BELL STAR SERIES - NEW MILLENNIUM HELMET TECHNOLOGY

 

SHELL CONSTRUCTION

Shell construction has very much been the place of focus over the last 50 years, as manufacturers tried to increase strength while decrease weight. Its purpose is to spread impact over a large area, preventing penetration of the helmet by any pointy objects. Also, it protects the inner liner from abrasion (grinding away), and helps the helmet to slide rather than twisting or rolling. The shell for a helmet can be made from many different materials, but are generally divided into 3 main types:

Polycarbonate
Polycarbonate (a type of plastic) is very commonly used in helmet manufacture, due to its low manufacture cost and high consistency in manufacture. Helmet shells can be repeatedly pumped out by a production line with no human work, and with reliable quality. However, polycarbonate flexes more than other shell materials, so to maintain the strength needed to pass safety tests, more material is needed. Therefore these helmets tend to be a little heavier than composite equivalents, and have fewer features. So they suit everyday street riding, rather than racetrack, and typically have a low price, even for quality brands. A typical good quality, reliable, safe helmet made from polycarbonate is the Bell Qualifier.

glass-helmets

A simpler fibreglass helmet shell (not a BELL brand). Notice the white strands of fibreglass are in random directions, which is the simplest method but not as strong.

Fibreglass

Fibreglass helmets have been around for a long time and are still the staple behind many helmet shells today. In fibreglass construction, extremely thin strands of glass are woven into a fabric or pressed together like a felt mat. The fibres bend due to their thin shape, but have a very high resistance against stretching. A ‘matrix’ material (such as epoxy resin) glues them together and holds them into the shape needed.
Bell produced the "Bell 500" open-face helmet back in 1954 which was a fibreglass shell, so this is not an entirely new material. However, times have moved on and even though similar glass fibre material is used, the method of construction has changed. Epoxy resin has been replaced by poly resins which are much lighter. In better-quality fibreglass helmets, short strands of glass, pressed together like felt, have been replaced in better helmets by long strands woven into a cloth fabric. This has allowed for less glass and less resin, so, lighter helmets and increased strength.

Due to the fibrous nature of the material, this also helps with energy dispersal, as each fibre is interlocked with another, therefore able to spread the impact area over a larger area. Often with a fibreglass helmet that has been damaged you will find signs on the opposite side to the impact in the form of small cracks. This is because the fibres have taken the energy around and away from the head and have reached the furthest point from impact and the stress can go nowhere else, causing it to crack. Additionally, you should be aware that it is possible for the strong fibres to break on impact, absorbing the blow, but without showing visible damage in the semi-flexible resin material that glues the fibres together. A helmet damaged repeatedly in this way can lose more than 70% of its shell strength. That’s one reason you shouldn’t re-use a helmet after a severe impact, and should replace it after several years of smaller knocks and bumps.
Due to the strength of the product, and being a common technology, you can find Fibreglass in most mid-level helmets. This usually means you have a thinner, lighter, stronger shell than a polycarbonate helmet. That's important for helmets like the Bell Bullitt where a thinner shell and EPS is critical for looks, but without compromising safety.

  Composites & Carbon Fibre

helmet-tri-composite-shell

This composite helmet shell is NOT a BELL. Notice the use of carbon (black) and aramid (yellow) fibres, and mostly glass fibre (white). The sand-coloured glue-like material holding the fibres in place is the resin matrix. After paint, you'd never know this contains less carbon and aramid, and more glass fibres.

Although fibreglass is one kind of composite material, when talking about helmets the word "composite" is often used differently. That is, it's used for helmets which "have no fibreglass", or "a mix of fibreglass and other fibres". Like fibreglass, the strength comes from thin fibres of high-tech materials that are very resistant to stretching, held in place by a ‘matrix’ material. These types of material feature in the new BELL STAR, BELL RACE STAR, and BELL PRO STAR.

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BELL's 3k carbon shell on BELL Race Star, with clear coating, where you can see the outer shell is all carbon fibre in a neat weave arrangement.

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On this Bell Star you can see that the Bell "Tri-Matrix" shell has much more carbon and aramid than the other brands' composite shell.

These materials can be found in most of the top end helmets; in Bell’s case they use the term “Tri-Matrix” for their mixed composite shells as used in the BELL STAR. The exact make-up of a composite shell is always a guarded secret by manufacturers, but we know the main components: an aramid fibre (such as Kevlar), carbon fibre, and glass fibre, all held together with a poly or resin. They offer the same benefits of a fibreglass helmet but improved weight saving, and in some cases impact strength.


Carbon Fibre is used to reduce the weight of the helmet, as it provides an extremely high stiffness (stretch resistance) compared to its weight, even more than glass fibre. It is unfortunately a difficult material to work with, and costs more than glass fibres; as such a similar helmet design in a glass or mixed-composite construction will be substantially lower cost than one which is mostly carbon fibre. However, depending on the construction method used, weight gains can sometimes be minimal as most composites are already a light material; the heaviest part is the EPS liner and the matrix/resin material holding the fibres in the shell. Lots of carbon is generally only used on premium race helmets, due to high production costs and small weight gains, such as the quality all-carbon outer on the BELL RACE STAR. Bell has taken this to the edge in their new Pro Star. Although Race Star and Pro Star are carbon fibre, the BELL PRO STAR has the latest in carbon fibre technology from TeXtreme...

