The new Atherton DH bike with its mix of carbon and titanium is definitely divisive among those who see it. Whether you think it looks wrong or right, the technology behind it is pushing brand new techniques and processes into the industry. The Atherton's are definitely trying to produce something that is very different, so to get a better understanding of how and why these bikes are made, we chatted to three of the engineers: Ben Farmer, Rob Gow, and Ed Haythornthwaite.
What is the process from design to complete bike?Ben:
First you go onto our website and enter your height, arm span, and inside leg length. Our program then shows a suggested ideal geometry. If this fits what the rider wants, then the data from the website feeds directly into the CAD system.Rob:
Basically, all the different lugs are controlled by a formula, so when you put in height, inside leg and arm span, that automatically alters all the angles. If we were to be manually changing this all the time, it would take weeks to design each bike. So, that sort of intelligence is built into the model. Once we have the riders' unique data and their desired designs, we send those to Renishaw. (Renishaw is a manufacturing company based in Gloucestershire, United Kingdom. They produce the machinery that can print the titanium lugs for Atherton bikes.)Rob:
It then takes about 16 hours to produce one bike's worth of custom lugs, based on their unique requirements. Ben:
The Renishaw machine builds the lugs using titanium powder. There is a four laser setup up in there, they all shine down onto a metal plate that sits inside and is spread with a six-micrometer thick layer of titanium powder. The lug is then built layer by layer until the design is complete. This is usually made from 3,500 layers. They are all checked dimensionally - they are real experts in dimensional checking at Renishaw. The lugs arrive to us attached to a one-foot-square plate and they all sit there until they are then cut off. There is then some final machining to be done, like bearing faces for the headset and the bottom bracket.
We then bring in carbon tubes which have been designed to our specifications. Each tube is different, with a separate layup. We then cut the tubes to length and they go into a set of jigs to ensure accurate construction. Next, we inject adhesive into the cavity in the lugs, called a double-lap shear joint. There are three reasons why this style of joint is particularly strong. Firstly, with a single-lap shear joint, when you load that and pull it to tension, it can twist, With a double-lap shear joint, when you pull it to tension, it doesn't twist, It produces what is called "shear forces."
If you ever put a bit of tape on a table and try and pull it off, how would you do it? You would peel it off. What you wouldn't do is try and pull it off, because it would be really hard to get off. That is basically how these work. So, it is very strong. The second thing is when you inject the adhesive, you can witness the adhesive being injected around the circumference of the joints, so you have complete confidence that the adhesive is in the joint. If you haven’t got adhesive in the joint, then you won't have a strong joint. The third reason is that, essentially, these things assemble themselves. You have the jig there to ensure precise positioning, but once the adhesive is in the joint the lugs and the carbon tubes slide together, it's just a case of making sure it is accurate and fully in the joint. It's very easy to assemble.
We then cure the bike at room temperature. This means we are not heating or cooling, so there is no expansion and contraction during the process. If we have it at room temperature, it is basically at the temperature where the bike will be used. In total, it takes at most two weeks to have a fully complete bike, from changing something in the computer to having it being ridden by one of our riders.
What was the idea behind choosing the combination of titanium and carbon for the frame?Ben:
What we are doing is combining the incredibly high specific strength of titanium with the high specific stiffness carbon tubing. All that comes together in a way that is unlike a carbon fiber frame. We design the lugs with a technique called "topology optimization," Which means we define the design space on the computer and then apply the boundary conditions that exist around it like: I need to have a bearing pickup here or; I need to keep the mud out of here, so it needs to be closed. Whatever it is, the computer figures out the best way to accurately use the material so it is not even 1% overused in that area. Actually, a lot of that subtlety gets missed because it is a mountain bike. Also, within the lugs is a variable wall thickness, basically it makes the use of material perfect and all of the parts.
The chainstay yoke offers the best example of this practice, the way this has been designed is to ensure mud falls off of it and to fully optimise the structural integrity of the component. So what we end up with it something with a very high specific strength. All that means is strength per specific weight. Titanium is the highest specific strength metal, for a given strength you have the lightest output. We have very high specific strength metal where the shapes are complex and the loads are complex. Loads come from all sorts of different directions and you have a vehicle with a really weird setup. You have a rider, with not much power, and the rider's main center of mass and gravity is all over the place.
