480 get 438 mm chainstays, and 490 to 530 get 443 mm chainstays. The effective seat angles go from 76 degrees in the smallest to 79 degrees in the tallest sizes. Headtube lengths go from 100 mm to 125 mm. For some reach numbers, there are two options for the seat tube and head tube lengths; for example, there's the 500-Regular or 500-Tall.

Going back to the custom sizing, I asked if it's possible to go beyond the geometry numbers suggested by the algorithm, for example, to mix and match a longer chainstay on a shorter frame (or visa-versa). This is what Dan Brown at Atherton had to say: "We strongly feel that our recommendations on geo are the best riding bikes for the given rider. However, if someone is adamant they want to go longer or shorter on rear ends we understand that riding styles sometimes contribute to geometry. Over time we would like to take riding styles into consideration when recommending frames but this is a body of work we are still developing."

As always, I measured my test bike's geometry numbers myself, and most were within spec, or as close as I can measure. The one discrepancy is with the effective seat tube angle, which I measure at 76.5 degrees to the top of the seat post at my pedalling height. The 78-degree figure in the geo chart comes from the angle of a line drawn from the BB to where the seat post is level with the top of the head tube.

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Suspension Design


Atherton bikes use a revised version of the DW6 suspension design that we first saw from Robot Bike Co back in 2016. The DW6 name refers to the designer - Dave Weagle - and the fact that it's a six-bar design. That means there are six frame members: the mainframe, rocker link, seatstay, and chainstay, plus two short links connecting the chainstay to the mainframe. These links cause the chainstay to pivot about a point in space (the centre of curvature) which moves as the suspension cycles, which wouldn't be possible if it was fixed to the frame on a physical pivot. This has knock-on effects on the overall kinematic.




One obvious downside of this design is its complexity. Looking at the exploded diagrams, I counted eighteen frame bearings. I had a casual three-hour chat with Dave Weagle to understand the reason behind those extra links and pivots.


Essentially, he wanted to achieve similar performance to conventional four-bar DW link bikes (which use two short links and a triangulated swingarm, like you'd see on a Pivot, Ibis or an Iron Horse Sunday) but in a package that could be easily adapted to suit multiple frame geometries and chainstay lengths. The triangular swingarm of a DW4 design can't easily be adapted to custom geometries and the kinematics can't be so easily or independently tweaked either. At first glance, the DW6 looks more like a Horst-link than a DW link, and a Horst link would allow them to use the carbon tubes and 3D printed lugs needed for custom geometry, so I pressed Dave what specifically his DW link designs achieve that a Horst-link can't:


It's a similar story with anti-rise - the effect of the brake force on the suspension. The anti-rise levels are designed to be relatively high and consistent where it matters, helping the bike to resist dive without making the suspension harsher while braking.

Another important hallmark of Dave's designs, which he says hasn't changed much since the days of the Iron Horse Sunday, is the fact that the leverage ratio drops off quickly to start with, then levels off somewhat towards bottom-out. This is called a progressive-to-linear leverage curve, and it's something you'll see on a lot of bikes these days. Dave says he's been tweaking and experimenting with the leverage curve a lot over the years, including with the Athertons, but it's the same basic shape as it ever was.

The idea is to offer ample sensitivity at the start of the stroke, with enough support in the middle part of the travel without it being too firm towards bottom out. In terms of overall progression, it's nothing too wild. Interestingly, Dave mentioned that while a lot of pro racers think they need very progressive suspension designs, they often come round to a more modest amount of frame progression because if the leverage ratio drops too low, the shock has to move faster and it can struggle to flow enough oil at the speeds they are hitting things. Apparently, most of the Atherton DH team are now running a less progressive setup originally designed for Rachel.

As you may have guessed at this point, Dave and Atherton aren't keen to share specific numbers and charts, partly because they are part of their secret sauce and partly because they can be misinterpreted. Dave also warned me that off-the-shelf linkage modelling software can be inaccurate, particularly when it comes to more complex designs with short links.

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Specifications

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I set the fork to 98 psi, rebound a few clicks from fully open and compression varied depending on terrain, but generally close to open

I also ditched the 50 mm stem in favor of a 40 mm one and played around with bar height, settling on 30 mm of spacers under the 30 mm rise bar - kudos to Atherton for leaving some steerer tube to play with. Tire pressures were 22-23 psi (front) and 25-26 psi (rear). I also fitted some lighter tires (Maxxis Assegai and Dissector in their EXO casing) for a few rides.

Climbing

The Atherton is a thoroughly competent climber. The suspension is nice and steady under power. There's some movement at certain cadences, but I put this down to the lighter damping setup I used, and it never feels like there's much energy being wasted or excessive wallowing. The 76.5-degree effective seat angle (at my pedalling height) is comfortable for most climbs. When things got steep and technical, I'd prefer a degree or two added to the seat angle for a more aggressive position, but the suspension never slouches or collapses when the bike is pointed upwards so it's totally manageable.

I did wonder if the high anti-squat suspension would make it hang up when pedalling over bumps, but this doesn't seem to be an issue. The stock tires roll slow (for a trail bike), but with trail-casing tires fitted the Atherton is a very capable pedal-all-day kind of bike.

Descending


When it comes to describing how the AM.150 handles while descending, the word I keep coming back to is "solid".

