By Will Murray and research from CU Boulder
In triathlon and other endurance sports, there are some things we know for sure that really, really work. Ingestion of caffeine to enhance athletic performance, administered correctly, really works. Selecting the right bicycle tire to go faster really works. For both of these things, enough unassailable research exists to say that we know these things for sure. Another thing we know for sure—getting into a more aerodynamic position in your bicycle reduces drag and lets you go faster.
Caffeine enjoys much research that heralds its ability to enhance endurance performance by as much as 9% in trained athletes. It works best if the athlete refrains from ingesting caffeine for perhaps two or three weeks before the big event. Here are a couple of explanatory pieces about caffeine. http://www.examiner.com/article/does-caffeine-improve-endurance-sports-p... and http://www.examiner.com/article/how-caffeine-affects-your-mind-during-ra...
Fast tires can have sufficiently less rolling resistance to make them up to 26.4 watts ,more efficient per set of two tires than slower tires. For an athlete whose lactic threshold is 200 watts, 26.4 watts is 13.2%, which means a lot in a race. Read more about selecting fast tires here: http://www.examiner.com/article/triathletes-find-free-speed-from-bike-tires
Now we get to wind resistance.
An often-repeated statistic tells most of the story: at 20 miles per hour on flat ground, 90% of the cyclist’s energy goes into overcoming wind resistance. The other 10% is in rolling resistance of the tires, friction in the drive train of the bike and such.
That said, anything you, the cyclist, can do to reduce wind resistance will let you go faster. Looking at modern bicycles gives you a hint that bicycle designers are on to this. Road bikes and especially time-trial bikes look more and more like airplanes, with fusiform tubing, airfoil handlebars and seat posts and even bladed wheel spokes. (When I showed my front wheel to my nephew, who designs turbine blades for a living, he felt the bladed spokes and muttered, “Wow! Nice coefficient!”). Aerodynamic helmets try to fill the gap behind your head, reducing turbulence and promoting laminar air flow over your back. Aero features on bikes and accessories are common.
Your gear can be as aero as it wants, but the most un-aero thing on a bike is the rider-that’s you. And sometimes slight differences in your body position can make a big difference in your aerodynamic-ness.
In their paper Measuring Changes in Aerodynamic/Rolling Resistances by Cycle-Mounted Power Meters,
published in 2011 in the journal Medicine & Science in Sports & Exercise, Allen Lim of Skratch Labs, Todd Carver, who founded Retul bike fitting systems, et al,, set out to measure just how much body position matters. Using commercially available power meters and a flat stretch of road in Boulder, CO, these scientists from the Applied Exercise Science Laboratory in the Department of Integrative Physiology at the University of Colorado tested real athletes on real bikes on real roads.
They tried four different tests: Using Powertap and SRM power meters on a flat, smooth asphalt surface in calm air, seven male and five female cyclists rode back and forth on a 200-meter test track. The cyclists rode on the hoods and on the drops to test aerodynamic differences, and rode with tires pumped to 60 psi and 120 psi to detect differences in rolling resistance. For rolling resistance, yes indeedy, they found a big difference in riding on hard versus soft tires, as much as 1 minute 30 seconds in a 40k time trial. That result will likely not shock you.
For aerodynamics, they also found a very large difference between riding on the hoods and riding in the drops. From their paper:
From the hoods to the drops position, our subjects decreased their drag area from a mean T SD of 0.36 T 0.05 to 0.32 T 0.05 m2, which represents an average decline of 10.8% T 3.5%. The minimum decrease from hoods to drops was 5.7%, whereas the maximum decrease observed was 17.8%.
By riding in the drops, a cyclist may reduce wind resistance at speed by an average of 10.8%. That’s a lot of drag to reduce. Again, from their paper:
Practically speaking, the relative decline from the hoods to the drops results in a proportional decrease in the power required to overcome aerodynamic resistance. For our subjects, this results in an average decrease from 290 to 260 W at 40 kmIhj1 at sea level when moving from the hoods to the drops. Assuming the same metabolic power output, that would translate to an average time saving of 2 min 6 s in a 40-km flat time trial.
For triathletes training and racing on a time trial bike, the bike puts you in a pretty aerodynamic position by design. As Eric Homestead, one of the authors, says, “Although you may be in your aero bars, that doesn’t mean you are most aerodynamic. Not all aero positions are the same. As you change the width of your aero bar position and the incline/decline, this will change your body profile (and thus drag and thus power and thus speed).”
Athletes riding a road bike can reduce drag greatly by learning to ride in the drops. Riding in the drops takes practice. At every opportunity, ride in the drops. After a while it will become normal. From casual, non-scientific, not-statistically significant observations from riding around Boulder and elsewhere, it seems that not that many cyclists ride in the drops. Next time you are out and about, do your own observation. But all this is at speeds of 20 mph or more, as wind resistance increases logarithmically with speed. At speeds below perhaps 15 mph, wind resistance is less of a factor. So when climbing, for example, sitting up to gain as much power from your pedal stroke makes sense, as there is little penalty for being un-aero at slow speeds.
When pushing into stiff winds, though, cyclists would do well to resist the urge to sit up and stay as aero as possible.
Eric Homestead is excited about the research protocol the authors developed. "The practicality behind this research is one of the great results. Testing your aerodynamic profile is now more accessible to cyclists and triathletes. You don't have to travel to a wind tunnel or simply guess anymore. If you have access to a power meter and follow the guidelines in the article, you can do this yourself."
Slicing you and your bike through the air when you are riding fast takes the most amount of energy. Whatever you can do to reduce wind resistance by making your own self more aerodynamic will result in and faster speeds on the bike. As you your own self is the least aerodynamic thing on your bike, whenever you can, get into the drops to make your body as aerodynamic as you can. The research says so.