So first, what is a TT helmet and why would you buy one. A TT helmet is one of those funny looking helmets that you often see used in track cycling, or you will see on the time trial leg of the Tour de France (hence the name). They usually look like something from the set of a Star Wars movie and I think most people would agree that almost nobody looks good in one.
So why would you bother wearing one. One simple reason really, they have significantly less drag than a normal helmet. In fact a comparison that is regularly quoted on the internet found that a TT helmet is one of the most cost effective ways of reducing your drag. In terms of drag reduction per dollar spent a TT helmet is much better value than something like race wheels, one of the best in fact.
If that is the case, then why wouldn't you wear one (other than not wanting to look like an idiot)? Well, most TT helmets incorporate all sorts of nifty features, but the basic way that they reduce drag isn't particularly complicated. They have less vents on them. In fact the ones that tend to have the lowest drag figures tend to be the ones with the fewest vents and usually a visor too. Fewer opening in a helmet means less drag, but it also means less cooling to your head. Overheating during a race is usually considered to be a bad idea.
The above statement has been changing a bit recently as manufactures increasingly realise that TT helmets for triathlon can't always get away with zero cooling. With this you are seeing helmets incorporating more features aimed at keeping drag low but still providing some cooling. Helmets that create a venturi effect around the visor, helmets with removable plugs to increase/decrease ventilation etc. Most of these features work reasonably well, but it is still fair to say that the most aerodynamic helmets also tend to be the warmest.
TT helmets also have other features to help reduce the drag. That is what the tail is all about. The idea of the tail is that it helps smooth the airflow off the back of the helmet and then down your back. This results in less turbulence at the back of the helmet and therefore less drag. If you ever want to feel this in action, then ride in your TT helmet without a shirt on (probably not recommended for the ladies out there). You should feel the air flowing off the back of the helmet and hit your back. It is kind of cool to feel the science in action.
In more recent times, developments with things like truncated aerofoils have shown that you don't really need the full tail to get the aero benefits of a full tail. This means we are seeing more and more helmets with short tails. We are also starting to see aero helmets with no tail at all. There is a pretty simple reason for this. A tail works great when you are looking straight ahead, but when you turn your head to one side, it is less of a tail and more of a sail. That is why in track cycling events where the cyclists spend a lot of time looking behind themselves they don't wear helmets with tails.
In triathlon we tend to spend a bit of time looking around. Sometimes we are getting drinks, sometimes we are looking at speedos, perhaps we are looking behind, maybe we are looking down to quietly cry to ourselves... Whatever the reason we are often not looking straight ahead. During these times the tail of an aero helmet is in the wind. There are a few designs that claim to reduce the amount of drag caused by the tail in these situations (my old Lazer Tardiz was one that claimed this). But I think manufacturers have started to think that the best way to avoid the drag caused by the tail, is to either have a short tail, or no tail at all. The logic being that the aero benefit of the tail is cancelled out by the extra drag caused by the tail when you aren't looking straight ahead. Most testing I have seen seems to back this theory up. As an example the Kask Bambino often wins real world aerodynamic tests. It wins the tests because it is quite aero when you are in the tuck position, but also quite aero when you are not. This is a helmet with a very short tail, a visor and almost no vents. Simple.
So moving on from that and going back to my original point, in triathlon the main way an aero helmet makes itself aero is by having less vents. The tail thing is less crucial. Tails certainly do help, but only if you are maintaining a good head position most of the time. Having said that, the helmet I have now has a truncated tail. Why? Well I think it strikes a good compromise between aero benefit when in the aero tuck and not too much penalty when I am not. On top of that I think it looks really good. They are also easier to pack than the full tail versions.
So what should you look for in an aero helmet?
Well firstly, one that fits.
Manufacturers don't tend to make a wide range of aero helmets. They usually just make one type, perhaps two. Within that range they will either make one, one size fits all helmet, or perhaps two sizes of helmets. If you have an unusually big head, or an unusually small one, just check that the helmet you are looking at will actually fit you (particularly if buying online). For example I know that Rudy Project make only one size of their popular Wingspan aero helmet, one size fits all. However, for me that size is too small (I have a big head). Kask is similar with their Bambino. When I was getting my most recent helmet the Bambino was my first choice since it comes out on top in a lot of tests. Only one problem, if I had bought one it wouldn't have fit me.
