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Bicycle Helmet Safety Institute



Chrono Bike Helmets for Time Trials




Summary: The Chrono style is a special aerodynamic helmet for time trialing. It is not suitable for street use. The tail can be a hazard in a crash.


Chrono helmets are a very special type that is optimized for aerodynamics for use in time trials. The aero shape is advantageous at time trial speeds, primarily above 20 mph, so it is not of much use for ordinary street riding.

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, and usually are.

USA Cycling formerly accepted CEN helmets for races that it sanctions in the US, but 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 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. So the tail is a hazard. Here is the Snell Foundation's warning label, required on any helmet meeting their B-90TT or B-95TT standards for time trial helmets:

"WARNING: THIS HELMET IS NOT INTENDED FOR RECREATIONAL USE. This special use helmet has been designed to provide an aerodynamic benefit through an aerodynamic tail which in a fall or crash may reduce its ability to provide adequate protection. In a fall or crash the aerodynamic tail may cause the helmet to be pushed out of position thereby exposing the head to serious and/or fatal injury. Similarly, in a fall or crash a rider may be exposed to a strangulation and/or choking hazard from the retention system. USE ONLY ON A CLOSED DESIGNATED COURSE IN CONNECTION WITH SANCTIONED TIME TRIALING ACTIVITIES OR COMPETITIVE EVENTS."

That should be a caution to anybody considering the use of a long tail time trial helmet.

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.

The debate on long tail vs. short tail aero helmets continues. Casco opened it in 2009 with claims that their extremely round helmet performed better in actual riding, and there are many shorter helmets on the market now. If your head position is normally low, you may not need a long tail. Pros don't need them if a following car can give them a heads up before turns and they can keep the head down for most of a time trail. But racers with a higher head position and a need to see ahead may want to stick with a long tail model. Only a wind tunnel session can tell you for sure.

In 2013 a new category of aero helmet appeared: the aero road helmet. Not as slick as a chrono time trial helmet, but made more aerodynamic than a normal road helmet, often by covering the vents. Some have adjustable vents, or use vent covers. They are used by pros in some pack races, but abandoned for stages where ventilation becomes critical. They will not improve the average road rider's performance very much, but you might want one for the image, and some have the rounder, smoother profile that we recommend. We don't know if their performance for time trialing is comparable to other designs.

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 and Vorttice have a dimpled front section. So there is some indication that dimples can help, but no agreement on where they should be. And Garneau has a line of raised bumps behind their dimpled section across the crown that they say will accelerate the air and cause it to flow smoothly down the sides in the rear.

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 the only way to be sure.

Chrono Helmet Models

Note: Some of these helmets are reserved for team use and are not available through retail channels. Some may even have been discontinued, since they do not appear in the company's annual catalog and it is difficult to track when a design is no longer produced.

  • BBB Tribase: a European CEN model with a medium long tail in back and four narrow adjustable vents. Fits sizes 55 to 61 cm. Can be found for less than 100 euros.

  • Bell Meteor II: designed by adding foam under the Bell Meteor to meet the CEN standard, so it is limited in size to 59 cm heads and does not meet the US CPSC standard and will not be available in the US market. Weighs 315 grams.

  • Briko Chrono: has two large rear vents and a modest tail that is more rounded than sharply tapered. It has a plastic face shield. It is certified only to the European EN 1078 bike helmet standard, so can't be used in races sanctioned by USA Cycling. Weighs 409 grams/13.1 oz. We don't see the Chrono in Briko's current catalog.

  • Carrera Intruder: classic teardrop shape but with two panels of stippled material glued into indentations on the surface for a dimpled effect. Two top vents and a tiny vent on each side.
  • Carrera TT Viper: a long-tail time trial helmet, with soft countours in the shell, no vents and a section designed to lie flat on the shoulder. Replaced the Intruder in 2013.

  • Casco Warp-Sprint This 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 248 Euros (300 with visor) and according to the CASCO site it is certified to the CPSC standard.

  • Catlike Chrono Aero Plus: a long-tailed time trial helmet that meets the European standard. It is molded in the shell, and has two small vents in front and rear. It fits 55 to 60 cm heads. It retails for 240 euros.

