Tuesday, January 22, 2013

Tuesday TT/Triathlon Post - AERO HELMETS

There are a lot of articles/blog posts out there that discuss the benefits of an aero cost versus the costs compared to an aero wheel set and other options at reducing drag on a TT/Triathlon Bicycle.

Today I am referencing a post from the website where I post all of my training and do a lot of my research through -

"What are the average time savings you can get from using an aero helmet?  I am pretty sure I know what it would be for the aero wheels but getting a wheelset is a ways off.  I was hoping I could see a significant time saving (over an OLY distance race) from just the helmet alone."

Answer by Dean Philips

Aero helmets typically save 30-60 seconds for every hour of riding. The actual time saved for a triathlete depends on how well the helmet smooths the airflow from the helmet to the middle of the back. This time can be broken down by race distance as:
  • Sprint triathlons – 15-30 seconds
  • Olympic distance triathlons – 30-60 seconds
  • Half Ironman Distance triathlons – 1.5 to 2.5 minutes
  • Ironman Distance triathlons – 3-5 minutes

You can spot a good helmet to back transition visually by looking at a rider from the side. In this first picture notice the large gap underneath the tail of the helmet. This will still be more aerodynamic than a traditional vented helmet, but ideally there would be a smaller gap under the tail of the helmet.

In the following photo the gap is smaller, and will be more aerodynamic. Many triathletes have aero helmets looking similar to this, but things can still be better.

This last photo shows an ideal aero helmet fit. There’s no visible space underneath the tail of the helmet. The tail of the helmet smoothly transitions to the middle point of his back. This creates a very aerodynamic profile that cuts down on the drag associated with the turbulent air flow and separation behind a regular helmet.

Are all aero helmets the same?

The fastest aero helmet tends to be different from person to person. While five years ago there were only a handful of aero helmets on the market, today most helmet manufacturers have at least one model and sometimes two or three to choose from. A good bike shop should be able to tell if one aero helmet ‘looks’ better than another on you. The speed at which you can get the helmet on your head may be more important if you only race short course triathlons. There are also helmets with ports on the top to pour water onto the top of your head while riding on hot days.

Overheating in an aero helmet

Will you overheat with an aero helmet on a hot day? The aero helmet will reduce ventilation to your head compared to a traditional helmet, but in our experience this rarely leads to overheating or a condition where you’d be better off with a vented helmet. If your goal is just to finish a long distance triathlon on a very hot day, then perhaps it’s better to go with the traditional helmet for maximum cooling effect possible. That being said, a number of aero helmets have small cooling vents in the front of them as well. It’s often overlooked that the rest of your body has a continuous 15-25mph fan blowing at it just from riding. The restricted cooling of your head tends to be quite small in comparison to the rest of your body.

Tips on positioning the aero helmet:

  • Tilt the helmet back more than you would a traditional helmet. This will allow the tail of the helmet to rest on the middle of your back or close to it. I like to feel the tip of the helmet touch my spine when I tilt my head back. The helmet will still be just as safe, but aerodynamics will improve.
  • Tucking your head where possible can further reduce your drag. This is particularly important for short course triathletes and time trialists where seconds are more important. Try pushing your chin toward your front wheel hub, while at the same time looking up the road. This will often lower your head several inches and lines up the tail of the helmet with the top of your back. The term “turtling” your head is often used to describe this position.
  • Avoid excessive movement of the head. An aero helmet can quickly lose its benefits when you look to the side or straight down and expose the big tail of helmet to the wind. If you find a head position where the helmet gets quieter, then that’s likely a good position to be in as it’s a sign there’s less turbulent air flow coming off the helmet.

Dean Phillips is a co-owner of Fit Werx²in Peabody, MA.  Dean frequently writes tech articles for and is humble enough that he would likely never tell you (so we'll tell you for him) just how fast he is on a bike.  Dean holds multiple TT course records in New England, having broken records previously held by some of America's best pro cyclists, and he set these while being a father of three young children and owning his own business.  Dean knows speed and how to get the most out of his training time.

If you want to come in and see the selection of aero helmets we carry at Tom's Pro Bike stop on by during regular business hours.

Tom's Pro Bike Service
3687 Walden Avenue
Lancaster, New York 14086
F: (716)651-0858

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