It just pays to check, in order to avoid disappointment.
What else beyond buying a helmet that fits? Hmmm, well the whole aero helmet thing is a bit of a compromise. The more vents, the more drag, but the more cooling. I guess the trick is finding one that provides the compromise you are happy with. As I mentioned above some manufacturers do some clever things with keeping their helmets cool(ish) without filling them with holes. My old Lazer had a hole for pouring water in the top, which actually worked. Lots of helmets now advertise that their helmet channels enough air in around the face so that they don't need extra vents. I have no idea whether they all work, but it sounds great idea. My current Lazer Wasp Air promises something similar, sucking air in around the visor. It does work, but within reason. I still wouldn't wear it in a very hot race, or I would wear it without the visor. Have a read of the advertising material from the various helmet manufacturers (take it with a pinch of salt) and see what they are proposing, find one that you think will work for you.
When you are looking at helmets keep in mind that some aero helmets are primarily designed for cyclists doing TTs. Generally cycling TTs are shorter than a long triathlon and they certainly don't have a run leg at the end. So TT cyclists can get away with less ventilation. The message here is that not all TT helmets are designed with triathlon in mind. Try finding one that is, they do exist and are becoming increasingly common.
When you are looking at helmets, take a very hefty dose of scepticism with you when you are reading the manufacturers claims. In the end what makes an aero helmet aero is pretty simple. However, the various manufacturers need to find something to differentiate themselves, so they will chuck around some interesting claims and 'revolutionary' developments. Most helmet manufactures will produce data 'proving' their helmets are the quickest. You wouldn't buy the third fastest helmet on the market after all. This data is often quite selective and at best can be a useful guide, at worst it can be entirely misleading. I wouldn't recommend basing a buying decision on manufactures claims alone. I have seen one manufacturer put dimples on the front of their helmet to supposedly reduce drag. I have seen another manufacturer put dimples on the tail of a helmet for the same reason. You will find all sort of impressive looking terms like boundary layer trips, usually with funky computer generated drag models to accompany them. In the end, find a helmet that fits, is a price you are willing to pay, won't cook your head and looks as good as it can. Whatever features it has beyond that probably don't matter too much.
Also, keep in mind that a lot of professional triathletes are given their gear. Just because such and such wears it, it doesn't necessarily make it good or bad, or the best helmet for you. It does pay to do a little research of your own when it comes to things like this.
One final point, and this goes back to TT helmets that are primarily designed for cyclists. Some can be a bit of a pain to get on. Cyclists have all the time in the world to get a helmet on, and off. They aren't trying to rush through T1 and T2 as quickly as possible. So my last tip would be to find a helmet that you can get on and off your head (and over your ears, since most of the helmets cover them) easily. This is doubly important if the helmet has a visor. If it is going to take you a minute to shimmy the helmet over your noggin in T1, or remove your ears when you rip it off in T2, then it probably isn't worth the effort. The easiest way to figure this out is to try it on first. If you are buying online, then good luck, online forums and reviews are probably your best bet.
One final, final point, even if you find a helmet that is the holy grail in terms of both aerodynamics and cooling, some days it may just be too hot to wear it. I know some coaches who think that TT helmets cause overheating in nearly all conditions and recommend that their athletes don't wear them. I am yet to ride on a day when I really felt like I was overheating (I have worn a TT helmet in 40 degrees and survived), but I have got close (looking at you Bintan). I have also ridden on days when I chose not to wear it. On days when it really is just too hot, then you are best to go without and stick to your good old normal ventilated helmet. Heat exhaustion is going to cost you way more time than an aero helmet can save. In the end there is a reason lots of people aren't wearing aero helmets in the photos you see of Kona.
In fact if you do mostly hot races, have a think about whether a full TT helmet is the best choice for you or whether you would be better off with an aero road helmet. These are a relatively recent innovation, but they promise a lot of aero benefit, but with more ventilation. I use one for particularly hot races up in Asia and I find that in those conditions they are a good compromise.
So in summary:
- Choose a helmet that fits
- Choose one that is the best compromise between cooling and aerodynamics for you
- Don't believe all the advertising material you read
- Choose a helmet that you can get on and off reasonably easily
- If it is really, really hot, don't wear it.
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