  • Catlike Aero Chrono WT: a long-tailed time trial helmet that is certified by Catlike to meet the CPSC and European standards. It is molded in the shell, and has one large vent in front and rear. The vents are in the shape of the Catlike logo, probably not chosen for its aerodynamic qualities. Ring fit, for 54 to 60 cm heads. It retails in the US for $300 with visor.

  • Cratoni Chrono: Short shell does not fully meet the shoulder or back. No vents. Certified only to the European EN 1078 bike helmet standard, so can't be used in races sanctioned by USA Cycling. Weight is cited as 270 grams, if accurate very light for a chrono. Fits heads 54 to 60cm/21.3 to 23.6 inches.

  • Ekoi Chrono CXR11: a classic long tail time trial helmet, molded in the shell with a two small vents in front and a few in the rear. Fits 56 to 60cm heads. Retail is 129 euros.

  • Ekoi Chrono CXR12: a long tail time trial helmet, molded in the shell with many thin vents in front, sides and rear. Might be a good one for a very very hot day, but the vents are likely to reduce aerodynamic performance. Fits 55 to 60cm heads. Retail is 149 euros.

  • Etto Chrono: a long-tailed time trial helmet, molded in the shell with a two piece shell. Small front vents. Fits sizes 53 to 60 cm.

  • Giro Air Attack Shield: Giro has taken a page from Casco's book and produced an aero helmet that is almost as round and smooth as the Casco Warp. It even has an eye shield to extend the roundness down on the face. The Giro has more vents than the Casco, and lacks the golf ball dimpled surface. It is a thin-shell rather than a hard shell. Also comes as the Air Attack without the shield. Both are listed among Giro's aero helmets, but for most climates they should be rideable on the street in three seasons even with the modest vents. Available in the spring of 2013 at $200 and $240 retail.

  • Giro Advantage 2: A 2007 design and a welcome addition to Giro's lineup, their first chrono time trial helmet meeting the US CPSC standard. (Giro's previous Advantage model had been sold only in Europe.) Molded in the shell with five small slit vents and the usual long chrono tail, open underneath. Retails for $165 but we have seen it discounted on the Web for as little as $100.

  • Giro Selector: Giro's newer chrono model with no front vents, small rear vents and a shorter tail. Giro says it accommodates new time trial positions and off center yaw better than the long tail models. There is a removable piece that attaches to to the bottom of the tail to extend it downward if that configuration is needed to close a gap to reach the rider's shoulders. It retails for $275 with face shield. Giro has other models sold in Europe for use where CEN helmets are required. Those may not meet the US CPSC standard.

  • Gray Aerodrome: Synergy Sport has one helmet in their Gray line for triathletes. It is molded in the shell with the long teardrop shape of the classic chrono, with six small slit vents in the front and partially recessed strap anchors. It has soft "wings" on the sides. Strap junctions do not hold well. It is CPSC certified and comes in one size. It retails for $150. Synergy Sport has a "Life Time Crash Replacement Warranty" and the consumer can return a crashed helmet for a free replacement.

  • GUB-Air: GUB Bike International is a Chinese company with a full line of bicycles and accessories. They distribute a number of brands, including their own GUB helmets. Their chrono model is a long tail helmet with small vents in front and top. It is molded in the shell and fits head sizes from 57 to 62 cm. We don't know their retail pricing.

  • Kask K.31 Chrono: Kask's first chrono is a long tailed model with a polycarbonate shell that has a smooth rubber edge. It is not molded in the shell, but is based on the Kask K.10 road helmet. The ring fit system fits sizes 53 to 61cm. It has an optional face shield. Kask says that the shape and internal pivots are designed "for riders who simply cannot get the back of their head down low whether due to inflexibility, shape of the back or just general movement." It has reflective trim as if it were going to be ridden on the street. Made in Italy. Retail is $350.
  • Kask TT-Bambino: new for 2013, a chrono helmet in the Casco style that is almost as round and smooth as any helmet in the world, with just a hint of oval in the shape. Molded in the shell with a thin shell. There is a face shield that completes the round profile. Thin "micro vents" with chanels underneath provide some air flow. Has a magnetic visor mount. Meets the CPSC standard for sale in the US. Retail is $500.

