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What difference can the right TT helmet make in the real world?

If you’re semi-serious about time trialling, you’ve probably already done the research. There is no shortage of sites out there that will tell you a TT helmet will save you 60 seconds over a road helmet for 40km. But what about pitting one TT helmet against another? And what of that time saving is theoretical versus practical?

This weekend, I tried to find out by back-to-back testing the Bell Javelin, HJC Adwatt and POC Tempor.

Testing the Bell Javelin (left) against the HJC Adwatt (center) and POC Tempor (right)
Bell Javelin HJC Adwatt and POC Tempor

I’ve been wearing the Bell Javelin (the all-black helmet in the photos) since at least 2016 (I had a very similar Giro Advantage way before that) when Matt Bottrill convinced me that the Kask Bambino was not a helmet for serious Time Trialists who were not subject to UCI rules on cockpit setup, saddle position etc.

And he wasn’t wrong. Switching to the Javelin definitely helped me get more aerodynamic, reaping the benefits of the interface between the long-tail helmet and my back.

Since then, aside from a very brief dalliance with a Giro Aerohead helmet, which really did not work for me at the time, I’ve worn nothing else, believing it was about as good a helmet as I could lay my hands on.

But with a poor start to 2021, I’ve come over all ‘bad workman blaming his tools’ and decided to try a few new bits of kit. Key amongst this have been two new helmets: the HJC Adwatt and the iconic POC Tempor.

Armed with these three helmets, I had to devise a way to pit them against one another in the hopes of determining which works best for me. The ‘for me’ part is really important. All I can do in this test is share with you my experiences. It is certain that other people will have different experiences, whether due to their bike setup, position, body shape or even potentially how fast they are (aerodynamics change at different speeds).

So, this is your buyer beware warning. If you copied my following test protocol exactly, it is very likely your results would be different to mine. Maybe only subtly different; maybe substantially so.

That done, let’s dive into things and start with a brief overview of the helmets on test.

Bell Javelin

The Bell Javelin is probably one of the oldest TT helmet designs you can buy on the market. The ones on sale today (circa £145) look exactly as my 5-6 year old version. But it’s a design that has a lot of fans, and rightly so. Essentially, it’s a teardrop long-tail helmet with an integrated visor (no fancy magnets or venting tech here) and the sides of the helmet extend down to cover your ears.

It’s a helmet that has tested very well with a wide range of riders for many years. It is, in many ways, a very safe choice.

HJC Adwatt

You’ll see the HJC Adwatt on the heads of pro riders from cycling teams like Israel Startup Nation and AG2R. It’s a short-tail compact helmet with a huge visor that wraps right around the front. It’s the helmet that Campenaerts wore for his hour world record ride, so it has form. The short tail should, in theory, make it a good choice for riders who can’t or don’t stay in a rigid tuck for the entire ride.

The HJC Adwatt will set you back about £270; a considerable amount more than the Javelin.

POC Tempor

Like the Bell Javelin, the POC Tempor has been around for years. It looked weird in 2014 and barely looks any less weird in 2021 (and even weirder with that duck paintjob from the TdF last year). Designed for the Danish track team, it has become an iconic design but not one you see too often on the amateur time trial scene. I think that’s probably down to three main factors: style, availability and price.

The style is marmite: you either love it or hate it and for some amateurs it’s just a little too ‘faux pro’. In terms of availability, it seems best to describe it as sporadic. Let’s just say there is a VERY healthy second-hand market for Tempors. And cost, well it’s an eye-watering £350 ish for a new one.

Like the Bell Javelin, it’s a long-tail design, but it has a much wider frontal area; the claims from POC citing that it’s the only helmet designed to actively channel air over the shoulders.

The testing protocol

Let me say upfront the testing protocol is imperfect, as any tests are when done outside on public roads. Winds change, cars pass you closer or further away, any roundabouts or junctions will be near-impossible to navigate exactly the same way for each run.

So, I did the best I could with each run consisting of two ‘sectors’: a Southwest to South bound dog leg segment of 3.93km with a left-turn at the roundabout about halfway and then the reverse course (3.88km) back to the North and then Northeast (same roundabout, right turn). Luckily none of the runs were significantly impacted by the roundabout or traffic.

The protocol was to test each helmet twice, so six runs total in this order: Javelin, Adwatt, Tempor (and repeat). The first set of runs were at a target power of 225 watts in each direction and the second set of runs were at 230 watts outbound and 240 watts return (I know that power is a little low but hey I had six runs to do and a race in 48 hours!). All runs were within two watts of average target power (although again, worth pointing out that doesn’t mean the powers were exactly the same at key points of each course – I’m not that good at measuring my power delivery!).

