The Physics of Aerodynamic DragAerodynamic drag occurs when air resistance slows down a moving object. The faster the cyclist goes, the greater the aerodynamic drag. Drag force depends on the speed, surface area and drag coefficient of the cyclist and bicycle. The surface area and drag coefficient are often displayed together using the term CdA. Cyclists can reduce drag by minimizing frontal surface area and optimizing their body position. The best methods to achieve an aerodynamically efficient position are to test in a wind tunnel or velodrome however equipment such as the Notio Aerometer offer great alternatives and the ability to test yourself.
How Velocity Impacts Drag in CyclingAerodynamic drag increases exponentially with velocity. This means small reductions in drag have more impact at higher speeds. For example, a 10% decrease in drag could improve a cyclist's 40kmh time trial speed by 1 minute, but only improve their 20kmh speed by 15 seconds. Aero gains matter most when going fast!
Aero Cycling Kit
Most of your aero drag comes from your body. Whilst you will see the most significant reduction in drag by optimising your riding position, the difference your clothing makes could be well over 100 Watts for some riders. Optimising your aero clothing is significantly more cost effective than than upgrading your wheels or bike. A pair of aero socks can provide the same aero savings as a top-of-the-line wheel set for 1% of the cost. When it comes to kit choice, it's a common misconception that very tight kit is optimal - this is not true. Pulling fabrics too tight increases their surface roughness and their aero drag. You want a well-fitting suit that is tight enough to avoid wrinkles but no more than that.
Aero Bike DesignWhile your body shape are the major contributors to how much drag you will encounter, your equipment plays a major role too, aero profiled wheels, internal cable routing and minimal use of bar tape can all help minimize drag. Even something like the tread pattern on tires and how they blend into the profile of the rim play important roles in decreasing aerodynamic losses.
Optimizing Rider Position
For road bikes, in general, getting low and narrow on the bike improves your aerodynamics. Riding on the hoods with forearms parralel to the ground is more efficient than riding with straight arms on the drops. Tucking your elbows in tight, shrugging your shoulders to make them narrower and tucking your head into the frontal profile of your body. These are all free 'upgrades' you can make with some time and effort. An aggressive riding position may for a while be less mechanically efficient. You may notice a drop in your pwer output but with time this will return. Even if you do see a slight decrease in what you're able to produce, remember that in most scenarios it isn't your total power output that will determine how fast you can go, its your W/CdA.
Whilst the generalities discussed above are great starting points, to really dial in your riding position aero testing is the only way to go. Wether it's on a velodrome or in a wind tunnel, you will be able to quantify just how well a position or piece of equipment works for you. There is no one position or product that will work best for every rider so testing how they perform on you can be some of the best investment you can make in your overall performance.