Power, measured in watts, has become a popular and fundamental metric in cycling. For competitive cyclists, more power means faster speeds and longer distances. For cycling enthusiasts, more power means better physical fitness, smarter riding and honest measurement of calories burned.
Cyclists are now becoming aware and more involved in the next frontier of cycling performance improvement: aerodynamics. A measurement called "CdA" (coefficient of drag times frontal surface area) quantifies how "aero" the cyclist is. Simply put, the lower your CdA, the more aero you are. And watt-for-watt, the more aero you are, the faster you will go.
In fact, improving your aerodynamics helps you ride faster—without having to pedal any harder.
Of course, aerodynamics is a well-known part of achieving maximum cycling performance. Wind tunnels and velodromes are the venues where elite cyclists have spent thousands of dollars and many hours testing and quantifying the aerodynamic CdA of ride position, bicycle equipment and more.
The value of CdA can be as low as 0.15, a time trial cyclist who has the best gear and the best ride position, and as high as 0.60, which is basically riding upright on a commuter bike. The higher your CdA number, the less aerodynamic you are and the more effort it takes to fight the wind.
What influences CdA? Ride position, bike clothing, shoes, wheels and other bike accessories all factor into your CdA. Of course, the size of your body is important, too.
Ride Position And CdA
Ride position has a large effect on aerodynamic CdA. Imagine your body as a sail that catches the wind, the larger the frontal surface area (the “A” in CdA) your body “sail” presents to the wind, the more wind your body will catch. The more wind your body catches, the more resistive the wind will feel.
Moving your body from an upright, commuter-cyclist position, to a streamlined time trial position reduces the frontal surface area. The lower “A” is, the less wind you’ll catch, the less force wind will exert on you, and the faster you’ll travel.
Drag Coefficient And CdA
Not just the magnitude of the surface area is important, but shape of the surface is important too. Designing the shape of a bike surface so that wind moves smoothly around it reduces the drag coefficient (“Cd” in CdA) of the surface. Aero-shaped handlebars, TT helmets and deep-dish wheels are just some examples of special surface shapes that reduce the drag coefficient Cd.
Shape and Size Together Determine Aerodynamic Performance
The combined aerodynamic influence of shape (Cd) and size (A) is expressed by a single number: CdA.
A cyclist can reduce CdA by riding in a more tucked ride position (which primarily reduces “A”) and also by using better bike equipment (Cd: a skin suit is one example). Winning cyclists are known for doing both of these things, in addition to doing a lot of other things.
Let’s explore what happens to CdA when the cyclist changes ride position. The CdA of an average-sized cyclist riding on the hoods is commonly between 0.35 and 0.41. When the rider stands up, the body catches more of the wind and CdA goes up, often to a number over 0.45.
What does that increased CdA mean in terms of effort? Assuming the cyclist is traveling on the flats, when standing it will take about 25 percent more watts to hold the same speed.
Of course, the most common place where cyclists stand is on steep hills. Though CdA does go way up when standing up on hills, bike and wind speed both go down considerably. When going from the flats to a steep hill, if bike speed is cut in half climbing the hill, the watts required to overcome wind resistance are generally reduced by eight times. So yes, the rider does pay a CdA penalty for standing up, but low bike and wind speeds keep the watts penalty to a minimum.
Let’s think now about dropping from the hoods into a time trial position. In the TT position, there is less surface area to catch the wind. Furthermore, the rider may also curve his body and maybe place his elbows in a different position to reduce drag. These time-trial changes are reflected in a CdA that might drop to 0.25 or lower. The lower CdA number means that it is easier to ride against the wind. If you move from the hoods to a TT position and keep the same power output, you'll go faster: maybe even 10 percent faster.
The Aerodynamic Effect of Equipment
Clearly, ride position is important, but there are lots of other things that affect CdA: clothing, wheels, bike helmet, arm position and seat height are just a few.
QUIZ: WHICH BIKE COMPONENT CAN PRODUCE THE MOST DRAMATIC IMPROVEMENT IN AERODYNAMICS? (Read on to learn the answer!)
a. Deep-dish wheels
b. Aero helmet
c. Tight-fitting jersey and shorts
d. Aero-shaped handlebars
f. Aero-shaped carbon frame
The goal of “aero-designed” bike gear is to a) make wind move smoothly around the gear and b) to reduce the surface area exposed to the wind.
Cyclists can spend a lot of money on “aero” gear but here's the thing: everything you do to reduce your CdA makes it easier to ride against the wind. Being more aero helps you go faster, which is why you’ll need to start paying attention to your CdA.
How to Use AeroPod in Your Training Program
AeroPod helps improve your cycling in the short term and keeps you riding better over the long term.
1) Quantify where you are today—your baseline CdA.
The first step in using AeroPod is to establish your “baseline” CdA. You probably have a preferred training bike, gear and ride position. After a few miles of riding on your roads, AeroPod will measure your baseline a CdA number. This is the “starting point” for becoming more aero.
2) Discover the ride position that keeps your power up and your CdA down
One of the “dirty secrets” of wind tunnel testing is that the ride position that makes you the most aero is NOT always the ride position that makes you fastest. Why? Because in some (extreme) aero positions, your legs and lungs can’t function optimally: you lose power and you end up going slower!
When you change ride position AeroPod’s “real-time-CdA” reports the aerodynamic impact of those changes, but because you’re riding on your actual roads, you’ll also be able to monitor your real-world power output. The result: you can find the ride position that makes you fastest: the ride position that is the most aero AND the most powerful.
3) Find the best equipment for you and your bike
There are many aero-designed products out there. Which are best for you? Which ones will reduce your CdA the most? Which should you buy first? Here’s the answer to our quiz: clothing is a GREAT place to look for meaningful improvements in CdA, without spending a fortune to get those improvements.
If you have a friendly bike shop, use AeroPod to test and compare aero helmets, wheels and more. You might be surprised to find that some things that look aero don’t “deliver” as much as they seem to promise, and that other accessories are much more beneficial than you think.
4) Consistent riding style
Once you’ve got your ride position and aero equipment “nailed,” it’s time to take advantage of your aero position and equipment in your training and racing. We all have good and bad cycling habits and when you ride with AeroPod, you’ll see your CdA reported-out constantly. If you wander away from your optimum ride position AeroPod will let you know. You will see if your CdA shifts as you climb hills or go into a downhill aero-tuck.
5) After-the-ride analysis
Seeing CdA numbers on the road in real-time is great but analyzing aerodynamic data after the ride is just as important. Isaac software included with AeroPod has exclusive, "Analyze CdA" tools that allow you to do things like:
- Quantify the CdA aerodynamics of different kinds of equipment
- Change ride positions and analyze, post-ride, the CdA and Time Advantage benefit
- Analyze race results to see where you are more, or less, aero
Isaac CdA post-ride analysis is possible because AeroPod records, second-by-second, the raw sensor data from your AeroPod and DFPM.
But why should better aerodynamics and CdA measurement be accessible to elite/wealthy cyclists only? What's needed is an affordable, practical way to measure CdA.
Velocomp's revolutionary $499 MSRP AeroPod is the answer. AeroPod is the first (and only) device that can measure cycling power AND aerodynamic CdA, on your normal bike routes.
Aerodynamics measurement is the next “big thing” in cycling. AeroPod makes it practical and affordable for cyclists to quantify the aerodynamic effect of ride position and equipment, to find better ways to be aero and to produce high power output and to maintain “aero discipline” when training and racing.
This content is sponsored by Velocomp LLC.