The Torqued Wrench: A tale of helmet tails

CREVAUX, France (VN) —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.