|
In a proactive stance, Brand S contracted a
series of tests, which I witnessed, to be
conducted at an independent lab in order to
document the edge sharpness of currently used
spokes. The results of the “Technical
Requirements for Determining a Sharp Metal or
Glass Edge in Toys and Other Articles Intended
for Use by Children Under 8 Years of Age (16 CFR
1500.49 in the Code of Federal Regulations) were
that traditional bladed spokes used by various
manufacturers were classified as sharp edges
along with the Brand S spokes. A urethane spoke
edge cover was subsequently developed for all
current Brand S wheels, and when applied, the
spokes were in compliance with federal sharp
edge regulations. The complete results were
communicated to the UCI in written report form.
No modifications, to my knowledge, were done to
bladed spokes used in the peloton. It seemed
that the UCI was satisfied with our efforts.
In early 1998, the UCI issued Brand S another
“concern” about carbon fiber wheels in general.
The UCI was afraid that the mechanical
properties of composite wheels led to vibration
related spinal and wrist injuries. In another
proactive response, Brand S measured the radial
(vertical direction if the bike is upright)
stiffness of many wheels. As a first order
approximation, wheel radial stiffness can be
related to a peak force transmitted to the
rider. It turned out that deep-sectioned metal
wheels were actually stiffer than the majority
of composite wheels at the time. The highest
radial stiffness value that we measured belonged
to a 36-hole Campagnolo Omega V clincher rim –
one that interestingly falls within the current
“traditional” design specifications set forth by
the UCI.
During this same time, and in anticipation of
the UCI’s next move, Brand S developed a test
protocol that identified a wheel’s dynamic
response in the vertical direction. We were thus
able to objectively quantify the amount of
energy absorbed by different wheels during an
impact through exact, repeatable methods. Using
a load cell and an accelerometer it was possible
to identify all dynamic system variables in a
lab environment (stiffness, mass, and damping).
Again, the results were clear – various designs
of conventional spoked wire wheels provided the
greatest “spinal injury” risk to the cyclist.
These results were communicated to the UCI in
report form.
Shortly after these results were submitted
(the end of February, 1998), the UCI replied
that our findings were invalid because the wheel
was not rotating during the test. This
additional requirement set forth by the UCI made
our task significantly more challenging.
At this point, I was feeling that the UCI was
being ridiculous. They were simply not seeing
the forest through the trees. If the UCI was
truly concerned about peak forces and
vibrational effects on riders, they should
simply mandate that all racers use 700x28c tires
inflated to no more than 90 psi. This would
adequately address their concerns. Was there
another agenda, or were they simply that
incompetent?
Nevertheless, Brand S developed a test where
the wheel was allowed to rotate without a tire
on a urethane drum. Intermittently, a “bump” was
introduced between the rim and the roller and
the peak force transmitted to the axle was
monitored via an accelerometer. Once again, the
highest peak forces recorded belonged to the
conventional 36 spoke metal-rimmed wheels. These
results were communicated to the UCI in report
form.
For nearly two months I didn’t hear anything
about the UCI from my supervisor. I thought the
worst was behind us. In late April, we heard
that the UCI was now concerned about the
catastrophic failure modes of composite wheels.
Once again, I figured we had this one in the bag
because we had recently discovered that the
Mavic GEL 280 and the GL330, light tubular rims
that were deemed “safe enough” by the UCI and
the public in the late 1980’s and early 1990’s
to be used in competition, catastrophically
failed at a much lower impact energy level than
current Brand S product. In lab tests that I
conducted, these light “standard” wheels
routinely failed in the 600-800 in-lb range when
rigidly supported by the axle and struck in a
radial direction by a blunt-faced pendulum. We
had it made, or so we thought.
We anticipated that the UCI would not be
willing to accept the results of a static test,
so we set out to develop a dynamic test that
would capture all of the events inherent to a
catastrophic wheel failure during impact. In the
end, our test consisted of attaching the front
end of an old bicycle to the trailer hitch of a
Ford Explorer and towing our bicycle wheel
“trailer” over a raised wooden 2x4 obstacle
angled at 45 degrees to the direction of travel.
We attached sandbags to the frame and by design,
our trailer was allowed to pivot vertically
about the front fork dropouts – during impact
the rear end launched the sandbags in a similar
fashion that a rider would be pitched forward
during an impact and thus un-weighting the rear
wheel.
The whole testing process was videotaped and
trailer speeds were monitored using a radar gun
we borrowed from the local police. Some of the
failures were quite dramatic as one could
imagine the consequences of a rim becoming
discontinuous at 30 mph – the sparks flew as the
hub and rear dropouts of the “trailer” scraped
across the ground. We destroyed all types of
wheels (around 50 in total), Brand S ones
included. Again, the deep section wheels were
always stronger, and were able to withstand
higher impact energy levels prior to
catastrophic failure (higher trailer speeds in
this case).
