By Rick Schultz, MBA, DBA
A question came in recently asking, “Which is better, more aero or less weight?”
I started thinking about this, since so many cyclists are more concerned with weight, especially here in Southern California. Just go to one of our local criterium races and you will hear the local racers talking about the weight of their new bike.
“Hey John, I just got this new and it only weighs 14.877 pounds.” “Bill, my new [insert manufacturer and model here] bike only weighs 14.587 pounds.”
Looking at the aero versus weight question as a coach, it’s obvious to me that aerodynamics is more important than weight. So then why do all cyclists compete for bragging rights as to who has the lightest bicycle? Shouldn’t it be who has the fastest bicycle, or, more accurately, who is the fastest by being the most efficient?
Let’s look at why aerodynamics are so important in more detail.
Two Parts of Aerodynamic Drag
There are two main categories to consider for aerodynamic drag.
- Rider – 75%-80% of aerodynamic drag
- Bicycle – 20%-25% of aerodynamic drag
First, size matters. A larger rider will always produce more aerodynamic drag than a smaller rider, so it is more important for a larger rider to get as efficiently positioned on the bicycle as possible.
Second, to get as aero as possible you will want to get your body as low as possible. Look at the frontal surface areas of the rider in red. Holding the tops of the bars generates the largest frontal surface area. Riding in the hoods is a little better and riding in the drops produces the smallest frontal area. A rider who is more flexible can get lower in the front by bending their elbows and rotating hips forward.
Third, consider your clothing. Loose and flappy clothing will cause a large amount of aerodynamic drag compared to a skin-tight jersey or skinsuit. Even having a jersey partially unzipped produces more drag than a fully zipped-up jersey. Don’t forget about the outer layers. While on your group ride, take off that flappy wind jacket just as soon as it starts to warms up.
Fourth, consider an aero helmet vs an oversized round one. Other things to consider, shaving your legs, skin-tight gloves, aero booties (shoe covers) all are things that will make you more aerodynamic.
The frame, or type of bike is next. A triathlon / time trial bicycle is the most aerodynamic. But if a road bike is your preference, then one of the newer aero road bikes would be worth considering. Most manufactures now have at least one high-end aero road bike that has been wind-tunnel tested.
In 2019, listed alphabetically and sorry if I missed any, there are 22 (and counting) great options including, but not limited to 3T Strada, Argon 18 Nitrogen, Bianchi Aria, Bianchi Oltre, BMC Timemachine Road, Boardman Air, Cannondale SystemSix, Canyon Aeroad, Cervelo S5, Colnago Concept, Giant Propel, Lapierre Aircode, Merida Reacto, Orbea Orca Aero, Pinarello Dogma, Ribble Aero, Ridley Noah Fast, Scott Foil, Specialized Venge, Storck Aerfast, Trek Madone, Wilier Centro.
Aero road bikes are narrower – forks, frames, seatpost, hidden (internal) cables – are all designed and built to slice through the wind more efficiently than a climbing bike.
Deep dish aero wheels will be your next consideration. Wheels make a big difference. Current trends for aero road bikes are borrowed from the triathlon setup of having a larger depth wheel on the rear and a shallower wheel on the front. You’ll find a lot of 40mm+ front wheels and 60mm+ rear wheels, although many manufacturers are also providing 60mm+ wheels for both front and back.
Tires impact not only aerodynamics but also rolling resistance. Although the most efficient tire is a tubular, there are many low rolling resistance tubeless and clincher tires available. Make sure to match up the tire width with the rim width for the best aerodynamics.
Aero bars vs Round bars. I’m not talking about triathlon style aero bars. I mean an aerodynamic road handlebar that is flattened along the top. If you want the best aerodynamics, leave off the tape as testing shows that even applying handlebar tape can cost you several watts of added wind drag.
Exposed cables vs fully internal cable routing. This is something that is designed into the frame by the manufacturers. Referring to the list of aero road bikes above, go back through the list and look again at all of the aero bicycles. Some have exposed cables routing under the handlebar tape and to the brakes and derailleurs while others bikes have full internally routed cables. Bikes with internally routed cables will have less aero drag than those with exposed cables. In my opinion, this is 2019, all aero road bikes should have full internally routed cables.
When Does All of This Aero Stuff Matter?
If you are riding at less than 15 mph (24 kph), then you won’t see much of a difference in terms of aerodynamic efficiency. In fact, referring to the table below, a 180 pound rider with a 0.5 mph headwind on a flat road is only using 42.4 watts of power to push through the wind.
If you ride at these speeds you really won’t need to upgrade to an aero bike, unless you want the latest in design technology. But, the faster you want to go, the more exponentially increasing resistance you will have to face.
Referring again to the table at the bottom of the page, you can easily see why going from 30 mph to 31 mph is so difficult. This tiny 1 mph increase requires 33.5 additional watts (328 watts to 361.5 watts), which is about the same total power required to ride along at 14 mph. Going from 37 mph to 38 mph requires 50.5 additional watts.
The motorcycle industry figured out long ago that aerodynamics matters. These 1000cc MotoGP monsters have an estimated 300HP and achieve speeds of 220mph on the race track. Think of the wind these things have to push out of the way.
As vehicles get even faster, they tend to get lower, narrower and longer (ex., NHRA Top Fule Dragster). That means that aerodynamics play an even larger role — part of which is just to keep the vehicle on the ground. At 300 mph, the front wing produces 700 pounds of downforce while the rear wind produces over 5,000 pounds of downforce. These types of vehicles require a major focus on aerodynamics and physics to get down the track. This stuff is fascinating to me, but for another article.
By going aero on a bicycle, the penalty is (a) slightly heavier bike and (b) a bike that is not quite as stiff in the bottom bracket (compared to a pure climbing bike).
But if you want to go faster, getting into a more aero position and using more aerodynamic bicycle componentry will get you much further than just having light weight bicycle.