Summary: The Chrono style is a special aerodynamic helmet for time trailing. It is not optimal for street use.

Early chrono models were shells only, and not certified for impact protection. Beginning in 2002, Louis Garneau introduced a chrono model certified to the US CPSC bicycle helmet standard. Two years later the European racing authorities required that chrono helmets used in time trials must meet the European EN 1078 bicycle helmet standard. That began a flurry of retrofitting as manufacturers tried to cram impact foam into their chrono shells. Depending on the amount of room available they were successful, but some had to redesign from scratch. Although they must sell very few of their chrono models, manufacturers believe that they lend prestige to the entire line.

The European CEN standard is less severe than the US CPSC bicycle helmet standard. Helmets built only to the CEN standard are less protective. One example of the difference is that CEN helmets are tested in 1.5 meter drops on the flat anvil, while a CPSC helmet has to perform at 2.0 meters. CEN helmets can be lighter and thinner.

USA Cycling formerly accepted CEN helmets for races that it sanctions in the US, but has reverted to a CPSC requirement starting January 1, 2010, as noted in the current USA Cycling Rule Book. In anticipation of that ruling and to sell in the US market, many manufacturers have improved the protection of their chrono helmets.

The tail of a chrono helmet is not an asset for anything but aero shape. It is long and provides a great place to snag your head in a fall, twisting your head and neck. We don't recommend chrono helmets for street or trail use. Here is an email that demonstrates why:

"I was recently in a crash trying to avoid another rider during a triathlon. It was a typical fall with the bike sliding out in front of me and I landed sliding on my elbow, butt and head. This is generally not the most serious kind of crash but my comments are related to the helmet I was wearing, one of the time trial 'aero' helmets which are being used a lot more by triathletes. On my helmet the shell extends 5-6 inches past the head. The rear aero extensions were held intact by the plastic shell covering the helmet but the downward force from the back of my head broke the inner styrofoam shell into several pieces; the back retention clamp broke off; and the rear strap connection which did not go completely through the helmet (i.e. connected only to the styrofoam part of the helmet) also pulled out. With only the front ends of the chin straps attached to it the helmet came off my head."

Note that using a helmet like that in traffic, where the first hit is likely to be on a car, having the helmet come off could mean hitting the pavement with a bare head. In a time trial there is normally only one really hard impact, on the road.

Riding in a chrono helmet is not simple if you want the full aero effect. Racers train in wind tunnels for best positioning because a degree or two of helmet tilt causes very large changes in wind resistance. If you have a long tail helmet, the tail must lie flat against your back for aerodynamics, so you can't tilt your head to look down at your computer or check your gears or relax your neck muscles without poking the tail up into the windstream. Some riders use a humped over crouch, while others get down and flatten the back. If you have to stand on a hill you will lose the advantage unless you have practiced riding out of the saddle but bent over in a tuck. Those variables require a matching helmet shape for maximum efficiency.

Long tail chrono helmets may be on their way out in any event. Casco claims their extremely round helmet performs better in actual riding, and this article about helmets used in the 2009 Tour indicates that Giro is shortening their next model.

Can a dimpled surface that burbles air like a dimpled golf ball improve aerodynamics? Casco has used a section of six raised rubber dimples in the rear to lower air adhesion there. The Carrera Intruder has two panels of stippled material glued into indentations along the surface for a dimpled effect up the front, along the top and down part of the tail. The Lazer Tardiz has a dimpled rear section. Louis Garneau's Superleggera has a dimpled front section. So there is some indication that dimples can help, but no agreement on where they should be.

Vents are another question mark. Some helmets have none, or only in the rear. Some have small ones. And at the other end of the spectrum some have generous ones. The rider will generate heat in a maximum effort time trial. Is it worth giving up some aerodynamic advantage to cool the head? The answer may be different for different riders, since some give off more heat from the head than others. Lazer is the only one to claim that air taken in through the front vents exits at the rear and pushes the helmet forward. We would have to be convinced of that, since conventional wisdom has always been that maximum aerodynamics means no vents at all.

Weights shown below are the manfacturers' claim. Accuracy is likely to vary, and there are size and accessory differences, so weighing the helmet yourself is always the only way to be sure.

Chrono Helmet Models

Casco Warp II This 2006 German helmet is an almost perfectly round and smooth track sprinter's helmet with an above-the-nose shield completing the rounding.


The shape is almost flawless for crashing. Casco claims it is equally flawless for aerodynamics "according to the latest findings of the automobile industry." This seems like a reaction to the aero tails that have set the fashion in chrono and other high end bicycle helmets for the last decade. Casco has used a section of six raised rubber dimples in the rear to lower air adhesion there. It has 12 tiny round vents that look like hollow rivets. It costs 250 Euros and only meets the CEN standard.