Design of the Arantix Mountain Bike

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As most regular readers know, I am an industrial designer, but I do not work in the bicycle industry. As much as I enjoy writing about bikes a couple hours a week, my real job obviously has to take precedence over the blog, and any other bike related reading, when I get really busy. For the last week and a half, I was at a show where some of my new designs were released . Everything went well, but my schedule was extremely hectic to say the least. I was working long days and could barely keep up with my work email in my “spare” time, so I didn’t have time to check my blog or read any others. This morning, I checked the stats just to see if anyone was still reading Bicycle Design. Not only did the number of daily hits remain constant while I was away; I was surprised to see that the number of subscribers to the feedburner feed climbed firmly into 4-digit territory (1181 as of right now). Wow, I should stop writing more often. Seriously though, I appreciate the fact that so many of you read this blog on a regular basis and I hope you will continue to do so. The way Bicycle Design is growing each week; I won’t be surprised if the page hit counter hits the 1 million mark some time this year. I am constantly amazed by the blog’s growth, so I want to say again that I appreciate all of you who read the blog and comment regularly. Thanks.

As you can imagine, I am too busy now that I am back in my office to come up with any new content. Luckily, I have what I think is an interesting post from a guest contributor to share with you today. Tyler Evans is the Bicycle Program Manager at Delta 7 Sports in Payson, Utah. As an engineering student at Brigham Young several years ago, he designed an isotruss bike that has received a lot of press. The Arantix bike was shown at Interbike last year and received a good bit of attention on blogs and websites (see posts here, here, here, here, here, and here to point out just a few).

As I just pointed out, a lot of information about the Arantix bike is available on the web, but I asked Tyler if he could explain to Bicycle Design readers a little more about the development of the design and how it came to be. In addition to writing about the design history, Tyler included a bit of an explanation of the technology itself. What follows is Tyler’s essay, in its entirety. I am sure he can answer any questions you might have about the design, so feel free to leave a comment. Oh yeah, before I forget, thanks again for the submission Tyler.

A brief history of the design of the Arantix Mountain Bike by Delta 7 Sports

The Arantix Mountain Bike by Delta 7 Sports is a high performance XC racing mountain bike that is designed around a revolutionary technology called IsoTruss™. The story of how the Arantix was born has to begin with how the IsoTruss™ technology was born.

IsoTruss™ technology is the combination of two light-weight, high-strength technologies, one is structural, the other is material:

First is the light-weight structural technology of trusses. Truss technology has been around for quite a while and is a time-tested method for transferring high loads through very lightweight structures. Everywhere you look you can see trusses carrying very heavy loads, from large crane masts, to bridges, to roof supports, to airplane frames, to skyscrapers. Trusses have a very high strength-to-weight ratio and stiffness-to-weight ratio. In fact, a traditional double diamond bicycle frame itself is just another kind of specialty truss, which is why it has remained virtually unchanged through the years, all across the cycling industry as the most efficient shape for a bicycle in terms of strength-to-weight.

Second is the light-weight material technology of high-modulus carbon fiber composites. While carbon fiber is a relatively young material technology, it is completely mainstream in the cycling world. Carbon is such a stable atom with such a strong molecular bond that it can be found at the center of almost every highly-evolved molecule in nature. In its purified form, carbon fiber has one of the highest strength-to-weight ratios of any material and it can be combined with a wide variety of resins or epoxies in order to “tune” the characteristics for any specific application.

The fact that carbon fiber starts out as a completely pliable fiber or fabric and then hardens into whatever shape it has been formed makes it ideal for creating exotic shapes and curves. The possibilities for smooth flowing surfaces and shapes are literally endless. For that reason, many manufacturers have not felt a need to think outside the realm of “continuous surface” molded design.

IsoTruss™ takes carbon fiber composites technology in a totally different direction. It winds the carbon fibers into very efficient open-lattice trusses that are able to support themselves against very high bending, torsional, compression, and buckling loads, without using as much material as other composite structures. The very unique IsoTruss™ shape with its regular peaks and valleys is optimized to keep all of the primary load bearing intersections at their very strongest.

