helmet design

8/7/2019 helmet design

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HISTORY AND STEP WISE IMPROVISATION IN D MATERIAL

In the beginning, there were injuries. From cycling's earliest days there were head injuries. As

more roads were paved it is likely that the head injuries increased, since macadam and asphalt

are completely unforgiving as crash surfaces. In the 1880's high-wheel users in clubs saw that

head injuries were a problem and began using pith helmets. Pith is a crushable material, andwas likely the best material available at the time. Although it would probably break up on

impact, there were few cars on the roads, so riders needed protection only against a single

impact.

Around the turn of the century racing cyclists began using "helmets" made of strips

of leather-covered padding, initially with a ring of leather around the head and a

wool ring above that. Then the style evolved and the ring of leather around the

head was supplemented by strips of leather arranged longitudinally on the head.

When I started racing in the 70's we called them "hairnets" and the nicest ones

were made in Italy of beautiful soft leather.

By then the interior of the strip was a foam, but it wasn't very protective. They also rottedfrom sweat. I asked the more experienced racers if the hairnet we were required to use in

races was protective, and they said "they don't help at all in the initial impact, but they keepyour ears from being ground off while you're sliding over the pavement." Years later lab

testing showed that their assessment from field experience was exactly correct.

By the early 1970's club and racing cyclists with shared experience could see that

the injuries that were the worst and the major cause of death were head injuries.

We could also see that a helmet could do a lot of good. Some riders just ignored


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that, as they do today. Others began using hockey helmets. Still others turned to the

plethora of headgear on the market, including "bump caps" and others that were

more illusion than protection.

The Snell Foundation had promulgated the first bicycle helmet stand ard in the U.S.

in 1970, but at the time only a light motorcycle helmet could pass it, and thatmeant two pounds of unvented helmet.

Very few, if any, helmets were certified to it, and none made their way to bike shops. Since

there was no commonly used standard, there was no way for the consumer to find out which

helmets were most protective.

In 1974 the Washington Area Bicyclist Association despaired of finding

information on the relative protection of helmet brands and formed a Helmet

Committee to collect data from ride testing. WABA procured helmets from many

sources and began a series of ride tests. At that time we found that the helmets on

the market mostly had some kind of shell with a squishy foam liner. None had

crushable EPS (picnic cooler) foam until the Bell Biker (below) and the Mountain

Safety Research bike helmet came to market in the mid -1970's.


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Bike club experience quickly showed that both were far better in performance than the others

on the market

The MSR bike helmet was an adaptation of their mountain climbing helmet. It had

EPS foam in a ring around the headband, with the top protected to a lesser extent

with a suspension system whose nylon straps attached to the shell with deformable

hooks. Curves in the hooks were designed to straighten out on impact as an energy

management technique. In a few months MSR apparently realized that the

suspension system was less effective than the foam section, and that riders impact

all over the helmet. They provided EPS glue -on pads to go in the upper area, with a

wedge-shaped EPS section between each of the nylon straps of the suspension

system. The shell of the MSR was a stiff polycarbonate, probably GE's Lexan.

The Bell Biker also had a hard Lexan shell, and it had a full EPS liner. When it

was introduced other manufacturers eventually followed Bell's lead and this type of

helmet dominated for a decade. There were still some helmets produced with hard

shells and squishy foam liners by Pro -Tec and others, and a notable design called

the Skid Lid with strips of hard shell backed by squishy foam.

In the early 1980's Dr. George Snively of the Snell Foundation agreed to work with

WABA's helmet committee to provide us with helmet testing. We procured thehelmets, did a ride test, and shipped them to Snell, where Dr. Snively tested them

for strap strength and impact protection in Snell's lab. Snell maintained a strict

division between their certification testing and the testing they did for us. By that

time there were 20 or so helmets to be tested, and the testing showed that the Bell

Biker, and updated MSR and a helmet known as the Bailen Bike Bucket (below)

were the best of the lot.


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The Bailen was the first "one size fits all" bike helmet, with an adjustable ring inside that fitsizes 6 7/8 to 8. It had no vents, and both internal and external hard shells.