The test was a good test. It satisfied the
primary rule of any kind of destructive failure
test - the failure modes during the test were
consistent with real-life failure modes and the
trends correlated well with theoretical
analysis. The trailer results also correlated
well with our static lab results.
The composite wheels we tested, along with
some deep-sectioned wheels such as the Mavic
CXP-30 survived higher speeds than the low
profile lightweight tubular wheels. Deep section
wheels and the Brand S wheels tested were safer
than these lightweight traditional wheels. We
weren’t alone in our technical opinions.
In fact, David Gordon Wilson (a well respected
engineer and the prestigious author of a book
called Bicycling Science) reviewed our test
documentation and videotape. Wilson produced a
written statement claiming something like: (I am
paraphrasing from memory) “The tests were
convincing. The (Brand S) wheels resisted
catastrophic damage to significantly higher
speeds than did the metal-spoked wheels.”
In early June, 1998 Brand S sent the results
of its catastrophic failure testing to the UCI
in report form – we attached the review and
written statement of David Gordon Wilson.
The UCI was silent for nearly a year. In
April 1999, the UCI sent a package to Brand S
that included the description of proposed
regulatory tests that would govern “acceptable”
bicycle wheels. They solicited comments from us.
I sent off a company response with dozens of
questions and suggestions for improved test
methodology – none of these questions were
answered and none of the suggestions were
implemented.
The proposed tests included the following:
1. Measurement of the “stiffness of a bicycle
wheel passing over obstacles
This test was to be the UCI’s attempt at
eliminating wheel induced spinal/hand injuries.
2. Static test on a bicycle wheel
This test was to measure the lateral stiffness
of wheels. The goal of this test remains
unclear.
3. Impact test on a bicycle wheel
This test was identical in as much as I can
remember to the current “rupture” test – with
the goal being to determine “consequences” of
catastrophically failed bicycle wheels.
In November 1999, I was sent to the UCI
selected lab (CRIF) in Liege, Belgium to survey
the facility and witness Brand S wheels being
subjected to the impact test. While my family
dined on a nice juicy turkey during
Thanksgiving, I had the pleasure of attempting
to navigate the Belgian public transportation
system. My family had a better time that day.
During the latter stages of the tests, in
which Jean Wauthier (UCI representative) was
present along with another Brand S colleague of
mine, it became clear in my mind that the
particular model of Brand S wheels being
evaluated would never be on the conforming list
once it was published. This feeling was cemented
after my colleague overheard the UCI approved
technicians comment to Wauthier “I think we just
got what we were after” (or words to that
effect) during the catastrophic failure of one
of the Brand S wheels.
The Final Test
The current UCI rupture test protocol is
quite simple. A bicycle wheel is rigidly
supported by its axle, just as if it were in an
infinitely stiff bicycle fork/dropout. A 100 kg
sled is propelled at 10 km/hr into the wheel.
The striking face has a radius of curvature to
it (from memory it would not be defined as a
sharp corner). Wheels are struck in two
different configurations both horizontal in
direction (impact force is applied in the same
direction as the longitudinal axis of the
bicycle. The first configuration replicates the
“normal” occurrence of striking a solid brick
wall head on.
The usage of the word “normal” is significant,
because the UCI includes it in the actual
wording of rule 1.3.018. I don’t know where the
UCI races its bikes, but in no way would I
consider running into a brick wall a “normal”
loading situation. In this configuration, the
impact force is applied at the rim through the
center of the axle in the plane of the line of
symmetry of the rim cross-section.
If I did run into a brick wall, the least of
my concerns and the riders behind me who might
suffer the consequences of my actions would be
the state of my wheels. It is a much better idea
to approve race courses that don’t have walls in
the wrong places, or if there are walls on the
periphery of the course that they are properly
buffered with hay bales or other safety
enclosures. Perhaps Chris Boardman might not
have been eliminated during the 98 Tour de
France if the wall he collided with were
properly buffered. Similarly, many young
European racing cyclists might still be among
the living, and they might not have experienced
career-ending injuries, if the governing body
had properly prepared and secured its race
courses.
The second impact configuration attempts to
mimic the more often-encountered pothole impact.
The horizontal impact force is located at a
vertical point midway between the axle and the
road contact point. Anyone who has done a lot of
bike riding in a tight pack has encountered this
situation.