  • KED Zeitfahren: KED's chrono model comes in long and short versions. The short version is called the Track and looks like a regular bike helmet but is smooth-skinned with no vents except in the rear. The long version is the Time Trial and has a long tail extending to the rider's back and covering the vents. Both have CEN and CPSC certification.
  • LAS Chronometro: time-trial aero helmet with a polycarbonate shell, no front vents and an integrated clear partial front face shield. Very long tail to reach the rider's back, with a slight shoulder hump. Certified to both the CPSC and CEN standards. Ring fit for 54 to 61 cm (21.3 to 24.0 inches) heads. Retail is $240.
  • LAS CX2: a very round, smooth helmet with tiny rear vents and a face shield. For pursuit and time trial riding, this is the response to Casco's Warp with a shape that drops the long tail that most riders don't keep tucked against their back.
  • Lazer Wasp: new for 2013, a chrono-shaped helmet with a long tail and four narrow vents. Molded in the shell. The bulbous front and tapering, descending rear sections are emphasized in the Fluo Black neon and black model with rings that imitate a wasp. The name is less obvious in the plain black or plain white models, and Lazer says it stands for Watt Saving Performance. Detachable sections, since it fits so closely that the rider puts it on in sections with helmet first, then snapping on sides and adding the tail. Ring fit. Retail is $400.

  • Lazer Tardiz: originally named for Dr. Who's time machine, but the s at the end had to become a z. A chrono model with front vents and a unique water intake used to replenish an evaporative cooling system. Dual shell enables a dimpled rear section. Air taken in through the front vents is said by the Lazer catalog to exit the rear and push the helmet forward. The only chrono model we have seen with a women's graphic version, called the Ldy Tardiz.

  • Limar Speed Demon: introduced in 2009, a CPSC certified chrono molded in the shell with 6 long thin vents in the front and 9 elsewhere for a total of 15. Limar says they offer good ventilation "without affecting the aerodynamics." It has a flexible ear flap to avoid the chafing problem Ring fit for heads 54 to 61 cm. There is a carbon version, but that refers to the black color, not the shell material. Retail is $190.

  • Limar Chrono 05: an aerodynamic pursuit and time trial helmet with CPSC certification. Molded in the shell with 5 small vents in the rear recessed into channels. Face shield optional. Limar says the short shape permits more efficient bike position and works better when the rider is out of aero position or standing. Ring fit for heads 53 to 59 cm. Retails for $170.

  • Limar Superchrono: Limar's CEN-only chrono with ring fit system and a taped on shell has two large front vents. Not for the US market. Pricing is described as "affordable." We don't know if this one is in production any longer.

  • Louis Garneau P09: Louis Garneau was the first manufacturer to make a chrono helmet that passed the CPSC standard. This 2013 model continues that tradition, and represents the next generation of Louis Garneau chrono models. It has the traditional curved surfaces in front sweeping back to a short tail. There is one front vent, but it can be plugged. Garneau's marketing says they thinned the liner for a smaller front profile.

  • Louis Garneau Superleggera: The Superleggera is the 4th generation of Louis Garneau chrono helmets. It is dimpled like a golf ball in front for aerodynamics. Unlike most chrono helmets it has large vents--two in front and three in the rear. It has a medium long tail. The shell is glued to the liner, not molded. Garneau says the center of gravity has been adjusted to reduce neck fatigue and make it easier to maintain an aero position. It fits 52 to 62 cm heads. Retail is $180, with an additonal $45 for the Rocket Case and $35 for the windscreen. The same helmet is also known simply as the Chrono.

  • Louis Garneau Vorttice: Garneau's third generation 2011 design, dimpled in the front like the Superleggera, but adding a line of raised bumps across the crown that Garneau says will accelerate the air and cause it to flow smoothly down the sides in the rear. The Vortice has a single large rectangular vent in the front and a single air outlet in the rear. Meets the US CPSC standard. You can find it on Youtube. Retail is $250 to $260.

  • Louis Garneau Windscreen: Not a helmet, but an accessory, this is a polycarbonate lens that wraps around a helmet--almost any helmet--and is held on by hook and loop. It fits all of the LG chrono models. Comes in clear, smoked or contrast-enhancing yellow. The edges are unprotected except at the nose, and you could probably slice meat with them, even if it did not shatter in a crash. We would favor something with protected edges, like a pair of glasses or goggles. Retail is $35.