Dr. Snively gave generously of his time and unparalled expertise to educate the

WABA testers in helmetry and helmet standards. WABA's Tom Balderston wrote

up the findings and Bicycling Magazine published them--in the face of lawsuit

threats from manufacturers--in 1983. That article was a landmark, and alerted

consumers to the vast differences in performance between helmets on the market.

It helped pave the way for standards to develop.

In 1984 the ANSI headgear committee adopted ANSI Z80.4, the first workable

bike helmet standard for the US. The Snell Foundation revised their own standardthe next year to adjust the requirements to more realistic levels for bicycle riding

impacts. In just a year or so the junk that could not meet the ANSI standard was

swept from the market, in some cases by lawsuits. Mid -1980's bike helmets were

characterized by EPS foam liners, with ABS or polycarbonate hard shells.

Virtually all of them had a simple strap design shaped like a Y on each side. For

buckles, most had d-rings or plastic buckles made by Fastex.

In the early 1980's the next big step in bicycle helmet design occurred when Bell

introduced their "L'il Bell Shell" infant-toddler design.


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To make the helmet lighter, Bell dropped the outer shell, producing a thick all-EPS helmetthat was highly protective. The design was actually an adaptation of a helmet Bell had

produced for pediatricians to protect child heads after surgery. Bell limited the idea to toddlerhelmets in the belief that adult helmets would always require a hard shell. In 1986 a designer

named Jim Gentes designed an adult bike helmet with some vents and no shell, and formedGiro Sport Design to market the concept. The lighter weight was an instant hit, and Giro

began selling large quantities of the helmets to racers and others who could afford the high

price.


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Giro used an outer cover of thin lycra cloth. The cover was hand sewn in the US and was one

of the major costs of producing the helmet.

The all-EPS helmets that followed soon distinguished themselves as protective helmets that

had an unfortunate tendency to catastrophic failure in the first blow. To hold the all-EPS

designs together better, Pro Tec introduced two or three years later an all-EPS helmet with

internal reinforcing. Their Mirage model had a nylon mesh inserted in the foam, clearly

visible in the vents.


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The mesh is visible in the vents in the second photo above. It worked well, and has been

followed by thousands of other designs using internal reinforcing to hold the foam together.The early ones, including the Pro Tec, still had cloth covers and no outer shell.

The next big design step appeared about 1990 with the reintroduction of a shell to

cover the EPS, this time in PET (milk jug plastic) and other thin, tough plastics.

The shell helped to hold the foam together in an impact and lowered the sliding

resistance of the helmet to make it skid more easily on pavement, both important

safety features. In just a few years this thin shell design took over the market,

replacing both the remaining hard shells and the cloth -covered EPS-only designs.

The shell was produced separatel y from the interior foam, and then glued or taped

on.


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Another innovation in the early 1990's was molding the foam in the thin shell, by placing the

shell in the mold first, then expanding the EPS bead to fill it. The heat of the process then

requires a higher grade of shell than PET, usually a polycarbonate, since PET will melt at the

temperatures in the mold. The technique fills the shell completely, with no gaps between the

foam and shell unless there are quality control problems.

That permitted the designer to produce a more protective helmet with the same thickness.


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Designers quickly found that the same technique permitted them to thin the helmet down for

more appealing styling and to open up more vents.

In the years since 1990 some manufacturers have continued making the hard shell,

mostly in ABS plastic. Most of their models are for skate-style helmets only, where

the style endures. In 2001 a company called Hopus Technologies / Aegis

Helmets managed to develop a technique to make molded-in-the-shell helmets

using an ABS hard shell.

At about the same time as thin shells, manufacturers added a supplementalstabilizer in the rear of many models in the form of a plastic patch or cloth strap in

the rear to hook below the bulge in most riders' heads (the occipital bone) and hold

the helmet on better. Many innovations in these stabilizer designs have followed.