 

textreme-web

Raw TeXtreme fabric showing its neat, flat, well-arranged weave

TeXtreme carbon material is used in the aerospace industry, as well as Formula 1 racing, and is a super-light-weight carbon fibre. It is even lighter than the normal carbon fibre used in the Race Star helmet. This now represents the pinnacle in helmet construction materials. It uses extremely fine fibres in stronger, broader tape-like ribbons, woven in a chequer pattern which keeps the fibres more aligned. This gives benefits over typical woven carbon fabric due to lower weight and less matrix material used, and higher strength.

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BELL Pro Star with TeXtreme carbon shell. You can see the larger, smoother weave pattern.

WHY DOES TEXTREME WORK?

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textreme-fabric-layup

TeXtreme has a broad weave which is stronger, thinner, and lighter, than regular weave patterns

IMPACT ABSORBING LINERS

Shell development has certainly been where manufacturers have concentrated a lot of their efforts in trying to reduce weight and increase strength. However the internal materials have also changed over time. This is another place that Bell has devoted time and effort into the new range of helmets.
Here, we will break down the internals of the helmet to show you the new technology.

EPS/Expanded Polystyrene foam
EPS, like fibreglass, has been around since the early days of helmet usage. EPS has improved over time, and it is extremely good at softening sudden blows, as long as the blow is spread over a wide surface area by the helmet shell. EPS is great for higher speed absorptions and will dampen the effects best of a higher speed impact. Some manufacturers now use multi-density EPS (a mix of softer and harder foams) to improve its effect under different loads, such as low-speed and high-speed impact. EPS liners make up the most important part of helmets, which shows how well this material suits the task.

MIPS/Multi-Directional Impact Protection System
MIPS is a new deal in the motorbike world, however it has been around the pushbike world for a few years now. It is used in conjunction with EPS-lined helmets. So what exactly is it? In short it is a piece within the helmet that allows the helmet to ‘slip’ a little (rotate around your head a tiny amount) in an impact. Why is this so important? Bell looked extensively at current test methods and head trauma. They found that some unseen damage caused to the brain in an accident were due to a cause that had been overlooked by manufacturers – sudden rotation of the head. Furthermore, all helmet tests were based on the helmet hitting directly on, without any rotational or sliding movement.

Tests are useful, but we ride in the real world. Multiple forces are put on the head and brain during an accident, even at slow speeds. This meant the helmets we not being tested for the same issues they would face in a real life scenario. So Bell turned to the people at MIPS, who had been studying this for years.

The ‘slip’ mimics the fluid that is naturally around your brain, that is your own inbuilt mechanism to protect it. By mimicking this, and allowing the MIPS liner to slip a tiny amount inside the helmet, it slows down the rotational forces that are being put on the head and brain. That reduces the stress and damage to the brain.
So MIPS is an addition to a normal style helmet, that takes the next step in safety. As a bonus, it is a smart simple design which doesn’t break the bank.

BELL “Flex”

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FLEX multi-layer helmet interior

“Flex” is the new kid on the block, and BELL the only ones with this technology. “Flex” is a total rethink of what materials can be used as energy absorption layers, to improve the result.


“Flex” consists of 4 main features, including a 3-layered liner for impact absorption which is the first of its kind. Each material is designed to do a different job. Bell looked at previous helmets and found that the EPS liner has change little for over 50 years. In that time, many new materials have come along, yet few were used in a helmet. This is how they came to use these.

1. EPO/Expanded Polyolefin: This material was added for its fantastic slower speed impact absorption and was added for slower speed impacts. When looking at a “Flex” helmet, this is the red material you can see.


2. EPP/Expanded Polyproplyene: This was added for mid-speed impacts; it was found to be stiffer than EPO, yet softer than EPS. It was perfect for those in-between impacts, working in conjunction with EPO.


3. EPS/Expanded Polystyrene: Yes, after all the testing Bell found that EPS was still the best for high speed impacts. The old saying goes, if it ain’t broke, don’t fix it. Bell used EPS again, in conjunction with the EPO and EPP, to create a 3-layered-liner like no other.


4. Design feature: segmented inner layers (EPO & EPP) This allows the inner layers to have a small amount of give. The inner liners to flex against each other, allowing for a better fit and will customize the fit to you. This feature of the liner uses learnings from MIPS technology. Although not MIPS itself, Bell has designed the "Flex" liner to act in a similar way, controlling rotational energy and allowing one liner to slip slightly inside the helmet during a crash.
All these features are why the “Flex” liner used in the Race Star, Pro Star, and Moto-9 Flex, stands as unique and the most innovative impact liner on the market.

Resources: Peter Stevens

Check out all Bell helmets here

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