  • POC Tempor: introduced in 2012, a unique chrono model that flares out on the lower sides and has a long tail that fits snugly to the neck and rises to curve over the shoulders. The object is to treat the cyclist as one body mass rather than a separate head and body.



    Has two big vents in the front, and two small retangular vents in the rear, but there are hints that "the vents might not be what you think they are." Comes in neon orange, black and white. Retail is $380.

  • Rudy Project Wingspan TT: A chrono model with more vents than most, a face shield and a split tail. Molded in the shell. There are unique pieces on the sides that extend down to about the cheekbones, called "bionic wings." Medium length tail does not get all the way down to the shoulder, and is said to be designed to maintain aerodynamics for riders who sometimes look down or to the side. Comes with mesh or solid plugs for the front vents. Ring fit with one shell size to fit 54 to 59 cm (21.25 to 23.2 inch) heads. This is Erik Zabel's time trial helmet. Comes in red, white and blue as well as white. CPSC certification. Retails for $300.

  • Rudy Project Syton Supercomp: another chrono model with the split tail, but with small vents, no side pieces or face shield. Two shell sizes fit 54 to 62 cm (21.25 to 24.4 inch) heads. This one retails for $225.

  • Scott TTS: a long tailed model with three small vents in front and side pieces with vents in them. Molded in the shell. Meets only the CEN standard, so can't be used in races sanctioned by USA Cycling. Fits sizes 54 to 61 cm. (21.3 to 24.0 inches). Retail is 150 British pounds, about $230.

  • Scott Split-TT: a compact model with integrated face shield available in mid-2013. Flexible side pieces around the face to facilitate putting it on. No vent holes visible, but there are vent slots at the top of the face shield linking to internal channels and slits at the rear. The strap adjustors hold reasonably well. There is marketing background on the Scott site.

  • Selev Tempo: long tailed model with a full lower cover that comes all the way down to the neck. Vents, with some lines sculpted in the shell rather than a completely smooth profile. Certified only to the CEN standard, so can't be used in races sanctioned by USA Cycling. Has an internal radio wire channel. Fits sizes 54 to 59 cm. (21.6 to 23.2 inches).

  • Shain BK500: actually a road helmet with an additional fairing added on the exterior and a clear face shield. There are three small front vents, five total. Normal EPS foam with Shain's inner shell, weighing 350 gr. It retails for $197. Certified to the CEN standard, so can't be used in races sanctioned by USA Cycling. It has dropped out of Shain's catalog.

  • Specialized S-Works TT2: a long tail chrono model. Has one large brow vent in the front in Specialized style, and four large rear vents on the tail. The tail is open underneath. Has non-stretching straps. Two sizes fit 52 to 61 cm (20.5 to 24") heads. At present this is the only model certified to Snell's B-90TT helmet standard, permitting long tails but requiring a special warning label (see above). Retail is $250. Specialized has other chrono models not available through retail, and sometimes only CEN certified for European racing. They include the TT1, TT3 and TT4. The TT4 is new for 2013, with aerodynamics technology contributed by McLaren. It is a very expensive limited edition model with multiple very narrow "gill" vents on the sides that Specialized says improve the aerodynamics.



  • Spiuk Kronos: a time trial teardrop shape with two small front vents and a center rear vent through the long tail. Molded in the shell. Ring fit. Meets the US CPSC bicycle helmet standard. Retail is $235.

  • Uvex Factory Pilot 2: A classic chrono design with a long tail that lies flat on the riders back and is covered on the bottom. Has low sides, and a nicely integrated face shield. It has an Acoustic Warning System that hums when it is off-center to alert the rider to less-than-ideal aero performance. Weighs 280 g. Meets the European EN 1078 standard but not CPSC, so can't be used in races sanctioned by USA Cycling. Retails for $450. Look for it on the T-Mobile team. Kristen Anderson won gold for the US in this helmet at the 2008 Beijing Olympics, and Uvex did not pay her a promotional fee to wear their helmet.


    This page was last revised on: November 2, 2014.

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