The most efficient shape for a helmet in a crash resembles a bowling ball. Round,

smooth surfaces slide well and "scrub off" energy from a crash, while avoiding any

tendency for the helmet to snag and jerk the rider's neck. This has been

demonstrated in lab tests. But designers began flogging "aerodynamic" designs in

the late 1980's as the aero craze peaked. Greg LeMond wore one in a famous time

trial where he came from behind to win the Tour de France. Bicycle helmet shapes

have become elongated ever since, basically as a fashion trend, since the aeroquality of the helmet has no real effect at the speeds most riders travel.


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An unfortunate trend in shapes became evident in the late 1990's as designers began

producing helmets with ridges, rear projections and squared-off lines to give them a more

stylish appearance. We have ranted against the trend, but without much effect, and have beenunable to get provisions in any standard requiring low sliding resistance. We could only hopethe fashion will reverse as fashions always do, and lead us back to smoother designs. Finally

in 2004 there were signs of at least a few rounder, smoother designs produced for the"commuter helmet" niche in the market. Bell introduced the Metro, followed quickly by a

number of others.

The Metro was an intentionally clunky design, but SixSixOne found a design in China shortly

thereafter and brought the helmet on the right below, the Allride, to the US market. Weak

marketing doomed it to low sales, and the company dropped it from their line after 2005. But

the original producer brought it back for 2006 as the Vcan VCK37 (on left below).


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In 2006 the round helmet trend advanced in Europe with the introduction of the CASCO

Warp II helmet, a very round and smooth design for track racers. The manufacturer advertisesit as a more aerodynamic design based on automotive research. Track racers in the UK were

early adopters and their demand alone led to backorders for the helmet. It is not clear why theaerodynamic claim led buyers to reject all of the aero research of manufacturers of the

elongated designs.

The extreme of the elongated aerodynamic style is the chrono helmet developed in

the 1980's for Olympic time trials. This one has a rounded front and usually has a

very long tail that rests on the riders back when in the tuck position used by time

trialers. Vents are minimal or non-existant. Early models had only a shell without

impact protection, but in 2002 Louis Garneau introduced one that met the

requirements of the US CPSC standard, and various manufacturers soon began

making them to the European CEN standard. We have a page up on current chrono

helmets.

Another major helmet shape that crept into bicycle helmets is the "skate-shaped"

helmet. Originally developed for skateboarders by Pro -Tec, the style has lower rear

coverage, small round vents in the front and even smaller round vents in a circle on

top.


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The skate style helmet is almost always a hard shell with ABS plastic. Although originallyusing a squishy rebounding foam that provided the multi-impact performance needed for

aggessive skateboarding, the helmets evolved into bicycle helmets because the squishy foam

would not perform in harder impacts called out by bicycle helmet standards. After 1999 when

the CPSC standard came into effect, big-box retailers were not willing to put a helmet on the

floor that could be bought as a bike helmet but did not meet the CPSC standard. As a result,most skateboarders now are buying single-crash bike helmets with crushable EPS foam

inside.A few manufacturersare making helmets with EPP foam or other foam that can becertified to both the ASTM skateboard helmet standard and the bicycle helmet standard.

Foams

In the late 80's or early 90's came the introduction of new foam types to replace the simple

EPS picnic cooler foam that dates from the 1950's. One of the first was EPP, Expanded

Polypropylene, a foam that looks much like EPS but has a slightly rubbery feel. It is

extensively used in the automobile industry. EPP has the desirable characteristic of slow

return to its original shape after an impact, and is therefore well suited to multi-impact

helmets. It is generally considered to have slightly more rebound on initial impact than EPS,

and a little less impact attenuation for a given thickness. Although Aria Sonics had an EPP

helmet for five years or more, the design was never appreciated by consumers, and its

marketing was inadequate to establish its advantages. A Canadian company called Headstart

introduced EPP designs in the mid-1990's, but the helmets were not well finished and did not

have the quality appearance that was required to sell in the U.S. market by that time.

In the early 1990's an advance in EPS from General Electric called GECET was

introduced to bicycle helmets. Although GE had not originally designed its

combination foam and resin product for bicycle helmets, it was appreciated for its

resistance to catastrophic failure, permitting manufacturers to open up larger vents

and thin out liners in some places.


