Aerodynamics in cycling and how to be faster with no additional effort

There are a number of factors which determine how fast you can ride.  The biggest, of course, is your power output, followed by your position, your riding equipment (bearing friction and tire resistance for example), and your weight.  Additionally the road grade, wind speed/direction, temperature and even elevation all play factors in determining your velocity on a bicycle.

Becoming as aerodynamic as possible is by far and away the best way to improve your cycling velocity with the least amount of effort.  The below chart (Figure 1) illustrates how a velocity is affected by a cyclist's power output and body position on the bike.  Hopefully we all know that the relationship between power and speed is not linear (straight line).  Rather, it takes progressively greater amounts of energy (watts) for each mile per hour gained. 

Figure 1:  Relationship between Power, Body Position, and Velocity

  Figure 2:  The Effect of Hand/Arm Position on Power and Velocity

Figure 2 illustrates the effects of aerodynamics due to body position.  Two important points: (1) again the graph lines are not linear (as mentioned above); and (2) the bike speeds start close together at lower speeds and progressively separate.   With each additional watt, the more aero-position (aerobars) becomes increasingly faster than the less aero-position (hoods).  

Does Equipment and Weight Matter?

Having aerodynamic equipment is typically far more important than having light equipment.  For example:  two kilograms of weight savings for me would only drop my 40K TT by 3.6 seconds on a flat course.  Yet just adding an aerodynamic fork vs using a standard fork can mean a decreased time of about 30 seconds or even more for an over-sized round fork - up to 50 seconds.

Weight does play an important role for climbing, and accelerating and for rotating parts such as wheels, shoes, pedals and cranks.  In a nutshell, lighter is better.  But keep in mind that once your equipment is up to speed its weight becomes significantly incredibly less important (including wheels).  Once you have broken the 10 mile per hour speed (16 kph) barrier (no wind) aerodynamics is again king for determining ultimate velocity.  At speed below 10 mph (16kph) aerodynamics are generally not in play. See Figure 3 (below) for an illustration of road grade, speed, position and aerodynamics. 

Figure 3:  road grade, position and aerodynamics v. speed

The funny thing about cycling and hills is that you can not recapture the loss of speed from climbing by going down the same  hill.  Let me give specifics to illustrate this:  I can ride 10 miles (16.1 km) on a flat road, in my drops, at an average speed of 26.18 mph (42.1 kph) in 22.92 minutes at 340 watts.  With the exact same effort and position, I would travel up a 5 mile (8 km) hill with a 6% grade at an average speed of 12.59 mph (20.26 kph) in 23.84 minutes.  Going downhill, I would average 41.94 mph (67.5kph) and complete the descent in just 7.15 minutes.  The combined incline and decline results would give an average speed of 19.36 mph (31.15 kph) and a travel time of 30.99 minutes.  In short, this hilly course (the same total distance as the flat course) would slow my average speed down by 6.82 mph (10.97 kph) and add 8.07 minutes total travel time compared to a flat course.  Incidentally,  if  I didn't pedal at all on the down hill section I would only lose another  0.76 mph (1.2 kph) average speed and add 1.25 minutes to the total travel time.  There is not a good performance return for pedaling down steep hills. 

Do Tires Matter?

Figures 4 and 5 (below) provide additional support, and are followed by  real treat for readers who are techno geeks like myself.  The figure 4 shows that narrower tires have greater rolling resistance, but yet are still faster because of aerodynamics!  Figure 5 shows that tubular tires have less rolling resistance than clinchers.  (So tubulars are lighter, faster, and corner better.... yes they cost more).

Figure 4:  Effect of Tire Width on Rolling Resistance

Figure 5:  Effect of Tire Width on Power Output

 Bike Calculator

And now the real treat (or at least I think it's the bomb) is a bike performance calculator.  It is massively cool for allowing you to see the effects of wind, weight, power, temperature, elevation, body position, and even tires on cycling performance.  After inputting a few values, this handy calculator will determine your velocity, time, calories, and weight loss.  From my real world experiences, I have found it to be amazingly reliable, but I should point out that it is only a model and is not without some degree of flaw.  But judge for yourself.  

Figure 6 (below) is an photo image of the calculator , and if you click on the title you will be linked to the site that hosts it.  I have also added it to my sidebar as a link titled "Bike Calculator" under "Links to people and things that I like".  

Figure 6:  Bike Calculator

Drafting Aerodynamics

The effects of aerodynamics is HUGE in road racing, time trials, criteriums, and even sprinting.  For example, drafting can reduce oxygen costs by 25 to 40 percent.  Figure 7 (below) offers a great illustration of the effects of aerodynamics and drafting:  a world class track team time trial riders can produce the following average wattages in a pace-line (traveling around 35 mph):  

First rider will produce around 607 watts (+/- 45), 

2nd rider 430 watts (+/- 39), 

3rd rider 389 watts (+/-32), 

4th rider 389 watts (+/-33).  

Notice that there is a decreasing advantage drafting in 3rd position over 2nd, but no further advantage after 3rd position.  (From this and other points within this post you can deduce that your front wheel is more important than your rear wheel concerning aerodynamics and performance, yet the rear wheel still matters!)

Figure 7:  Drafting Aerodynamics Illustrated

Ideal drafting greatly reduces a riders energy expenditure (as discussed above) and is a critical component of bicycle racing.

In order to increase your velocity while sprinting, it is extremely valuable to have a good aerodynamic form.  This means producing the smallest frontal area possible, along with a streamlined position.  So put your head low, back flat, and ideally keep your elbows in (if power can still be generated sufficiently).  Mark Cavendish and all the sprinters pictured in the photo in this link have perfect aerodynamic form while sprinting.  

 

Conclusion:

To summarize, an aerodynamic wheel is more valuable than a lighter wheel for most racing applications.  Weight plays a larger role concerning velocity during acceleration and hill climbing (especially for rotating parts such as wheels, shoes, pedals and cranks).  On flat courses, after accelerating, the weight of a wheel (etc) is almost a non-factor when compared to the performance effects of a highly aerodynamic wheel. 

A rider would be wise to ride in an aerodynamic position at all times where the speed is above 10mph even when drafting in a field (riding in the drops vs sitting up with hands on the bars).  

Pedaling hard down descents is not very productive due to the increasing effects of wind resistance.  Average speed can be increased on a hilly courses by careful disbursement of increased effort on uphills and lessening to no effort on descents vs a constant effort over that same distance.

Consider the information provided here and ride accordingly.  Your senses can not perceive the energy savings or the speed increases from good cycling form, but all of the measures devices (speedometer, watt-meter, etc.) can and will.  It can make the difference between winning and losing.  

If I can think of any more useful points I will add them to this post over time.  Any suggestions are appreciated!   

To learn about the best video camera in the world for videoing cycling (which is the cameras that I use for my videos) click here.