Aero Testing - My Windtunnel Findings
How to find watts.
I’ve promised this one for a while, took me a long time to write - sorry.
Aerodynamics make the cycling world go round - right? In the time trial world, it’s “watts per CdA” rather than “watts per kilogram” that dictate who wins.
Growing up on the British TT scene, I’d spend hours finickity-ing around with my set-up. Whether it be an extra bit of electrical tape here, or a slightly higher aerosock there. I’m definitely not a full blown aero-nerd a la Bigham or Disley, but I’m certainly an aero fanboy.
Twice this year, I headed to Silverstone Windtunnel in pursuit of time trial gains. The first was with my kit partner, Velotec with an R&D goal. The second time was searching for my own performance.
The Process:
Andy Turner of ATP Coaching ran my windtunnel session. Here, he explains what happens from the engineering/consultant perspective.
“The procedure for determining the testing protocol is fairly easy. At Silverstone there is software called Aero Data Centre (ADC) where we programme the testing map.
To do this I ask clients what events they are targeting and what the conditions are like. For example, testing a Team Pursuit rider going to the Olympics will require test speeds of 60-65-70kph at YAW angles of 0-5 degrees.
However, a time trialist on the road aiming for an 18min 10mile TT (or faster) would be tested at 45-50-55kph with a YAW of 0-5. Then, an Ironman athlete where crosswinds are more prevalent would be 40-45-50 kph and 0-5-10 degrees YAW. It all depends on the speed and conditions. The faster you travel the lower the YAW you experience, and certain events will have higher YAW angles - such as the KONA Ironman.
Different positions and products will be faster or slower at different speeds and YAW angles. Looking at the latest craze, aero base layers, some are optimised for speeds of 40-45kph, while others are better suited for 50-60kph. This is why it’s impossible to say that ‘A will be quicker than B as the reality is we can’t tell for certain without testing.
Inside the tunnel itself, it is fairly simple. Once the bike is on the jig, it’s a case of capturing a tare and edges to ensure that runs are calibrated correctly each time and we can see the differences in position using the edges. I personally keep the edges the same throughout as that shows a pattern of what has changed -it also shows position repeatability when testing different equipment. There’s no point testing two different skinsuits if you are changing the position between tests!”
Personally, I just sat there and looked pretty. I followed Andy’s lead.
My Position
Simply walking into a windtunnel doesn’t guarantee gains.
“When testing Joe, the first thing I noticed was that his shoulders flared out, so the first change we made was to tuck those in. Yet, when looking at the new position, this brought his head up a touch. Looking to the data, bringing in his shoulders made a bigger difference than tucking his head, so we stuck with it. At 50kph, this change made a difference of approximately 7 watts, or nearly 9 seconds over ten miles.
The next thing I noticed was his cleats . They were pretty wide apart, so we tested bringing those in. It gave a modest saving of 3 watts, but in practice Joe found this a little uncomfortable for longer durations. I suggested using this setup for short TTs as it would save a handful of seconds, but over longer events comfort needs to be a consideration as that will negatively impact power.”
The comfort vs. aero problem is a classic. It’s easy to go into the windtunnel and contort your body into this aero-foil while riding on a stationary jig. Yet, in practice that position is impossible to replicate safely on the road. You’ve got to be able to put power out too.
We looked at dropping the saddle and then moving it back a little too (moving saddle back reduces the overall height while maintaining leg extension but does decrease the hip angle). This made a nice saving of 5 watts, but it was horribly uncomfortable. I felt that I couldn’t really pedal at the 200w I was riding at, let alone the 400w+ I’d try to push in a 10. The saddle went back up.
Equipment Changes
“If you don’t test it’s just a guess” - Me, probably stolen from someone else.
I’ve lost count of how many times I’ve heard outrageous claims when it comes to cycling aero. It bugs me. After a couple of times in the tunnel, it makes you realise that when a brand claims something is X watts faster, it might not be the same for you.
The POC Tempor Aero Helmet is one of those products. For certain riders it performs amazingly well, for others it’s relatively slow. When Bigham brought it back into fashion, POC seemingly couldn’t supply them quickly. The thing is though, without testing whether it’s faster, you’re simply guessing.
For example, a Kask Mistral is a decent helmet for everyone. However, the POC Tempor seems to be so personal that if you haven’t tested it then it’s a waste of space (and money).