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Another foam introduced in the 1990's was Expanded Polyurethane, or EPU. This

is a slightly heavier foam with exceptionally small and uniform cells. It skins over

in the mold, producing a shell-like cover on the lower section below the regular

plastic shell.

EPU can be molded in the shell or the shell can be applied afterwards. It has almost no

rebound and performs well in lab tests. Taiwanese manufacturers are the main users of EPU,and helmets made of it are among those on the Snell B-95 certification list, indicating that

they perform well indeed. There may be some environmental issues related to the production

process for EPU, however.

In 2001 a ski helmet company known as Team Wendy or W Helmets show ed a

new helmet with a foam they call Zorbium.


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It is a squishy foam that the company claims has extraordinary energy management

capabilities, with a "rate-sensitive" quality that makes it squishy enough to give in a lesserimpact but causes it to stiffen to handle a harder hit. Although the concept is apparently

sound, we never could get any test data on production models. The foam is heavy and absorbs

sweat readily. W Helmets remains the only user of this foam, and their implementation hasbeen directed toward ski models. By 2010 they were no longer making civilian helmets.

It may seem surprising that most bicycle helmets are still made of the EPS

developed in the 1950's. Over the years we have heard of various experimental

foams that were about to break open the market with astounding performance

characteristics, but few have materialized in actual production, and their benefits

are not readily apparent. There are probably limits to such properties as foam

thickness. Basic laws of physics make it evident that it would be very difficult to

stop a rider's head from 14 MPH to 0 MPH in less than, say, a half inch of crush

space, without exceeding the 200, 250 or 300 g limits in bicycle helmet standards.

So better foam may not produce much improvement unless the crush rate of the

EPS has some undesirable characteristics or multi impact is important for the sport.

Thicker helmets could do more, but consumers reject them. Some attempts have

been made to improve the way EPS works, mostly with dual -density formulations.

The cone-head technology developed by Don Morgan and marketed in 2010 is

designed to make the transition between layers smoother.

In the years since 2000 several newer foams have appeared, associated with

marketing labels like "Brock foam," or "cross-linked foam." The latter has been

rumored since well before 2000. Pro Tec has SPX foam, a different formulation of

EPP, and other companies are using TAU or Re-up foam, again differentformulations of EPS or EPP. We have a page up on foams if you want more detail.

Buckles and Straps

The basic bicycle helmet strap was made of nylon beginning with the early MSR and Belldesigns. In the late 1990's other materials including polypropylene replaced some of the

nylon, but the resultant strap is difficult to distinguish from nylon. Each formulation has its

own characteristics, affecting such parameters as buckle slippage.

The first fasteners were mostly D-rings, a design borrowed from motorcyclehelmets where the strap is fed through two d-shaped rings and doubled back

through them to grip.


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This is done each time the helmet is put on. Making the rings from stainless steel ensures

resistance to corrosion from sweat. This design is simple, very strong, reliable for a decade ormore of use and ensures that the rider can achieve optimum tightness on every wearing. But

many bicycle riders find it fussy and sometimes difficult to fasten, and triathletes complainthat it takes two hands. Instead, manufacturers turned to plastic buckles of many designs,

dominated by the design produced by Fastex using a male two-prong buckle sliding into a

female mate with side-squeeze release achieved by pressing the two male prongs together.

Strap junctions and other fitting pieces for helmet straps have advanced from flimsy plastic

parts or simple sewn connections to much more elaborate fittings to facilitate adjustment.

Some have cam locks or other means of locking the strap when adjustment has been

achieved. Most have a "strap creep" problem, resulting in loosening of straps with repeated

use. This can sometimes be limited by adding rubber rings to grip the strap where it enters the

fitting. Although fitting a helmet well is critical for good performance, no manufacturer has

yet produced a helmet that is self-adjusting when first worn. That is perhaps the greatest


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bicycle helmet advance waiting to be made. After all these years of bicycle helmet use, fit is

still our biggest problem.

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helmet design