Loads can come from all different directions, so you have a complicated set of things going on. With metals, they are suited to situations where both the shapes and loads are complex because their properties are the same in all directions. Once you move away from those areas of complexities where the loads get resolved, and more simple we use carbon fibre tubing.
Each lug has an incredible level of detail and design work
Carbon fiber does not work well in applications where shapes are complex, because you can't get all the fibers moving in the right directions. They don't work well when the loads are complex, because it is only extremely strong in one direction. So, with our design of using two different materials, what we end up with is something where we have the right strength in areas where we need it and we have some degree of compliance in areas where we want it, and we have stiffness in the other areas we want it.
You end up with a bike that has a very stiff suspension platform but offers some level of compliance. It works really well with the DW6 suspension platform to give impressive levels of grip. So working with Rach, Gee and Dan, they have been providing us feedback on that combination of stiffness versus compliance. We have then been playing around with the layups of the carbon tubing to build a platform which, for many riders, is more than proficient in terms of stiffness. But for the Athertons, because of what they do, they can benefit from the added stiffness. That's been the whole winter's work, really. Rob:
Because we don’t use molds, we can quickly throw in new parts and play about with thicknesses and stiffness on CAD, change parameters, test it the next week, and you have the feedback. That development cycle means we can do in a month what another company might take six months to achieve.
Why did you go with Dave Weagle's DW6 suspension platform?Ed:
The main thing with that is, with feedback, it enables us to get the characteristics they want. The DW6 is one of the few options where you can isolate each of the key characteristics like pedaling, braking, leverage ratios and progression without them compromising each other. Normally, when you adjust one, it has a knock on effect on the other. Literally, they can isolate each aspect - say if they want it to give a little bit more in the mid-stroke or something like that. You don't then mess up the pedaling or the braking,
DW6 just offers huge flexibility, which has already been demonstrated by the tweaks we have done so far. We can do that without a knock-on effect elsewhere. Just works bloody well basically. They can't believe the grip it gives in particularity. When we were originally developing it, they were certainly looking for an advantage on flat corners and off camber, and it really offers that by having that extra confidence in grip. Gee has never ridden anything like it. We are also currently the only ones using it.Ben:
Another reason we use it is because it is very well suited to how we make these frames. Basically, it concentrates a lot of mechanics around the bottom bracket, which means it works well in terms of not having lots of breaks and joints in the carbon tubing. It also just so happens that when we set this up, the rocker pivot is where we need to kink the seat tube, it was all designed in unison. We needed to put a split in the seat tube and that is where we put the suspension. It was conceived as a whole platform that was tunable for the future. We needed it to work with how we were building the bike,
Dave Weagle was driving our developments. He came back with a bunch of different concepts and DW6 was the standout, as it fitted with our construction methods and designs - and it played well with our idea of customization and fine tuning things.
Could you change the riders' frames between races to adjust to tracks?Ed:
That's more of a question for Gee and Rach. It's more about getting the bike spot on for them and not the track. Once they have something spot on, they don’t like changing too much throughout the season. Should you actually change a bike for different tracks? The majority of the time, no. Once they have that bike setup dialed, you don't want to change anything major. Most of the development work we are doing now is to get the bike dialed. They may tweak very slightly, but nothing major.
What have you changed on the bike so far?Rob:
All the bikes so far have had slight tweaks, as they have tried to cram in as much testing as they can. We give feedback to Dave Weagle on DW6 that we have got from the riders and he will do some subtle tweaks. We also take feedback from Pete, the Atherton's race mechanic, like this bolt is hard to get to or it would be easier if this was here. The next prototype will then have all these features. You can really accelerate the development process and be really active with the constant stream of feedback.
How many prototypes have you made?Ben:
Nine so far, including the trail bike. We started the process in the first weeks of January and we should be up to 20 machines by the first race. At this point, it is been all tiny changes and most people couldn't tell the difference between each bike. The main thing is delivering each rider a custom bike, that they can push it, and be happy about them. Most of the work now is getting the sizing dialed for each rider's custom bike.
• Interview: Rachel, Gee & Dan Atherton Chat Business, Bikes & the Upcoming Season
• Bike Check: Dan Atherton's Prototype 29er DH Bike