Just imagine it. It is a hard left to right
cross-wind section. The long, angry line is
drawn out on the right-most twelve inches of
road. You are on the rivet focusing on the wheel
of the poor sap in front of you when, WHAM, you
drill a pothole, pinch both tubes and dent both
rims. Your day is done. Good thing you were
riding on strong wheels, eh?
I don’t have too many complaints about this
configuration of the UCI test protocol. The main
contention that I do have with the test in
general is the UCI’s selection of the impact
energy and the interpretation of the test
results. These will be discussed later on.
It is interesting to note that the UCI backed
away from its initial concerns of sharp edges
and spinal/hand injuries in its final wheel
rule. Were they just on a Brand S fishing
expedition? Would too many “standard” wheels be
deemed unsafe? The UCI would not comment when
posed with these questions.
The UCI chose not to determine and control an
acceptable catastrophic failure strength of
bicycle wheels. In the end, the UCI focused
solely on controlling the failure mode during
catastrophic impacts as its “safe enough”
criteria.
Quite simply, the UCI has stated with its
ruling and test method, that if a new wheel
fails in the same catastrophic manner as a
standard, or “traditional” style wheel, it is
safe to use in a mass start event. It does not
matter what the ultimate load carrying capacity
of the wheel is, only that it collapses into
itself and that all pieces remain attached
without being expelled out of the plane of the
wheel.
Holes in the Test Protocol
There are several areas that the UCI has
failed to address in their determination of a
safety standard for bicycle wheels. First, the
failure criteria are subjective in nature –
reviewing high-speed film to determine which
type of catastrophic failure is acceptable is a
poor evaluation technique – any type of
catastrophic failure at normal impact energy
levels is unacceptable. The UCI has not defined
its definition of the “normal” load spectra of
bicycle wheels - this semantic detail, seems to
me, to be rather important.
I assume that it is believed by the UCI that
by upholding these subjective evaluation
criteria, the consequences of a failed wheel
will be eliminated. In its essence, the UCI is
saying that the consequences of one type of
catastrophic failure are somehow superior to the
consequences of another type of catastrophic
failure. This begs the objective question: If
the overall goal were rider safety, wouldn’t one
want to eliminate catastrophic failures in their
entirety for any type of “normally encountered”
impact?
The solution path to this problem of
determining the magnitude of “normal” impacts
with an unlimited budget is quite simple. It
simply requires that a bicycle be instrumented
with strain gauges and a portable data
acquisition system. The UCI had plenty of time
and money to pursue this method.
Once the “normal” load spectra was determined
for wheels one could simply apply a generous
factor of safety to these real time acquired
force values – lets say twice the magnitude of
these forces (a factor of safety of 2). Finally,
a lab test to accurately and repeatably
reproduce these specified impact forces
(preserving realistic strain rate values) would
be necessary. A simple, objective, and
meaningful passing criterion could be proposed,
such as: any wheel that cannot support a 100 kg
mass after being subjected to the lab protocol
is deemed unsafe.
Another hole in the protocol is that the
impact energy level specified by the UCI is
unrealistic. As I mentioned earlier, lab tests
that I have conducted have shown that the
lightweight tubular wheels that were deemed safe
enough by the UCI 15 years ago, catastrophically
fail (are unable to support any radial or
lateral loads – i.e, the rim becomes
discontinuous) in the 600-800 in-lb impact
energy range. I am unaware of an excessive
amount of wheel failures during the time period
that these rims were popular. It seems that the
public, and their lawyers, have determined that
these lightweight tubular wheels were “safe
enough” for public consumption.
The UCI specifies an impact energy level that
is in excess of five times the energy required
to catastrophically fail these popular
lightweight wheels of the past. What is to be
learned from such an aggressively specified
energy level? If you hit something hard enough,
it is going to fail. The key lies in determining
an industry/UCI determined “safe enough” wheel
and then defining precisely the point at which
this structure fails. Anything weaker than this
baseline wheel structure should be deemed
“unsafe” for mass start competition.
All wheels during the rupture test are
impacted with an energy level of 386 joules
(around 3400 in-lbs). For a rigidly fixtured
bicycle component, this energy level is not
“normal”. The Consumer Product Safety Commision
(CPSC) regulates bicycle forks. In its analysis,
the CPSC says that any fork rigidly fixtured
with a three-inch v-block that can withstand 350
in-lb of impact energy without failure is “safe
enough”. The UCI prescribes an impact energy
level that is nearly 10 times the energy deemed
“safe enough” by the CPSC for fork impacts. I
can understand a factor of safety of two or
maybe even three, but ten? Someone is not doing
his or her homework at the UCI. When will we see
fork/frame rupture tests?
