There are a number of factors that determine how fast you can ride. The biggest of course is your power output, followed by your position, the equipment that you ride (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 aerodynamic is by far and away the best way to improve your cycling velocity with the least amount of effort. Below is a chart that illustrates the relationship between power and body position on the bike and how a cyclist's speed is effected. We basically all know this and hopefully everyone knows that the relationship between power and speed is not linear (straight line). In short it takes progressively greater amounts of energy (watts) for each mile per hour gained.
Becoming aerodynamic is by far and away the best way to improve your cycling velocity with the least amount of effort. Below is a chart that illustrates the relationship between power and body position on the bike and how a cyclist's speed is effected. We basically all know this and hopefully everyone knows that the relationship between power and speed is not linear (straight line). In short it takes progressively greater amounts of energy (watts) for each mile per hour gained.
Above is another illustration of the effects of aerodynamics through 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. The aero-position becomes progressively faster than the less aero-position with each additional watt.
Aerodynamic equipment is far more important than light equipment. Two Kilograms of weight savings for me would only drop my 40K TT by 3.6 seconds on a flat course. Yet just an aerodynamic fork vs a standard fork can mean about 30 seconds and even more for an over-sized round fork (up to 50 seconds).
Weight does play important roles for climbing, and accelerating and for rotating parts such as wheels, shoes, pedals and cranks. To be quick about it, lighter is better. But keep in mind that once your equipment is up to speed it's weight becomes significantly incredibly less important (including wheels). Aerodynamics is again king for determining ultimate velocity when over the 10 mile per hour speed barrier (no wind). Below 10mph aerodynamics are generally not in play. See the below graph for an illustration of road grade, speed, position and aerodynamics.
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 what I am saying. I can ride 10 miles on a flat road at 26.2mph average in 22.91 minutes at 340 watts. If I travel up a 5 mile hill at 6% grade I can do it at 12.69mph average and 23.64minutes and then back down at 41.78mph average in just 7.18 minutes, for a total average of 19.46mph average and 30.82 minutes. In short, this hilly course slowed me down by 9.74mph and 7.91 minutes. Incidentally, if I didn't pedal down hill I would only lose about 6.5mph or 1.5 minutes (for the downhill section only). There's not a good performance return for pedaling down hills.
I have two more supporting charts and then I have a real treat for readers who are techno geeks like myself. The first is a chart that shows that narrower tires have greater rolling resistance, but yet are still faster because of aerodynamics!
My second and final chart shows that tubular tires have less rolling resistance than clinchers. (So tubulars are lighter, faster, and corner better.... yes they cost more).
And now the real treat (or at least I think it's the bomb) is a bike performance calculator. This handy calculator will determine your velocity, time, Calories, and weight loss after you plug in a few numbers. 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. It's amazing, but I should point out that it is only a model and is not without some degree of flaw. Judge for yourself.
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".
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| Bike Calculator |
Recap and a few additional points:
The effects of aerodynamics is HUGE in road racing, time trials, criteriums, and even sprinting. Drafting can reduce oxygen costs by 25 to 40 percent. Here's 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. First rider will produce around 607 watts, 2nd rider 430 watts, 3rd rider 389 watts, and 4th rider 389 watts. 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!)
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. Good form while sprinting would include producing the smallest frontal area possible along with a streamlined position. So head low, back flat, and ideally elbows in (if power can still be generated sufficiently). Mark Cavendish and all the sprinters pictured have excellent aerodynamic form while sprinting.
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!
I ride bullhorns in a very stretched out position when my hands are on the ends. I'm wondering how that would compare to hoods or aerobars, since they're sort of close to each. Typically, I end up so low that my forearms are on the bars, with my hands out as far as possible.
ReplyDeleteAaron, I would say in-between. Bull horns are a bit uncommon and not listed on the bike velocity calculator.
ReplyDeleteYour question reminds me of the '89 Tour De France where Fignon used bullhorns and Lemond used aerobars in the final and deciding time-trial
Had Fignon read this post before July 23, 1989 (and was reasonable) he would have easily won the Tour de France that year by over a minute, instead of Greg Lemond winning by 8 seconds
David,
ReplyDeleteDoes cycling jersey and expensive helmets make a difference in aerodynamics, or are they purely for comfort reasons?
Yes, they make a difference, but with qualifications. If we compare an inexpensive jersey with an expensive one then no on the performance (aerodynamics), but yes on comfort and function (zippers, fit, pockets etc).
ReplyDeleteIf we compare helmets, then more expensive typically does improve both comfort and performance (lighter, better vented, aerodynamic, etc), but generally the performance differences are small.
Aerodynamic performance really comes into play with Specialized time-trial helmets (long tail)and skinsuits. Both are fairly expensive (compared to standard helmets and jerseys), plus aero helmets aren't typically very comfortable.
Curious on your thoughts of going with a aero bike like a Scott Foil vs a typical roadbike. The data above suggest I would spend less energy with a road aero bike than I would with a standard roadbike even with a 1lb weight difference. I plan on buying a new bike soon for this season, I typically do road/crit racing. Thoughts?
ReplyDeleteJRodgers, yes I believe that an aeroframed bicycle has a slight advantage over the larger tubed lighter frames (the exception being long hills).
ReplyDeleteA couple points: water bottles can be an issue (mounting). They can be put behind the saddle, but this is not UCI legal. In the jersey pocket works though.
I'm pro aero frames and I think that bicycle manufacturers will start to trend (as an option) this way in the future.
In terms of performance in racing, first focus on good drafting skills and body position on the bike. This will produce the greatest benefit (by far!), then equipment starting at wheels, helmet, and then frame.
It all adds up!