i*********5
发帖数: 19210 | 1 【 以下文字转载自 Tri 讨论区 】
发信人: ironman2015 (IMMT 2013), 信区: Tri
标 题: The Tale Of The Disappearing Aero Helmet Tail
发信站: BBS 未名空间站 (Wed Sep 11 16:32:03 2013, 美东)
http://triathlete-europe.competitor.com/2013/07/22/the-tale-of-
Greg LeMond's Giro time trial helmet was ahead of its time, more similar to
the ultra-modern designs we see today than any of the long-tail designs of
the last two decades.
Specialized sponsors Saxo-Tinkoff, Omega Pharm-Quick Step, and Astana in
this year's Tour. All were wearing the company's McLaren time trial helmet,
except world champion Tony Martin, who rides the older TT2. According to
Specialized, the McLaren is designed to increase aerodynamic "robustness"&#
157; or the variety of positions and wind angles in which it retains its low
drag figures. So it works better, more of the time.
Cadel Evans wore this special red Giro in the stage 4 team time trial while
the rest of his team wore black, "so we can spot him," Jim Ochowicz told
VeloNews and the Sydney Morning Herald just before the stage. It's
advantageous for both mechanics and other riders to instantly know if their
captain is having trouble. The helmet uses a very short tail so he can tuck
his head into his shoulders. | i*********5
发帖数: 19210 | 2 The dawn of the aero helmet is easy to pinpoint: Greg LeMond, 1989, with the
Giro Aerohead. He may not have been the first to fair his noggin, but he
did so on the greatest of stages, and with the greatest of results.
Since that ride into Paris, during which LeMond made up the 50-second
deficit required to knock Laurent Fignon off the top step of the podium at
the Tour de France, the aero helmet has grown up. It’s matured, changing
with each passing birthday, as aerodynamic engineers sought the greatest
possible advantage.
LeMond’s Giro was teardrop-shaped, complete with a mid-length tail until
the UCI required him to lop the back end off for the final time trial,
resulting in a snub-tailed shape.
Within a few years, his fully-functional foam helmet soon gave way to what
were little more than hair fairings — thin, plastic shells that would do no
more for a falling rider than a cycling cap.
Slowly, TT helmets grew longer and longer, unencumbered by weight issues
thanks to the thin shells. They stretched backwards based on the best aero
data engineers had at the time: wind tunnel testing. Soon Lance Armstrong
was riding in a helmet that reached half way down his curved back, hooked to
fit the shape. Jan Ullrich’s Uvex stuck a foot up in the air when he put
his head down.
But those were just growing pains. Oddly enough, the time trial helmets of
today want to be just like Dad; they’re closer in design to LeMond’s old
Giro than anything else in the last 20 years. Their tails are short and
stubby, just a few inches long. Some, like Chris Froome’s Kask, have hardly
any tail at all.
Why?
“The bottom line is, you need to design the helmet that has the highest
chance of being the fastest solution for a lot of riders with a lot of
different positions,” explained Specialized aerodynamicist Chris Yu. For
the majority of riders in the majority of riding positions, the long tail is
not that solution.
The key, companies have discovered in the last few years, is what
aerodynamicists like Yu and Rob Wesson, one of Giro’s aerodynamics
engineers, call “robustness.” The term refers to the ability of a helmet
to maintain its aerodynamic advantage across a wide array of wind and rider
positions, and it’s a design goal that only truly came to light once
research began to extend beyond the wind tunnel.
“As recent as even five years ago we (and our competition) were making
regular trips to wind tunnels and going about aero research in the same way,
” Giro’s Wesson said via email. “Your two choices were to test with a
real athlete (rare and more difficult) or set up your optimized TT position
mannequin. Either one gave you fairly accurate and consistent results in
that one optimized position.”
But relying solely on such testing didn’t provide any clues into how robust
a helmet design would be. The parameters were too tight, the conditions too
repeatable. “Mannequins never get tired, and athletes never do a real TT
effort while in the tunnels, so your aero results were always based on short
, optimized window of data. Real world riding and racing is not like this,”
Wesson explained. “Depending on the TT, many athletes spend a higher
percentage of their time looking straight down than they do looking forward.”
According to Wesson, between that head movement and any changes in wind,
course profile, and body movement (between fresh legs and tired legs, for
instance), “and suddenly you’ve completely wiped out what you thought was
an aero advantage from the tunnel.”
Today, the industry’s aerodynamics experts have brought testing into the
real world. They use power meters on open roads and velodromes, and combine
those data with wind tunnel work and computer modeling, called computational
fluid dynamics (CFD, for short), to design helmets that will work for more
people, more often.
The results were visible in the time trials of this year’s Tour: shorter,
stubbier helmets that fill a bit of space behind the neck, but don’t extend
any further than a few inches.
“The original thinking was that the tail may actually be increasing drag if
it’s not in the right position or alignment,” like if a rider stuck his
head down and pointed the tail up in the air, Yu said.
“There was a push to get rid of the tail to make the helmet a little more
robust to moving the head around. However, we, and others, have found that
having some sort of tail is still critical to making a helmet fast,” Yu
said. “Without a tail, or one that’s too short, you end up back at square
one with effectively a sphere. [That] is aerodynamically not a very
efficient shape.”
Yu and his Specialized team, along with other helmet makers across the
industry, spent considerable time playing with tail length, endeavoring to
find out just how short they could go before the drag shot up.
“It’s a compromise game,” he said. “We want to optimize performance as
much as possible for the baseline condition,” or the ideal position that a
rider will attempt to hold throughout an effort, but still “allow the
helmet to perform well in other conditions and positions.”
Most ended up with the same conclusions: go back to the LeMond model.
Specialized, Giro, Bell, Kask, Ekoi, all of which sponsor Tour teams, have
debuted short TT helmets in the last two years.
Does that mean you should rush out and buy one? Perhaps. But don’t
automatically assume one of the latest snub-tails is the best option for you
. “Body shape, size, riding style and position all need to be considered.
The helmet is no different,” said Wesson.
In general, “riders that don’t or can’t shrug or ‘turtle’ their head as
much benefit more from a longer tail, assuming, and this is the big caveat,
that they can hold their head steady in the optimal position the entire
time,” Yu said. “Riders that bury their head or turtle really well tend to
benefit from shorter-tail helmets.”
But if more than 20 years of wildly variable helmet design teach us anything
, it’s that there is no one-size-fits-all solution. | i*********5
发帖数: 19210 | 3 BMC’s New Giro TT Helmet
These stubby time trial helmets were developed originally for Garmin-Sharp,
with extensive involvement from the team’s sports scientist Robby Ketchell.
But after two years of exclusivity, Giro has made them available to other
teams; it has no plans to offer them for sale yet, but the direction is
clear: The BMC helmet shown here is much more finished than early versions,
which were little more than a shell glued to an existing road helmet. The
big challenge? Passing consumer safety testing. | m******r
发帖数: 9604 | 4 Long live the tail!
l: Greg LeMond's Giro time trial helmet was ahead of its time, more similar
to
【在 i*********5 的大作中提到】
: BMC’s New Giro TT Helmet
: These stubby time trial helmets were developed originally for Garmin-Sharp,
: with extensive involvement from the team’s sports scientist Robby Ketchell.
: But after two years of exclusivity, Giro has made them available to other
: teams; it has no plans to offer them for sale yet, but the direction is
: clear: The BMC helmet shown here is much more finished than early versions,
: which were little more than a shell glued to an existing road helmet. The
: big challenge? Passing consumer safety testing.
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