Gain without pain - here’s the cost-free aero test that every cyclist should try

If someone told me they could add 10 watts to my threshold power in an afternoon, I’d bite their hand off. To add this much power through training alone would take at least a few solid interval sessions, if not several weeks of consistent hard work. But this is the promise of the simplest form of aerodynamic testing: a few pain-free test runs, a little positional rejig, et voila – a substantial dollop of extra speed. 

One day, no training, 10W faster – an amount of power that equates to almost one minute in a 25-mile time trial at around 40kph (25mph). To many uninitiated riders, it sounds too good to be true. But it really does work: there are ways to make yourself and your bike more aero without spending money.

If you can improve your position on the bike to minimise your frontal profile – the bits of you pushing against the air – and improve the way that air passes over you, hey presto, you go faster. Much faster.

Why slog away on the turbo, session after session, if you can simply tuck in your head and pull in your shoulders to make just as big an improvement to your race speed? OK, so it’s not quite that simple… 

To measure your aerodynamic efficiency, you need to ascertain your drag coefficient (CdA). The ‘Cd’ part refers to your coefficient of drag – basically your slipperiness through the air – while the ‘A’ refers to your frontal area. Multiplied together, these values tell us how much of our energy is being wasted on the wind. A decent CdA on a road bike is anything under 0.3m^2. However, measuring your CdA accurately requires wind tunnel testing, which for most of us is prohibitively expensive. So how can we improve our CdA by affordable means?

The good news is, it’s possible to estimate your CdA by using a power meter and other basic equipment. All you need to do is head down to a smooth stretch of road – ideally your local racing circuit or track, if you have access – with your bike and a power meter. Provided you know how much energy you are putting into the system, you can figure out roughly how much of that energy is being lost to air resistance. Though this is significantly less accurate than wind tunnel testing, it’s accessible to practically everyone. 

Even better news: there are apps that can help. Among cycling’s best free apps are BestBikeSplit and MyWindsock which estimate the CdA of a rider based on ride data and the conditions of the day, including air pressure, temperature, wind speed and wind direction (sourced from the nearest weather station). Provided conditions remain stable during your testing, there won’t be too many variables skewing your results, so try to pick a settled day and aim to complete multiple runs before the wind changes. 

Circuit testing

To put the theory to the test, we went to Castle Combe race circuit, in Wiltshire in England, with a test guinea pig, amateur racer Grace Reynolds. The 21-year-old is rebuilding her fitness after sustaining serious injuries in March when she was hit by a car while training. Reynolds put herself forward in the hope that labour-saving aero gains would help fast-track her back up to speed.

We set out to keep the testing procedure as simple as possible: having taken out a free trial of the full version of the MyWindsock app, our first run produced an estimated CdA of 0.220. Next, we tweaked Reynolds’s position and did another run – and then repeated this process 12 times in total (four times for each new position). The first positional change involved getting Reynolds to tuck in her head a little lower, and over several runs her new estimated CdA (as an average) was 0.218. 

As a further improvement, we shifted Reynolds’s hands up toward her face by moving the clamp around her bike’s base bar by 5°. The aim was to reduce Reynolds’s frontal area, and as an added benefit, many riders find that having higher hands improves comfort on the bike too. This led to a further reduction in estimated CdA to 0.209. 

The overall improvement, from 0.220 down to 0.209, is equivalent to saving approximately eight watts at 40kph (approximately 25-mile TT speed for Reynolds). This represents a 53 to 58-second gain over 25 miles for Reynolds, equivalent to boosting her power by 4.6%. To gain this much power from training alone would take Reynolds at least six weeks, even on her current steep comeback trajectory. Bear in mind too that such a gain from six weeks of training would not be permanent; it would have to be maintained through hard, consistent effort. 

Leaving gains on the table

The key takeaway from our testing is that, if you’ve been training for a while and feel like you’re stuck in a training rut (power gains are no longer coming thick or fast), you may be better off targeting your aerodynamics. Reynolds was blown away by how much we achieved from the single test session: “I’d been giving away almost a minute for free!” she commented. “For me, still coming back from the crash and not yet back to training fully, this has been a major mental boost too.” 

It’s important not to oversimplify. The improvements in position will only benefit Reynolds if she is able to hold that position for the full duration of a race. Her next step would be to focus on holding the new position for prolonged periods during training, and if necessary adding in core exercises and flexibility work to make this possible. Since our testing, Reynolds has completed a 200km training ride at an average speed of 33.2kph – very positive progress! 

Aerodynamic testing isn’t just for time triallists like Reynolds. If you tune into any professional road race, you’ll see riders wearing aero socks, skinsuits and aero road helmets, which is a marked change from just a few years ago. A few simple changes to your body position on your road bike can do wonders too, often saving upwards of 10W at 30kph. To put it bluntly, aerodynamics should be a preoccupation for anyone who wants to ride a bike fast, whether that’s in a race, sportive or just trying to win the cafe sprint. 

If money is no object, you can go the whole hog and get wind-tunnel tested for about £900 –expensive, but you can expect to save 20-45W and test tiny changes with spot-on precision. A middle way between our simple outdoor protocol and wind tunnel testing is an outdoor velodrome session with a specialist such as Aerocoach. This costs around £400 and many riders save in the region of 15- 25W. You can see why WorldTour teams are willing to spend big.

Bike-fitter’s advice: How to make aero gains last

Calum Hughes of bike-fit provider Veloclinic gives his top tips on making aero changes sustainable over the long term.

Start small: When adapting or adjusting to a position, make small changes, one at a time – movements of 5mm or less. Get used to it over two to four weeks before making further changes.

Check your breathing: If your breathing rate for the same power/ heart rate has become faster, it probably means the position change has made you less efficient as your body is demanding more oxygen for the same effort. 

Preserve movement: If you aren’t mobile in your new position, it might look good but can you still pedal at full power? The best position is about getting the balance right between power and aerodynamics.

See your way clear: If training indoors, place an object in the line of vision you will need to maintain while riding on the road. This will help to make sure your position works effectively without compromising your safety.

Next-level consumer tech

Even more exciting technological solutions may be on the way very soon. Aero sensors are being developed that, in theory at least, will be able to take drag readings directly from a rider’s body. One such system, being developed by a start-up called Bodyrocket, is attracting praise from aero boffins including CW’s own Michael Hutchinson. “The thing that is interesting to me,” Dr Hutch told me, “is that, because it’s only measuring the rider, you immediately factor-out all of the things that make aero testing in the real world difficult.” 

These sensors are likely to cost big bucks, but even so, they will inevitably be cheaper than wind-tunnel testing. Chris Hoy and Alex Dowsett are among the early investors – a positive sign if ever there was one. If these systems work, assessing our aero efficiency could become a simple test that we incorporate into our weekly cycling training plans, and the potential for major performance gains barely needs spelling out. Imagine being able to read your realtime CdA from the best cycling computers – these are exciting times. 

This is a well known fact but it warrants repeating: at normal, everyday riding speeds, around 80% of the power you produce is spent overcoming aerodynamic drag. Which poses the question: why slog your guts out training hard if you’re letting the wind rob you of 20, 30 or even 40 watts? Whether you opt for no-frills testing as we did or blow the budget on a trip to the wind tunnel, for most riders, aero testing reaps game changing gains. 

Money buys you accuracy, but basic trial-and-error testing is at least worth a few hours of experimentation. Reynolds is confident that our testing has kickstarted her comeback, despite the fact we made only small adjustments – a tiny investment of time with a significant pay-off in speed. It’s not too good to be true – you really can gain without pain.