In my eyes the most interesting bit of tech we tested was the Kask Pro Visor as seen at the 2022 Tour de France Prologue. I didn’t know how this would test, and I think the results shocked us all.
For me, it was 0.4w faster at 45kph, 1.2w faster at 50kph, and a massive 9w faster at 55kph! This made sense as the visor was designed for the speeds that Ganna races at and shows why the speed that you race at is a consideration. However, don’t rush out to buy it, on the other rider I was testing on the day, that same visor was slower in all cases.
Skinsuit Changes:
“There is an individual nature of aerodynamics. What works on one rider at a given speed will not necessarily work on another.” - Andy Turner
A trip to the windtunnel can be great, it can also be frustrating. Frustration was the main take away of my R&D day with Velotec. We tested a lot of different skinsuits, and came away asking more questions than having answers.
The experience there showed that product development and improvements are not always a linear progression. Aero development seems to resemble more a game of snakes and ladders, where what you think in theory is aero has you sliding down a snake back to square one, only later to develop something else that has you climbing back up the ladder.
Everything we thought would be fast, was slow. Everything we thought would be slow was fast. At the end of the day, our baseline suit, the trustworthy PRO8 was still standing strong against any of the new suits or competitor suits. There were tiny tiny differences, but not enough to glean anything of interest.
The most interesting data that we found was that with my PRO8, which has textured material on the arms, adding an aero base layer made it SLOWER. On one hand, that isn’t a surprise. This PRO8 was not designed with a base layer in mind, and it seems the textured material + the base layer makes little difference.
It’s also a warning to be wary of certain marketing claims. Yes, for some suits adding a base layer will be faster. But, not all of the time. Blindly adding a base layer could be making you slower. For example, I was testing with a friend of mine. When he removed the aero base layer that was designed with the suit, he was 17w worst off.
On my second trip to the tunnel, we didn’t test any new skinsuits as that was my whole day out with Velotec. The only alteration we made was to stuff another skinsuit down the front of my PRO8. To everyone’s shock, this saved me an average of 7.8w over 45-55kph and 0-5deg yaw. That’s a lot of watts, but it wasn’t without controversy…
The full (somewhat surprising) Velotec data can be found here.
The Cost
Is the wind tunnel worth it? It’s one of those questions which people always ask as the cash investment is significant
While the first trip was part of a Velotec R&D session, my personal tunnel trip cost in excess of £600 for 90-minutes. That’s about £7.20 per minute, and doesn’t include my travel costs either.
When you brake down the £/watt saved, I do think it is a worthwhile investment if you’re at the pointy end, or chasing a certain target. However, there are plenty of other places that you can optimise before going to the tunnel.
Then there’s also the content side of it. It may sound stupid but apart of my job these days is producing content for the brands I worked with. Whether it be marketing content, or stuff for YouTube, my sponsors used the imagery we got from the day. In my opinion, that increases the ROI for me, and was potentially reflected when it came to contract renewal.
Conclusion
I’ve always been relatively slippy, but coming back to the British TT scene in the past year or two it has made me realise I’ve fallen a bit behind. My CdA hovers around the mid .19 mark. That’s good, but no way near good enough.
“It helps to look at the rider as a full picture when the total goal is to make them faster. Observing them on the bike and getting them to report back on how a position felt is very important and you can work out biomechanical limitations which help inform positional changes. Sometimes these limitations can be remedied through S&C work, but sometimes you have to work around them. For Joe we worked out several positional changes that would be faster, but they required a bit of work off the bike to make them genuinely faster in terms of being able to put the power out and making the watt saving aerodynamic changes.”
As Andy says, aerodynamics is a full-package. It’s equipment, position, testing, strength work. There are so many different dimensions to going fast on a TT bike. Then there’s riding the thing. Up until National 10 this year, I’d ridden my Ribble Ultra TT Bike less than five times. That was sub-par but just how it fell with me not building the bike until late in the year.
As Ken Ballhause, Founder of Sync Ergonomics, says: “Athletes need to get that TT bike off the trainer and learn how to ride it in the real world, at a pace that approximates racing. Back this up with skills sessions, especially in the lead-in to competition.”
Will I get back in the tunnel come 2024? Maybe. Hopefully. I want to take my Gravel bike in there too, but as always it’s budget dependant.
Project TAG, proudly partnering (both for my athletic and influencing ability) with…
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