Many bicycle designers have wanted to use larger diameter tubing in their bicycle designs because larger diameter tubes are better at resisting bending. But there is a limit to how large a “continuous surface” cylinder can be on a bicycle because as it gets larger in diameter the wall thickness must decrease in order to keep the weight equal and then the tube is susceptible to local buckling (like kinking a soda can). But a truss design allows the bicycle frame designer to have it both ways. The IsoTruss™ can have load bearing members spread far apart from each other like an I-Beam, but the thick support lattice members protect it from local buckling.

The IsoTruss™ technology was originally developed at Brigham Young University under the direction of co-inventor Dr. David W. Jensen. For a number of years their research focused on very large diameter applications like power poles, cell phone towers, radar antennas, replacing re-bar inside concrete pillars, airplane wings etc. They were always looking for new applications and load scenarios with which to demonstrate the advantages of a composite open-lattice truss. The research team was looking for any application that required high strength, high stiffness, and low weight. Building a bicycle out of IsoTruss™ seemed like a good fit for the researchers because it was a product that gets people excited, it is a competitive industry that has a “cutting edge” image, and it presented a whole new set of challenges for the IsoTruss™ that had not been previously explored. The bicycle project pushed the envelope for small diameter manufacturing techniques, component attachment and connection issues, and performance tuning. In all, the BYU research team made four bicycle frames. Each one significantly more advanced than its predecessor. Some of the early frames were focused more on the IsoTruss™ members than the complete bike, they were intended to prove a concept more than create a bike, but each one came closer and closer to a bicycle frame that met all of the design criteria.

The 3rd IsoTruss™ bike frame caught the attention of a senior engineer at Specialized and he suggested that the bike frame needed some good lugs in order to be more credible so he donated two pairs of titanium lugs that were left over from an R&D project that never made it to market. With the new titanium lugs and a lot of lessons learned along the way, the BYU research team set out to build one last concept bike. The fourth IsoTruss™ bike is the one that people usually have heard about because it was taken down to Interbike and captured by quite a few cameras outside the show.

A few years later a group of entrepreneurs with backgrounds in composites fabrication and aerospace industries purchased the worldwide rights to IsoTruss™ technology from Brigham Young University. The company’s name is Advanced Composite Solutions. Their plan was to develop the manufacturing process further and create a fully automated IsoTruss™ braiding machines. They will also sublicense the rights to IsoTruss technology and spin-off a series of IsoTruss companies for each broad category of applications. Rather than wait for the machine to finish development, Advanced Composite Solutions decided to begin creating subsidiary companies for applications that can still be viable using hand-built IsoTrusses™. Delta 7 Sports is the first company created by Advanced Composite Solutions and their focus is on all bicycle applications for IsoTruss™ technology.

Delta 7 Sports set out to create a race-quality bicycle that uses IsoTruss™ technology. The name Arantix was chosen for the project. It was derived from the scientific name for “Weaver Spider” which is Arantia and the latin word for “weaver woman” which is Textrix. The Delta 7 Sports team had a relatively short development schedule in order to create the bike in time for the 2007 Interbike show, so they decided to scrap the idea of using custom welded titanium lugs and go instead with a more advanced full-carbon molded lug set. The team partnered with ClosedMold Composites in Salt Lake City, Utah to create the lugs. ClosedMold’s founder, Ron Nelson, had previously been contracted by TREK to develop their successful OCLV lug technology, so they were already intimately familiar with what it takes to make carbon fiber lugs for bicycle loads and stresses. The Delta 7 Sports team knew that they could build on the previous knowledge gained by the BYU bicycle research in some ways, but in many other ways, they would have to start from scratch. Changes would include a totally updated geometry, updated connection points, new tube diameters, a change from rim brakes to disc brakes, and a new tooling concept for building the IsoTrusses™.

