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Engineering Bell: Part II – The New Bell Zephyr

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In part one of Engineering Bell we met Ben Penner, Bell Helmets Sr. Product Development Manager, and got a little glimpse into his background and product design philosophy. In part two of this feature Ben takes us behind the scenes for an in-depth look at the development of what might be the most technically advanced helmet Bell has ever made, the new Zephyr.

RELATED: Read Part One of ‘Engineering Bell’
[PELOTON] The new Zephyr? What were your goals with this helmet? How is it different? We hear a lot of talk about dual-density helmets but the Zephyr is a whole other animal, correct?

[Ben Penner] The overarching goal was to make best all-around road race helmet we could. So when we thought about what people really wanted and needed in a road race helmet, our key priorities were ventilation (think about climbing Mount Ventoux under a blazing July sun) and fit (this is a helmet people are going to take on epic rides). Aerodynamics was a consideration too, but since we already make a really fast aero helmet with the Star Pro, our design requirement was that anything done for aerodynamics didn’t compromise ventilation or fit. A good example of this would be the lay flat webbing Triglides. We learned a lot about aerodynamics when we developed the Star Pro, one of them was that twisted webbing could cost you almost 10 watts at 50kph (that alone can be the difference between an aero helmet and non-aero helmet). However, safety is always the top priority for us, that is the primary purpose of every helmet we make.

The Zephyr's bi-furcated construction goes beyond simple dual density foam to mold two completely different pieces and then physically and chemically bond then.
The Zephyr’s bi-furcated construction goes beyond simple dual density foam to mold two completely different pieces and then physically and chemically bond then.

In terms of dual density, it is best to think of the properties of higher and lower density EPS. Dual density which consists of lower density EPS, which is lighter weight and easier to crush, and higher density EPS, which is heavier and harder to crush. This technology has been around in certain helmets for a while now. We employed it in a skate helmet years ago to increase the density to help support areas around vents, other people have utilized it to reduce the weight of a helmet by lowering the density at the bottom of the helmet below the test line. The bifurcated construction is a construction method that we’ve patented, and is essentially like building two separate helmets and then assembling them with both a mechanical and chemical bond. We have an outer helmet with a higher density EPS and multiple sheets of polycarbonate in-molded to it which function like a bug’s exoskeleton. Then there is an inner helmet with a lower density EPS which again has multiple sheets of polycarbonate in-molded to it. During our development impact testing we ran trials with a number of combinations of densities and polycarbonate shapes to optimize the impact performance per the certification and Bell’s own internal standards. It is the bifurcated construction that gives the engineering team a greater ability to optimize the helmet’s ability to manage energy compared to either a dual or single density helmet.

For example, with the bifurcated dual density construction of the Zephyr there are several clear benefits:

· We could increase both the number of polycarbonate sheets or shells as we call them, and have a lot more freedom of where to place them in the helmet. Instead of just on the outside of the helmet, I can layer them and place them in strategic locations. An analogy would be how a carbon fiber frame’s layup is optimized.

· Molding the helmet in two parts increases the amount of tooling pull directions we can use, so we have more flexibility to optimize the shape of the helmet.

· When you are molding EPS there are a lot of small steam vents in the tooling which are critical to producing a good consistent product. With traditional dual density your options for placement can be restricted by access to the steam vents. With a bifurcated construction, since we are molding the dual densities separately we have more freedom to put the lower density foam wherever we need it.

[P] What type of process do you start with? How does it proceed? Sketch pad, computer, clay, rapid prototyping, etc…?

[BP] We always start from a brainstorming process as to the market and general features that are needed in a new model, and once we know the general characteristics or features that are necessary in the helmet, we parallel track engineering and industrial design. The engineers will work on energy management strategies or new functional parts and provide input to the designers. The designers work on the aesthetics and fit of the helmet. It depends a bit on who the designer is on the project—every designer will have their own approach during the initial conceptual stages. It always starts with a sketch though and from there it goes one of two ways. Either straight to CAD (computer), or hand modeling. Hand modeling can start with ½ scale foam helmet “eggs” which the designer can quickly carve out a number of ideas. From there they move on to a full scale clay model of the helmet, since the helmets are symmetrical they usually just model one side of the helmet. When all the details are dialed in the clay model is scanned here and CAD of the entire helmet is made. From there we do a 3D Print of the CAD and so that we can check fit, see how it looks on people, etc. Along the way there are a lot of check-ins with the whole team including product marketing and graphics. Once we have final approval we go into a long process of tooling, a lot of internal impact testing, graphic development, and finally on to 3rd part laboratory certification. Finally, we do a pilot (trial) production run at the factory and then into mass production.

[P] How is the Zephyr’s Mips integration different than other helmets with the Mips sticker we see?

[BP] From a functional standpoint during a crash, it performs just like the other Mips you see. Where it is completely different is how well the helmet fits versus the other Mips helmets on the market. The integrated Mips LFL is made from a different material and manufacturing method (injection molded nylon) compared to the traditional MIPS (LFL vacuum formed polycarbonate). The result is that it conforms better to the shape of your head, and since it is part of the actual fit system it really disappears on your head. We have to invest a lot more up front in tooling, but the end result is a far more comfortable helmet that also fits better.
[P] The details of the helmet, the lay flat ear straps, the sweat drip tab up front, those impressed us so much. Really seems like it’s a very well thought out helmet. Can you tell me how those ideas came about?

Testing the Bell Zephyr on the climbs outside of Zurich. Image: Brian Vernor

[BP] It’s always a collaborative effort between product marketing, industrial design and engineering. We start with a pretty blank slate and consider things like who the end user is, generally what type of helmet it should be, and then just through a serious of ideation meetings, we think about what features would be important to the end user. For example, the sweat drip tab started as a discussion on how we were all annoyed with sweat dripping in our eyes while riding and that no one had really come up with a good solution. Then there was talk about trying to wick it away into a vent, sketches were made on the white board, but finally Hilgard (our director of product creation) had the idea of making it a tab and using gravity. He made some mockups and rode in them on some hot days in the summer and then it just evolved into what you see as the final product. It was the same for integrated Mips. It started out with us thinking about how to make Mips more comfortable and we talked about making the Mips LFL with injection molding. Then someone said, ‘Hey, if we are injection molding it we can put a gear rack on it and integrate it into the fit system.’

For me the thing that stands out about our team that developed this and every other helmet that we make, is that Bell has a dedicated team of engineers and designers whose sole focus is making bike helmets. We don’t make seats or bikes, we make bike helmets. There aren’t many other brands out there with more dedicated product development resources or with the amount of experience we have on our team. The key guys working on the Zephyr have been with the brand for 15+ years each. That’s a lot of bike helmet experience and knowledge going into the Zephyr.

To learn more about the Bell Zephyr, go to