Despite minimal chainstay protection, it's reassuringly quiet, which always helps instill a sense of calmness. The suspension is businesslike in the way it operates. Even with 30% sag and a volume spacer removed, there's loads of progression (I never felt it bottom-out) but at the same time, there's no sudden ramp-up of force making it feel like you've hit an invisible barrier before the end. Sensitivity near the start of the stroke is impressive, which is great for skimming across cambers or webs of roots without losing traction or momentum, but at the same time, there's plenty of support holding you up when pushing deeper into a corner. It's always measured with its use of travel, but it never feels harsh.

Much of the sense of composure comes from the suspension's built-in mechanical support (anti-squat and anti-rise) which stops it from slouching when you stamp on the pedals or pitching forwards when you jam on the brakes. The chassis feels stable and unfussy when things get hectic. This is partly why I preferred a less damped shock setup (especially on rebound) than recommended - you can run less damping for a more sensitive and lively feel without it becoming unsettled.


Even with my softer than recommended settings, it doesn't isolate you from the trail as much as some enduro bikes, especially when it comes to bigger hits, but the AM.150 is designed to be more of an all-rounder, and this is just a consequence of that support later in the travel which feels so good when pushing into corners and compressions.

The geometry is well-rounded, with no unusual quirks to get used to. Combined with the supportive and stable suspension, this makes for a composed and predictable ride in most terrain. At 65-degrees, the head angle is at the steeper end of the spectrum these days. When riding trails with little gradient and lots of tight bermed corners, jumps and rollers, this is no bad thing; it reduces the wheel flop and makes the steering quicker. With the rear suspension rewarding pumping and pedalling, this makes it feel nice and responsive. It's easy to muscle through tight turns and generate speed through them.

I briefly rode Gee Atherton's AM.150 at Dyfi bike park, which had the older tube set with a stiffer back end. Atherton say they updated the seatstay and chainstay since then, partly to add compliance on off-camber turns, although the bike I tested here still feels pretty stiff, which contributes to the solid and responsive feel when cornering hard.


When it came to the steeper trails in the Tweed Valley, the steering wasn't as predictable and steady as many of the slacker bikes these days. This is particularly true when there's a steep section with a step or trough into a corner. I definitely wouldn't describe it as twitchy, but not quite as steadfast in those situations as bikes that are a couple of degrees slacker. This is why I gravitated towards a setup with a softer shock, higher bar and shorter stem. The Fox 36 fork may not be as stout as the 38 mm chassis forks found on most enduro bikes these days either, and this may contribute to this steering sensation, but when I've tested the Fox 36 and Fox 38 back-to-back I found the handling differences in corners to be small. It's over large bumps and holes where the stiffer fork performs better.

The AM.150's supportive suspension and relatively steep head angle put it closer to the trail category than most thoroughbred enduro race bikes. This is easily forgotten given the downhill tires and the downhill pedigree of the siblings it's named after. But while there are enduro bikes that are more comfortable in the rough and more stable in the steepest chutes, the AM.150 holds its own compared to those bikes while feeling more at home on mellower and flatter terrain. It's a highly versatile bike.

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How Does it Compare?

With ten millimeters more travel at each end, a burlier fork and a slacker head angle, the Canyon Strive is billed as a thoroughbred enduro racer while the Atherton is perhaps more of an all-rounder. But in many ways, they have a surprisingly similar ride feel. They also have similar componentry and I've been riding both a lot lately, making a direct comparison easier.

Suspension-wise, both feel exceptionally stable under braking, with less of the pitching you get with some bikes, and none of the harshness you get with others. Both pedal well too, although the Atherton feels a bit more efficient under power (when compared to the Strive in its "shred" mode). Both have a progressive-to-linear leverage ratio and a Fox Float X2 shock, which means they are both very good in terms of the "touchdown feel" and suppleness over small stones and roots. With 10 mm more travel, it's no surprise that the Canyon is more forgiving and smoother when things get nasty, but then the Atherton is slightly more supportive through the turns.

The most notable difference is the head angle. The Strive is two degrees slacker, which means these bikes sit at opposite ends of the normal range for aggressive trail/enduro bikes these days. As a result, the Strive is noticeably more relaxed when tipping into steep catch berms and carving through rocky sections. On the other hand, the Atherton feels more manageable and at home on flatter, flowing trails (especially with faster-rolling tires fitted). It's horses for courses, but personally, I prefer a slacker head angle.

The Atherton's climbing performance slots in between the Strive's "shred" and "pedal" modes. Although the seat tube angle is similar on paper, the Strive sits a bit higher and feels more upright when in its "pedal" mode.

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Technical Report


Fox 36 Factory fork: The 36 is still a standout fork with excellent suppleness and support. Along with the head angle, the choice of the 36 over the 38 is suggestive of a trral bike rather than an enduro bike, but realistically the performance is near identical. The 38 only really starts to have an edge when you're battering through big rocks.

Continental Kryptotal DH tires: DH tires are at odds with the rounded nature of the bike, but they're standout performers in terms of traction, comfort and predictability. My views of them haven't changed much since my original review. They are heavier and slower than a trail tire, so arguably faster tires would suit the bike's intended use better, but nevertheless, they aren't a bad choice because the downhill performance is so good.

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