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
Rider
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.
Bike
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.
Summary
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.
Nice article coach Rick. I can see the benefit of an aero frame and wheels but I’m a very light rider ( <130#s ) and worry about an aero setup's sensitivity to cross winds, especially when it's gusty. Should I be concerned?
Steve, So much of the bikes sensitivity to crosswinds is dependent upon the shape(s) of the frame and wheels. The geometry of the frame will impact your comfort so there are several things going on here. For example, if you come from a triathlon background, then an aero road frame that is closer to a tri bike would be more comfortable for you. In this case I would choose a Cervelo S5. If you come from crit or road racing then a Trek Madone might be you bike of choice. Again, these are just examples. The biggest sensitivity to crosswinds would be the size of the wheels. I would go with something like a 35mm or 40mm rim for both front and back. Hope this helps
Good points, especially about the wheels. I’ll keep that in mind for my next bike.
Thanks Coach!
Great article, but I think I think the reality of this is that there are multiple answers. The faster you ride, the more aero matters. That point is clearly made here. However, for climbs and punchy accelerations weight is more important. The harder and more frequent the accelerations/climbs, the more weight matters. Very similarly to the way aero is more important at greater speeds. Secondarily, as pointed out the rider is exponentially more important than the bike for both weight and aero. A human can lose 100 lbs; a bike can not. A riders clothes and position can cut an aero signature in 1/2 or more; internally routed cables or flat top bars can not. Fortunately, most modern bikes are built to be light and aero, so everyone with a newish bike has a pretty level field to start from. If you want to get faster on a bike: 1st ask am I over weight. It is far cheaper to pull 5 lbs off you body than your bike. 2nd get a good bike fit that can put you into a good/safe aero position on the bike for longer periods of time (and train to push power while maintaining that position). All your expensive aero gear is worthless if you’re sitting up with straight arms, and your hands on the tops of the bars. 3rd remember, aero gains from drafting are still far greater than any purchased gains a bike can offer, so if you want to race faster, consider working on race strategy. That is how I think you get fast on a bike. When you’ve done all that and you’re trying to improve your average speed on a flat windless day from 22 to 23 mph then you should start thinking about switching from a round bars to flat top bars.
PS. Cheapest way to save weight on a bike: racing tires, racing tubes, lightweight skewers, and a light weight saddle. Also look at what’s in your saddle bag. For pretty standard equipment, you can shave 2-3 lbs just by doing your homework here at a cost of around $200-300. As opposed to grabbing a new set of 200-400gram lighter carbon aero wheels for $1.5k-$2.5k.
Not sure that wattage table is correct? 100 watts to go 20 mph? Analyticcycling.com says it’s more like 170 watts. What am I missing?
https://analyticcycling.com/ForcesPower_Page.html
Refer to his graph at bottom of page… 500w to go 10 mph? 3,000w to go 25mph?
That doesnt sound right either.
Another problem with a analyticcycling.com article – https://analyticcycling.com/PedalOpCrankLength_Page.html
Their results directly conflict the Jim Martin crank length study – https://www.ncbi.nlm.nih.gov/pubmed/11417428
This study concluded that while the power was maximum with a crank length of 145 mm there was little lost by most riders when using 170 mm cranks because the difference was only about 1%. Let me repeat, Martin found that in his study POWER WAS MAXIMUM AT A CRANK LENGTH OF 145mm. It is strange to me that even though the difference in power between the 145 and 170 mm cranks did not reach statistical significance Martin would have concluded that crank length didn’t make any difference to the racer.
analyticcycling shows that as the crank length increased, so does power.
So do lite and aero for the best of both plus adjust your position to a more to cheat the wind.
” exponentially increasing resistance” when did everything that is not linear become exponential? I see this all over the place and even with my engineering students. Exponential function is faster than something raised to any single exponent; it does not mean than an exponent is involved. Power lost due to air resistance goes as the cube (3rd power) of speed, See the table: twice as fast is 8 (2 cubed) times the power.
There’s nothing wrong with analyticcyling’s chart. They are using meters per second for speed. Thus, 35 mph would require 978.8 watts, which corresponds well with my experience.
Does this chart represent numbers based on a flat course? What about a hilly Ironman course? For example, Ironman Lake Placid has 5 significant climbs with the lowest grade being 1.5% and the highest 3.4% for an average of 2.28%. The total amount of miles for the climbs on the course is 35.98 miles (this is considering both loops). For that amount of climbing on that course, what is the ideal combination? Would it be a lighter aero road bike with maybe 55mm rims to help with the climbs or an assumed heavier TT bike with deeper rims?
I’m very curious about this debate, aero vs. weight. What about a situation like a criterium race? When I view my ride data after an hour event, I see hundreds of micro power spikes. Rarely am I holding a steady pace, rather constantly accelerating and slowing down, and most of the time you are drafting while this is happening. I would really be interested to see if anyone has done any testing in a situation like this. I’ve done road racing and it’s a little different then a 6 turn criterium. I definitely see the advantage of riding Aero bike on a solo effort or with a small group at a steady pace. I would think that lighter bike with lighter low profile, say 40mm wheels would be more appropriate in a criterium race with all the micro accelerations going on. My thought is power to weight ratio, like on a race car, wouldn’t a lighter car, brake and accelerate quicker then a heavier car, especially if it is drafting in a group? I’m considering purchasing a new bike this year, and trying to decide on something like a Scott Foil or Canyon Aeroad, vs. a more conventional lighter bike. It’s funny that when I’m at the races, you see everything from box style rims to 62mm deep dish, aero frames and standard frames, and everyone has an opinion. I think if we all just ride/train a couple more hours a week, that would make more of an impact on our performance. LOL
Excellent article. I’m 55, 6′-0″, 150 lbs, and fairly flexible. Been riding 5 years, recently joined Strava and was surprised to learn that I’m a very good short segment climber with a few top 10’s on my local, 30 mile route, which has many small hills, on my Ridley Helium SLX (rim), with slammed (no spacers) 8 degree X 120mm stem, with mechanical Ultregra (so 4 cables exposed to wind) with CLX 50’s, but my solo avg, speed is only barely 18 mph on a good day. Thinking about getting my first aero bike and curious about wheelbase as a factor. Obviously, a longer wheelbase means more fame, more weight, and less agility, but a short wheelbase means your straight line movement is going to be a little more “squiggly” for lack of a better word, and therefore you’ll actually have covered more ground than with a longer wheelbase.
You’ve chopped a couple of positions off of that photo, as for Tri bones being the most aerodynamic, heard of battle mountain?
https://1.bp.blogspot.com/_5PAf404x7S8/Rk8TLUs0dzI/AAAAAAAAAxE/kc8Xp6eRvi4/w1200-h630-p-k-no-nu/lowraceryx7.jpg