First look: Giro Synthe semi-aero road helmet

Giro claims the Synthe is cooler and more aerodynamic than the Aeon and Air Attack helmets already in the company's line

PRESCOTT, Ariz. (VN) — Giro’s new Synthe is built in the spirit of compromise — a jack of all, master of none, it would seem.

Or, if you ask Giro, it’s a master of all.

The Synthe is strung between apparently incompatible ideals: low weight, aerodynamics, cooling, safety, and good looks. Oddly enough, that’s exactly where its creators wanted it.

Giro already has an aero road helmet, the Air Attack, with minimal venting for minimal drag. It already has a traditional, light, heavily ventilated helmet, the Aeon. The Synthe sits right in the middle, but Giro claims it actually surpasses the two specialists in a few key areas.

The 250-gram Synthe is 16 percent faster and 2 percent cooler than the Aeon, and 13 percent lighter than the Air Attack, Giro claims. Most impressively, Giro claims it’s even faster than the Air Attack at the head angles most frequently used by road riders.

The Synthe exists in the same space as Specialized’s Evade and the Smith Overtake — light enough, cool enough, with an eye towards aerodynamics, as everything seems to have these days. It is supposed to be a quiver killer, a single helmet that can do it all. But did Giro hit the mark?

Giro Synthe aero claims

Giro claims that the Synthe decreases drag by 16 percent relative to the Aeon, and is only actually a bit faster than the Air Attack in a normal, somewhat upright riding position. The Air Attack is only faster when a rider’s head is tucked down.

Giro also claims that the Synthe is nine grams of drag faster than the Specialized Evade, which certainly is its primary competitor.

The major difference between the Synthe and the Aeon is the quantity and shape of the vents. Fewer, larger vents on the Synthe allow Giro to leave large, solid panels on the top of the helmet, decreasing drag. While the Aeon features 24 small and evenly spaced vents throughout the helmet, the Synthe has fewer, larger vents, concentrated on the forehead and back to facilitate airflow at high speeds while minimizing drag.

It has a few subtle aero tricks up its sleeve, too. The solid mesh panels on the side of the Synthe control the air flow’s boundary layer. Air flow on the front of the helmet gets caught up, increasing pressure, then pushes out of those solid mesh panels, creating a boundary layer as it evacuates the helmet. Giro has found that big vents on the side of the helmet have a large negative impact on drag — that’s why there aren’t any on the Air Attack, and why Giro had to find a way to control the flow in that area on the Synthe.

Making such aero claims requires a bit of backstory. All of Giro’s claims are based off of a figure called wind average drag, a method of averaging drag figures across all angles based on the amount of time the helmet is likely to see wind from those aspects.

All testing is done at 25 miles per hour, something of a standard in the cycling industry, and at a 30-degree head angle. The 30-degree head angle replicates a head-up position when riding in the hoods or drops — in other words, the position most of us will ride in most often.

Giro also tests at a 60-degree head angle, replicating a rider with his or her head down. At this angle, the Air Attack remains significantly faster — on the order of 16 grams of drag at 25 miles per hour. So if you’re a sprinter, or a head-down time trialist, the Air Attack is still faster.

Cooling claims

The Synthe has only 19 vents to the Aeon’s 24. But the science of cooling has moved far beyond counting the number of vents in a helmet. The new model has a wide collection of cooling features, including the excellent RocLoc Air fit system, a number of wide cooling channels inside the helmet itself, and those big front and rear vents to evacuate air.

Cooling is a subjective measure, highly dependent on head angle, ride speed, how much hair you have, etc. But Giro claims that the Synthe, at a normal head angle (30 degrees), is actually 2 percent cooler than the Aeon at normal riding speeds.

That’s a big deal, and if true, Giro may be shooting itself in the foot. Why buy the Aeon if the Synthe is just as cool and far more aerodynamic? The 30-gram weight difference is surely not enough of a selling point.

Giro tests cooling using a device it calls the Therminator, essentially an aluminum head covered in 24 temperature sensors, which allow the company to create a map of heat across the skull. The Therminator is put in a wind tunnel with a helmet on. Wind is blown at it at 25 miles per hour, and Giro tracks the rate of cooling.

The test is certainly relevant for high-speed, flat riding, but Giro hasn’t done extensive testing at lower speeds. It admits that it needs to, and has already started collecting data. This leaves a big question unanswered: is the Synthe cooler than the Aeon when you’re climbing, moving far slower than 25 miles per hour? The Synthe’s design is based around moving air front to back — it may not be as effective as the Aeon at moving hot air up and out, given the solid panels across its top.

Synthe fit and finish

The helmets available at Giro’s launch in Scottsdale, Arizona are not production models, and a few of the padding and strap details are yet to be finalized. But the basics will remain the same — the Synthe will utilize the same RocLoc Air fit system that debuted on the Air Attack, which improves airflow by pulling the helmet up and away from the skull. It’s a highly effective, and comfortable system.

Fit is essentially unchanged from the Aeon; put the Synthe on and the only noticeable difference is the lighter feel of the RocLoc Air fit system. Sizing is identical, so if you already ride a Giro, there’s no need to guess.

The eyewear docks, built into the mesh, boundary-layer-inducing side panels, are a fantastic feature. Of course no helmet is compatible with all glasses, but Giro tested with many different types, and the docking system works very well with the Oakley RadarLocks.

The Synthe is unquestionably the most attractive aero road helmet on the market, mostly because it doesn’t look like an aero road helmet at all. It doesn’t look dorky; it doesn’t look like one of Batman’s accessories. It looks like a mellowed-out Aeon, or a sleeker Aspect — the helmet Giro debuted as part of its New Road line. It cuts an exceptional low profile, so mushroom-head is no longer a concern. Regardless of the aero and cooling claims, it’s a good looking lid.

The Synthe will retail for $250, and availability is set for December 2014. Check back for a full ride report following three hours of hot Arizona desert riding.

Giro provided travel and lodging for media attending the Synthe press event.