The (simplified) table of results (all taken from splits on my Garmin and using Favero pedal-based power meters) looks like this:

Note the table indicates whether there was a tailwind or headwind on each segment. This turned out to be more important in differentiating the helmets than I anticipated. According to Strava, there was a 10kmh wind out of the NNE for the duration of the ride (and this felt pretty accurate on the day).

Interpreting the results

In short, with a tailwind (the outbound segments) the Bell Javelin was the slowest by up to five seconds. Not a huge deal on a training ride, but over 16km instead of just shy of 4km that would be 20 seconds or so (assuming it was a tail wind all the way!).

When it came to the HJC Adwatt vs the POC Tempor, there was very little between them. At 225 watts, the HJC scored two seconds faster than the Tempor (but, being new to the Tempor I don’t think I had it sat quite right, so I am not 100% happy with that run). At 230 watts, they recorded exactly the same time on the outbound leg.

It was the return leg, into the headwind, where things got more interesting. Again, the Bell Javelin was slowest, although only marginally slower than the HJC Adwatt (two seconds at either 225 or 240 watts). The clear winner of both runs into the headwind was the POC Tempor – up to 11 seconds faster at 225 watts and a whopping 15 seconds faster at 240 watts.

Multiple that by four for a rough 10-mile course and you’re looking at a full minute faster.

Combining the outbound and return legs into a single figure (both legs were started at as close to 30kph as I could measure) and the results show up to a 20-second advantage for the POC Tempor.

Or, let’s pretend our course was twice as long but the same shape (Southwest to South on the outbound, North to Northeast on the return), we might expect to see the POC shave 36 seconds off the Bell Javelin and 26 seconds off the HJC Adwatt.

Pretty significant.

Now, like I said the test is imperfect and the margin for error has to be considerable. But we also have to again acknowledge that these are my results and yours would likely be different. I have not yet raced the POC in anger (I will tomorrow!), so the test is my one and only measure of that helmet.

Tester’s notes

The outright figures are what they are and they do seem to show some clear results. However, it’s perhaps worth adding a few notes about what it’s like to use the helmets in the real world; fit and visibility being two important considerations.

Having worn it for five years or more, the Bell Javelin now feels very familiar to me, but it has never had the best visibility through the relatively shallow visor and low brow. Like many, I added extra padding at the front of the helmet inner to try to create both a better position for aerodynamics and lift the visor relative to the eyes (allowing you to get your head lower while still being able to see the road ahead).

In terms of visibility, the HJC is on another level, with a truly massive visor and a high brow that allows the rider to adopt a significantly more ‘head down’ position while still being able to see the road ahead. It’s also arguably the comfiest helmet of the three although there is more air around the ears which sometimes makes you think the helmet is not as fast as it really is.

So far, I’ve struggled to get a comfortable fit on the POC, despite what the test figures suggest. It comes with different sets of padding to adjust the fit, but there’s little or no instructions on how / when to change the padding so at the moment I just have the default inner fitted. Getting the helmet sat on the head just right is a bit hit and miss (so far) and the way the visor attaches to the helmet shell (some kind of plastic bubble version of Velcro) is a faff and I lost the visor on the first run of the test (thankfully the van driver behind me saw it and avoided it, thank you!). The visor, like the Bell, is also pretty shallow.


In terms of outright speed, the POC does appear to work for me. As per my calculations, it’s worth in excess of 30 seconds in a ‘real world’ out and back 10-mile course with 50% tailwind and 50% headwind. But that 36 seconds will cost you £200 (the Bell Javelin is around £150 versus £350 for the POC Tempor).

In the world of time trials that’s actually not a bad deal. I’ve seen people splash a lot more cash on ceramic BBs or jockey wheels, and the Endura Encapsulator skinsuit (yeah, I got one, review coming soon) is £400 compared to Velotec’s £190 skinsuit (and I’ll bet there isn’t 30 seconds difference between those two suits at 45kph).

Parting words of wisdom?Well, the Bell Javelin is not a slow helmet. I suspect it still offers a substantial advantage over a road helmet.The HJC is a great all-rounder; comfortable to wear, substantially better visibility than either the Bell or the POC. But if you want to maximize your speed into a strong headwind, my limited test would suggest the POC is the way to go.If you can bear the price and the strange looks.


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