I few years ago I heard John Cobb say that when he tested aero helmets in the wind tunnel it didn’t matter if the rider’s head was up or down. That always struck me as strange. When looking down the long tail of an aero helmet sticks up into the wind and would seem to add a fair amount of drag thus slowing the rider. A couple of weeks ago I got the opportunity to test helmets (and other gear) in the wind tunnel in Ft. Collins, Colorado with the guys from PowerTri, an online triathlon store with a retail outlet shop in Lehi, Utah. And now I understand what John was saying and why he was right.
The first picture here shows a common head position for athletes when racing in a time trial or triathlon. The second picture is the head-down position I mentioned above. I see this a lot at races. It seems riders want to frequently look at their gears or are continually resting their necks. Notice the helmet tail pointing up nearly vertically. What we found out was that the key here is not the tail of the helmet, which is small, but the position of the head, which is relatively large.
In picture 1 most of the rider’s head sticks up above the shoulders. This increases drag. In picture 2 the head is completely below the shoulders. This decreases drag. In fact, drag with the head down – even with the helmet tail sticking up – is significantly less than with the head in the common position of picture 1. The rider is more aerodynamic.
The PowerTri people checked the drag characteristics of several helmets that day both in the common and head-down positions. On average for all of the helmets there was a 1.4% decrease in drag when the head was down compared with the common position. That amounts to about a 51-second time saving in a 1-hour race.
Notice the third picture here. This is what might be called the “optimal” position. I wrote about this position last February following my trip to the A2 wind tunnel in Mooresville, North Carolina. You can also see pictures of the common an optimal positions in that post. The optimal position, compared with the average of all of the head-up positions, decreased drag by 1.5%. That’s a time savings of about 56 seconds in a 1-hour race – right in the same time range as head down.
I would certainly not recommend racing in the head-down position of picture 2 due to the inability to see where you’re going. It’s just not safe. A friend of mine once ran into the back of vehicle riding in this position in 1987 and has been in a wheelchair ever since. While it’s not safe for extended periods, an occasional glance down is apparently not going to slow you down, and, in fact, might even make you slightly faster. But, again, be cautious with taking your eyes off of the road ahead even for a few seconds. It’s quite risky.
On the other hand, tucking your head down between and lower than your shoulders may even be faster than looking down. And you can still see where you are going but it requires rolling your eyeballs up to the tops of their sockets as if peering over the tops of your sunglasses. This sometimes referred to as the “turtle” position. The challenge here is holding this position for long races. If you’re unable to do that the times when you can get the greatest gain from such a position is when you are going the fastest as on a downhill section of road or riding into a strong head wind. Tucking your head down like a turtle at these times will reduce drag when it is potentially the greatest.