The high energy level inherent to the UCI
test produces failure modes that are
inconsistent with actual usage for certain
styles of wheels. It should be clear that if an
actual wheel affixed to a frame and fork were
impacted with these excessive energy levels, the
wheel would survive and the fork/frame would be
destroyed. The Internet is filled with examples
of this phenomenon or check out this link to see
which is stronger
– deep section wheels or a bicycle frame.
Examples of odd failure modes during the UCI
test have been given by anonymous sources within
the UCI itself: “sealed bearings are seized and
axles are almost always bent during the
(rupture) test” (these were two failure modes
that I witnessed with Brand S wheels when
subjected to the UCI rupture test). The
anonymous source continues, “If the rim itself
is very strong, spoke holes in the hub are
ovalized to major dimensions nearly twice their
original specification and multiple spokes, up
to half of the total number, break.”
When is the last time you have seen a wheel
exhibit all of these failure modes during in
impact with a pothole? I have seen a few wheels
that were damaged during races due to large
impacts and none of them had bent axles or
ovalized hub spoke holes. Most of them had flat
spotted/dented rims that were subsequently
replaced using the original hubs and spokes.
Riding a bicycle requires balance and I don’t
believe humans can do it well enough to allow
the impact forces the UCI is using in its test
to be seen during normal use. The rider will
simply crashe as a result of the impact and she
and her bike are subsequently accelerated in
three dimensions. Wheels in real life simply do
not experience forces of the magnitude the UCI
is implementing in its lab test.
I have also seen the remnants of a Mavic GL
330 after it struck a 4x4 piece of wood at 50
kph during the Vuelta de Bisbee (my brother,
Kirk, was riding it at the time and suffered a
broken collarbone and a separated shoulder). The
rim was in three separate pieces and was clearly
unable to carry a radial or lateral load. As the
UCI sees it though, this type of failure mode is
“safe” – I disagree.
The UCI failure criteria also favor weaker
wheels. Two separate manufacturers and an
anonymous UCI insider have reported that wheel
samples that initially failed the rupture test
were redesigned with weaker rims and
subsequently re-submitted for testing. These
weakened samples passed the test.
Bill Vance, a representative of Zipp, has
made the following statement regarding the
re-design of their 303 clincher wheel which
failed the test due to a spoke pulling out of
the rim, “Since one of the requirements (of the
rupture test) is that the wheel remain whole,
the spoke breakage resulted in the non-passage
of the wheel. Essentially, the strength of the
rim under this particular type of load was
greater than the yield strength of the spokes.
Based on this information, we have re-designed
the laminate structure of the rim to act as a
"crumple zone" while retaining the basic overall
strength.”
The Zipp wheels with the weaker rims should
now collapse in a manner that will be deemed
“safe” by the UCI. Never mind the fact that the
overall wheel integrity (in spite of what Mr.
Vance says, I would rather break a spoke than
“crumple” my rim) was compromised in order to
satisfy the whimsical UCI rupture test failure
criteria. Something is fundamentally wrong with
the UCI test if intentionally weakened rims are
somehow magically deemed to enhance the overall
safety of the wheel and the riders using them.
In Closing
The UCI had a great opportunity to make a
meaningful and important contribution to cycling
during the time period of 1997 to 2002 by
implementing a safety standard for bicycle
wheels. In my opinion, the only thing they have
done is demonstrated their technical
incompetence. Instead of methodically generating
an industry supported baseline wheel as the
“safe enough” benchmark and defining an
objective and meaningful set of failure criteria
(such as the ability to support a 100 kg radial
load after the failure test), the UCI
arbitrarily focused on failure modes of bicycle
wheels subjected to an unrealistic impact energy
level.
Perhaps the UCI will evolve the wheel rule and
test to incorporate the aforementioned
principles – I won’t be holding my breath on
this one though. They ignored these
recommendations in 1999; I reckon they will
ignore them again in 2002.
As I write this in late February, 2002, the
general racing public has not directly been
affected by the UCI wheel rule. The rule only
affects those racing in UCI sanctioned events –
this is a very small segment of the cycling
public. Racers in the U.S. can still ride on the
same wheels they currently use during a USCF
sanctioned race, and I hope that USA Cycling
will stand up to the UCI with regards to this
new rule.
However, behind the scenes, implications of the
ruling by the UCI have already been felt. Some
manufacturers have had to re-design products
scheduled to be released which undoubtedly
incurred higher product development costs. These
higher costs may eventually be passed on to the
consumer. Furthermore, the UCI rupture test
criteria will more than likely become a new
constraint for wheel designers – who wants to be
the first company to assume the legal liability
of selling a product to consumers that a major
international governing body has deemed “unsafe”
to use in mass start racing?
Now then, can someone please remind me why it is
that I am holding this short stick in close
proximity to this large furry creature?
|
