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Reinventing Round

Innovate or Die

This a tale of two teams and two visions that created the most technically advanced bike Specialized has ever made. This bike will change the way we make bikes forever, and it carries its innovations in a deceptively classic package, built from a simple goal — create the ride of your life.

Three years ago, as our road product team at our Morgan Hill, CA, Innovation Center focused on more integration in the name of aerodynamics, squeezing out every watt per kilo and reducing every gram of drag, they began to dream of a new way. Is there a space for a classic bike with refined lines, simple cable routing, a seat collar, traditional stem, and threaded bottom bracket, all built around a frame with a singular focus on transcendent ride quality?

Meanwhile, in Specialized Freiburg, our carbon gurus had a “eureka” moment — a new theory for how forces moved through a frame. This theory proposed that shape was by far the most important variable — a more potent force for delivering ride quality than previously imagined. The team knew turning this theory into practice would require the most challenging and extensive simulation project in our history. Was there a project that could serve as a foundation for this work?

The answer to the two questions is the same, the Aethos. With the Tarmac SL7 — a race bike for every type of parcours, serving every racer’s needs — there was an opportunity to deliver a bike entirely dedicated to ride quality.

Aethos was born in the Freiburg test lab. Peter Denk, Aethos Engineering Lead, meditated on a frame in the pedal rig, watching the carbon flex and breathe under load. He watched as each fiber picked up the load and distributed it to the next. A concept, a notion, began to surface.

"“We think we know how forces flow through a frame, but after staring at it I thought, ‘Hmm…’ The whole industry thinks we need a big fat downtube that holds the BB. We think we know the proportions. But seeing how it flexed, I thought, ‘Maybe something else is going on?’”"

Determining exactly what was going on would take the largest simulation project Specialized has ever conducted. The team created over 100,000 virtual frames across the spectrum of design. On this virtual test rig, we tested for BB stiffness, front end stiffness, and overall stiffness — three key measurements that allow us to predict how a frame will ride. The data derived from this testing was so massive, the only way to process it was on supercomputers. Of course, the computers don’t tell you which of the 100,000 frames is best, they only deliver a landslide of data.

“We basically had a big cloud of results,” Peter said. “This frame was a little better on BB stiffness, this one a little better on front end, this one on a bit lighter. It was a nightmare.”
— Peter Denk, Aethos Engineering Lead

We experimented with ways to filter this data and make sense of it, landing on a system that discovered trends within the data. Tracing these trends with custom software, we were able to discover what single combination delivered the best overall frame performance.

"“The virtual frame was so strong and so lightweight that we thought, ‘If we build that out of carbon fiber, it’ll be crazy!’ But the biggest result was that by following these shapes, we eliminated all of the stiffness layers. We saved 150 grams of composite weight.”"

— Peter Denk

When we built the first raw frame it was only 545 grams. It performed so well in the test jig it required just 10 grams more to be test ride ready. At this point, the team knew they had discovered something monumental. Peter’s hunch was right. Conventional thinking about frame shapes was wrong.

Aethos’ deceptively simple shape delivers stiffness more efficiently than any frame before. Small diameter tubes at the bottom bracket and seat cluster are best, but we also needed a large diameter top tube and down tube to mate to the larger head tube. How the top tube and down tube taper to the bottom bracket and seat cluster is equally important.

The shape of these junctions has a massive effect on stiffness and stability under load. The subtlest change in curvature creates massive performance differences. Surprisingly, what is less important than previously thought is a big down tube mating to a big bottom bracket.

The Aethos isn’t light because we reduced wall thickness, it’s light because the tube shape carries the load and allowed for the removal of all stiffness layers. The frame deflects smoothly, beautifully under load, passing every test with ease. But these shapes deliver more than reduced weight. The stability, predictability, and durability translate to beautiful balance on the road.

"“As a rider you have a perfect feeling of what’s going on; it carves through corners; it gives you a lot of confidence. You feel more planted with better feel for what your tire is doing on the tarmac; it gives you the feeling, ‘Okay, I’ll go faster!’”"

The final result is the answer to our questions — a classic bike with clean, beautiful lines that happens to be the lightest production disc brake frame ever made. It’s a frame that’s not light because we chased a number, but because we reinvented how carbon bikes are made. And we did it all for the rider, in pursuit of the greatest ride quality on the road.