What we learnt using the "world's first real-time aerodynamic drag force measurement system for cyclists"

The prospect of measuring drag without a wind tunnel has been coming for quite some time now. In fact, we first reported on the Body Rocket system that its creators claim can do just that at the start of 2021. Real-time drag measurement is clearly a tough nut to crack, but with Body Rocket set to open pre-orders in the coming months, is it finally a reality? We were invited to trial the system to find out.

On most bike rides, both weight and rolling resistance pale into near-insignificance compared to aerodynamic drag. Being 'aero' isn't something that's just reserved for the pros, and should be a consideration for anyone looking for additional performance on the bike, whether that be to travel faster or simply more efficiently.

Unfortunately, even knowing your aerodynamic profile is easier said than done. Measuring your CdA (Coefficient of drag) is prohibitively expensive.

> Should you buy an aero road helmet?

For example, Silverstone Sports Engineering Hub is a popular choice in the UK, and yet will set you back around £400 per hour once a technician and VAT have been accounted for. 

What do we do then? Just take the manufacturer's aero claims as gospel? No, thank you! 

What is the Body Rocket System?

Body Rocket is a device which fits onto your bike in the form of sensors on your seat post, stem and pedals. It can then stream real-time aerodynamic drag force data to a Garmin head unit for analysis post-session.

The idea is that the device is used similarly to a power meter, in that it remains fitted to your bike for use during both training and races. According to Body Rocket, this will not only allow you to see how your position affects your CdA as you ride, but can also help to make "a comprehensive picture of your aerodynamic data which you can analyse to identify incremental improvements", such as when experimenting with different positions, movements and kit.

> Best aero road bikes

The system that we used utilised the AeroSensor airspeed sensor, although Body Rocket are trialling multiple options. I used the Aerosensor device earlier this year, and it also claims to be able to tell you your real-time CdA. How does Body Rocket differ?

Eric DeGolier, the CEO and founder of Body Rocket, says: “The alternative systems on the market use a method called Virtual Elevation which takes your power numbers and from there, you know how much energy you are putting out.

"It has to make some estimates about all the other energy losses in the system. That’s rolling resistance and drive train losses. It also assumes that your body weight stays constant, but this does vary over the course of a long event. Only when getting all those guesses right, what is left is your correct CdA.

“We [Body Rocket] are isolating the rider from the bike and looking at just the body."

> The future of going fast? Why live drag sensors might be cycling's next big tech craze

Body Rocket says this is how rolling resistance and drive train friction are completely removed from the equation, and has completed its testing in collaboration with the University of Southampton and its wind tunnel to determine the accuracy of its device.

DeGolier says: “As we are doing the same type of measurement, the actual direct measurement of force, this is the only type of device that you can take into a wind tunnel and measure directly against it.

> Why riders like you need to get more aero

"Other devices rely on back-calculating from a power measurement, and since power is entirely unrelated to wind speed in a wind tunnel all they can do is check to make sure their wind speed measurement equals the wind tunnel."

According to Body Rocket, their device is accurate to 2.5% over a range of different positions. 

Using the Body Rocket System

To get a better idea of what real-time drag measurement looks like, I headed off to Reading outdoor velodrome on a bleak Tuesday morning to have a play.

As it stands, Body Rocket is focusing on the launch of the system for time trial and triathlon bikes, but looking at this photo of Kristen Blummenfelt's Giant Propel (above) there is also a road bike version of the system in the works. Body Rocket was tight-lipped on when this might be ready for consumers.

> Kristian Blummenfelt puts ambitious plan to win Tour de France on hold

Rather than simply use the device to improve my horrendous TT position, I was keen to see whether the Body Rocket system could reliably measure the wattage saving when switching equipment. In this case, I selected a ventilated helmet and aero helmet.

You can read the full feature on whether you should buy an aero helmet and find out exactly how much faster one could make you by clicking here.

The test protocol was fairly simple, but if you need some guidance then Body Rocket's AI assistant BRIAiN will happily jump in to help. I rode for 10 minutes to set a baseline and then a further 10 minutes in each helmet, then repeated the test to see if I got the same results (spoiler alert: I did).

While riding the Garmin displayed my ever-changing CdA, so you can react to what the data is showing you in real-time. I can see this being useful in a time trial, where riders often neglect their position as they fatigue.

The Body Rocket system should allow riders to find their optimal position, that is sustainable for the event duration, and flag when they deviate from it. Just like riding to power, we could all be riding to CdA figures in the near future too!

Just like with a power meter the CdA figure does flicker around quite a lot as it's impacted by wind conditions yaw angles so it's better to look at an average, for example, I could see the average CdA for each lap of the velodrome. 

Although I haven't been to a wind tunnel to validate the results the numbers that the Body Rocket outputted certainly seem believable and fit with the wattage saving that we expected to find.

> Has aero gone too far? 

How far the CdA value that the Body Rocket system gave me is from the 'true' value I don't know, but after just a few hours of testing I was categorically able to determine that one piece of equipment was faster than another. For performance-minded cyclists and teams, this could be invaluable information. 

Post-session, I was greeted by a surprisingly easy-to-interpret Body Rocket dashboard. Here, I can see the CdA for each run as well as the wattage savings this equates to at the speed I was travelling.

Diving deeper, I can see how my weight was distributed on the bike. It's interesting stuff, and useful for determining whether it was an equipment change causing CdA variations rather than my position.

Using the dashboard I'm also able to see my pedalling metrics, similar to a Wattbike, and could see that I slowly crept forward on the saddle over long runs. This data could be very important to pro teams and athletes, and a perk of using Body Rocket over a wind tunnel.

> An air-filled cycling backpack to "reduce drag and "enhance safety" is about to hit Kickstarter

The Body Rocket team were keen to remind me that the system was very accurately measuring my weight at all times. I did kind of wonder why this was necessary, because I know how much I weigh!

It turns out that even on the shallow turns of the track I was around 2kg heavier in the corners than on the straights due to centripetal force. Professional track sprinters can weigh double when cornering on a velodrome, so it's easy to see how guestimating your weight could cause issues!

What I learnt (or was reminded of) using the Body Rocket system in handy bullet point form...

• Real-time, real-world aero testing is coming, and it's not far away at all!
• In my opinion, systems like Body Rocket could revolutionise how pro athletes and teams train/test products over the next few years
• Aero testing is still going to be prohibitively expensive, but we're heading in the right direction
• The Body Rocket system isn't just a replacement for a wind tunnel, it can be used in conjunction with one and/or even give additional data
• Amateur athletes should be looking at their body position A LOT more than they are before even considering buying more 'upgrades'
• The aero revolution is only just getting started!

Let us know what you think of aero measuring systems like Bodyrocket in the comments section below.