Cycling Science: 7 Fascinating Facts About Bikes
By Max Glaskin, Popular Mechanics, 3 December 2012.
By Max Glaskin, Popular Mechanics, 3 December 2012.
The author of the new book Cycling Science reveals nuggets about the world's most popular form of transport. (Follow Max Glaskin's blog, and find him on Twitter.)
1. Easy Riding
Put a person on a bicycle and they become the most efficient creature on Earth. No other living thing can expend so little energy for so much self-powered travel. And that's just when riding along level ground. When a person rides downhill, the free energy from gravity reduces the demand on the human body even more.
If a cyclist and a pedestrian expend the same amount of energy, the efficiency of the bicycle means the cyclist will be traveling three times as fast. At an average walking pace, the walker uses more than six times the amount of metabolic energy above the resting level compared to the cyclist.
Running is four times as energy-greedy, and neither they nor other self-propelled athletes, even the world's fastest, can keep up with a top cyclist. Usain Bolt ran at 23.35 mph in the 2009 Berlin World Championships, but for less than 10 seconds. Speed skater Jeremy Wotherspoon set a world record of 32.87 mph over a 547-yard course. But no athlete could run or skate the 35.03 miles that Chris Boardman rode in one hour at the Manchester (U.K.) velodrome in 1996.
When it comes to muscle-powered traveling, nothing beats cycling.
2. Safety in Numbers
The more people cycle, the safer the roads seem to become. That's not just true for cyclists - it's true for all road users, even drivers confounded by the influx of bikes.
In Portland, Oregon [USA], all deaths from traffic accidents declined from 46 to 28 per year between 1997 and 2007, while the number of cycling trips quadrupled to total 6 percent of all journeys by 2007. Similarly, cycle use in the Netherlands increased by 45 percent from 1977 to 1997, while cyclists' deaths fell by almost 40 percent. In Berlin, between 1990 and 2007, the share of bicycle trips doubled to 10 percent while serious injuries to cyclists fell by 38 percent.
The phenomenon of safety in numbers is not so hard to understand. A growth in the number of cyclists makes them more visible, and drivers change their behaviour accordingly. Cities are more likely to provide safer road designs and facilities for cyclists when there are more of them about. And when some drivers switch to cycling, it means there are fewer cars on the road, which reduces the chances of anyone colliding with a high-speed chunk of metal.
3. Banishing Bumps
Suspension is meant to improve comfort, handling, and efficiency, but it incurs a cost: complexity, price, and weight. It may demand more effort out of the rider, since the spring system absorbs some of the rider's energy. That's why bike suspension systems, which were popular in the 1800s before the arrival of the pneumatic tire, vanished almost completely after good tires came around.
Now suspension is in fashion again, thanks to mountain biking. Engineers first designed front-wheel suspension (hardtail) then both front- and rear-suspension (full suspension) mountain bikes to take on ever rougher terrain.
The benefits and disadvantages of riding with a rigid frame, hardtail, and full suspension have been analyzed in scientific experiments. One lab has shown that, when riding over a 2 1/2-inch bump, front suspension reduces the vertical forces by 37 percent and lessens the horizontal forces by 28 percent. Those horizontal forces slow you down, so if you can reduce them by over one-quarter, it takes significantly less energy to propel the bike forward.
4. Balancing Act
Astonishingly, a bicycle can stay upright without a rider as long as it's moving at about 8 mph or faster. You just need a few ingredients.
First, a bicycle needs a freely steerable front wheel. Second, the more relaxed the angle of the fork, the more stable the bike. Third, the distribution of the handlebar and fork mass has an additional effect on how the steering reacts to a change in verticality (wobble). For example, a bike with a handlebar basket full of bricks will be less stable than one whose low-rider front panniers carry the same heavy load.
Put these three properties together in the right proportion and the result will be self-stabilizing dynamics. One explanation for this weird phenomenon is that when the moving bike begins to lean to one side, gravitational torque rotates the front wheel away from straight ahead and the bicycle starts to describe a circle. In reaction, the road surface applies a centripetal force that restores the wheel to pointing straight forward. The centripetal force also exerts a torque on the entire bicycle, which pushes it out of the leaning stance.
5. Material Gains
In 1817, Karl Drais invented the hobby horse (or dandy-horse) in Mannheim, Germany. To build this technological breakthrough and bicycle precursor, he used wood from the ash tree (Fraxinus), which was popular among coachbuilders because its grain is straight, it's easily shaped and joined, and it has good overall strength relative to its weight.
Since then, frame design has been propelled by advances in materials and technology. With the right combination, the optimum bike frames are now sufficiently strong, light, durable, and stiff enough to race down alpine roads at 50 mph, cross fields of boulders, or land in one piece after a triple back flip.
Frame builders have fashioned metals, polymers and man-made composites to allow riders to travel farther, faster, for longer. Improved manufacturing methods include extruding tubes from blocks of hot metal, varying the internal diameter of tubes to cut weight yet retain strength, and hydroforming aluminium into computer-designed profiles. Jointing and assembling now uses TIG welding for titanium and totally automating fabrication with composites.
The first hobby horse weighed about 45 pounds. Today's frames are so light that the Union Cycliste Internationale (UCI), the sport's governing body, prohibits racing bikes under 15 pounds.
6. The Invisible Foe
Every cyclist knows the burn they feel from defying gravity to pedal uphill. But the ubiquitous factor fighting cyclists' performance is air. Dry air at sea-level pressure (about 14.7 psi) and at 70 F, has a density of about 0.075 lb/ft3. Good aerodynamics reduce how much a cyclist is impeded, but only so much.
That hasn't stopped some cyclists and scientists from trying to defeat drag. The velodrome at the 2012 London Olympics was engineered to raise track temperatures to 82 F and make the air thinner, boosting the likelihood of world record times. Outdoors, however, the only strategy to defeat air is to go race at higher elevations where it's less dense. That's one reason Jennie Longo chose Mexico City for her world hour record bids in 1989 and 1996. At 7342 feet above sea level, the density of dry air at 60 F falls to below 0.062 lb/ft3, which gave Longo an extra 0.93 mph compared to recent rides she'd made at sea level.
7. Brain and Brawn
Winning cyclists must believe in themselves - but be wary of trusting their own brains. Research shows that the brain lies to the body and prevents it from fulfilling its potential. The brain sends us alerts to slow down or stop in the form of fatigue and pain because it thinks the body might be damaged if you exercise past certain limits. Top cyclists, however, know through practice that they can ignore the warnings and ride through the "pain barrier" to finish faster (although utterly depleted).
This means the right psychological preparation for competition can be as important as physical conditioning. Consider one study of cyclists on a hot ride; those who were lied to and told the temperature wasn't really as bad as it was rode faster than those cyclists who hear the true figures.
Choosing exactly the right training music for each rider is a growing field for experts. There is a host of research into how athletes can associate emotional states with optimal training so that similarly good performances can be triggered through emotions during competition.
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