The completed Arantix frame weighs less than 2.75 lbs. It was unveiled at Interbike to very large crowds of people and wide spectrum of opinions. Most people are very impressed, some are skeptical. Delta 7 Sports is planning to have bikes at the Outdoor Demo in 2008 so that industry folks can ride it for themselves and see just how light and strong it is and just how well it handles.

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14 Comments

  1. Fritz January 18, 2008 at 6:34 pm -  Reply

    I didn’t have a chance to ride it, but I picked up the frame and was astounded how light it felt.

    Tyler also told me they’re developing a road version of the isotruss frame. I don’t know if the isotruss structure would violate the UCI rules that a bicycle be constructed of “tubular elements”, though I’m sure it would be a “technical innovation” that must be submitted to the UCI for their authorization.

    Are those bikes where the downtube is replaced with a cable UCI legal?

  2. Anonymous January 19, 2008 at 2:12 am -  Reply

    I’ve seen this bike go around the Internet several times already and every time it shows up somewhere the first comment is “what about mud?”

    How do you keep mud out of the truss?

  3. bikesgonewild January 19, 2008 at 5:36 pm -  Reply

    …bingo…

  4. Anonymous January 19, 2008 at 7:28 pm -  Reply

    1. Ugly. You know it, I know it.
    2. Its not any lighter than current high end carbon frames!
    3. Road version? The aerodynmic properties would be terrible.

    Theyve got a long way to go…Its nice to see a new frame technology…but if they cant step it up it will be gone and forgotten in a year.

  5. Ron January 19, 2008 at 11:21 pm -  Reply

    I have read about these in many places. While its a great research project for a university, I wonder how marketable this is?

    The essay isn’t technical in any nature. I was expecting some design and testing numbers, and how they manufactured something like this. The tooling and production costs must be huge.

    Like all other super exotic frames that come out of the industry once in a while, this piece might be doomed to hang on a select few people’s walls as well.

  6. Ron January 21, 2008 at 6:17 pm -  Reply

    James,

    The fabrication process for composite isotruss structures, research headed by David Jenson at UT was one of the 25 semifinalists in the 2007 Modern Marvels Invent Now Challenge. I thought you may like to know.

  7. Eloy January 24, 2008 at 3:59 pm -  Reply

    What anonymous said…

    It is a mountain bike, how do you get the dirt and mud out of it?

    Even on a road, cleaning it would be, well, messy.

    This is a failure of design.

    btw, Fritz, those cable bike are not UCI legal.

  8. jimmythefly January 28, 2008 at 6:20 pm -  Reply

    Somewhere they mention that a custom lizardskins cover set comes with the bike, which answers the mud question. Personally I’d go for saran-wrap, so I could still gaze lovingly at the truss structure as I rode along.

  9. bikesgonewild February 9, 2008 at 4:19 am -  Reply

    …jimmythefly…saran wrap, love it…

  10. ER Dog February 28, 2008 at 12:31 am -  Reply

    anonymous said…
    How do you keep mud out of the truss?

    I’ve just raced the Arantix at the Kona 24 hours in the Pueblo (Tuscon).
    The first lap (after 1 inch of snow fell over night!) was with some seriously muddy spots. Some mud got into the bottom of the down tube but had fallen out by the time I was done with the lap. On my full tubed bikes the mud usually caked all along the down tube which did not occur on the Aranix. Mud collection was a non-issue.

  11. Anonymous April 5, 2008 at 10:01 pm -  Reply

    I’d love to attach a couple of carbon-fibre lattice wings and take it for a fly

  12. Anonymous May 1, 2008 at 11:47 pm -  Reply

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  13. Sifua April 19, 2009 at 6:14 pm -  Reply

    This bike is amazing!
    I had a chance to try it out at the 2009 Sea Otter, and i feel in love with it.
    It is the lightest bike out there. You can easily pick it up and run with it, with no pain the the arms.
    The bike’s design it is eye catching. For example, when i was riding it so many people looked at me. After i was walking around and a person came up to me and asked me where i got the bike, becvause it looked amazing.
    If you can try out the bike, you will fall in love with it.
    It is seriously the best racing machine out there

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