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.
Despite appearances, the AM.150's suspension has more in common with a DW-link (left) than a Horst-link (right).
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.