 |
| Bicycle |
How much does your bike weigh? Chances are you’ve got a pretty good idea. You may have even bought it on the strength of how light it is, and have spent a good deal of money bringing this figure down even further. Good. How about your coefficient-of-drag area (cdA)? Good chance you can't answer that.
Let’s clear something up. There is no such thing as a “fast bike.” Bikes are neither fast nor slow. Bikes are shiny or expensive. Bikes have a lot of mass or a little. Without a rider, they are stationary. Physics holds a bike in place until you get on it and start pedaling. Even then the bike may not necessarily be fast. Of all the equipment on your bike, your legs are the most critical component. There are plenty of nice bikes on the road that are being ridden slowly.
Jim Gourley, a triathlete with an aerospace engineering degree from the U.S. Air Force Academy, tackles this topic in his book Faster: Demystifying the Science of Triathlon Speed. He did the math to see just how much speed a cyclist can save with a lighter bike. For starters, he estimates that switching from an entry-level road or hybrid bike with an aluminum frame to a top-of-the-line carbon racing bike with the lightest components on the market can save you about three pounds. Then he calculates how long it will take a cyclist riding four different bikes—15-, 16-, 17-, and 18-pounds—to get up a mile-long hill.
Even at the steepest grade he tested (7 percent), a one-pound difference between bikes only saves about 2.5 seconds—and the lightest bike only reaches the top 7.5 seconds faster than the heaviest one. "Over the course of an hours-long race, a few seconds per climb is not a significant advantage," he writes, at least not to an amateur cyclist or age-group triathlete.
One reason bike weight doesn't matter much is because it's only part of the total weight you're carrying, says Jim Martin, PhD, associate professor of exercise and sport science at the University of Utah. "It's easy to look at a 20-pound bike and a 15-pound bike and say, 'Wow, I'm saving 25 percent!'" he says. "But it's really just five pounds off your bike weight plus your own body weight plus your clothing, your water bottles, your gel, everything you've got on the bike. So it ends up being a much smaller percentage than it seems."
The Effects of Body Weight
A much more efficient—and economical—way to lighten your load is to shed body weight, says Gourley, not bike weight. Not only will it reduce your overall weight by a larger percentage, but it will also increase your VO2 max, which can automatically give you more power.
The heavier a rider is, the greater his energy requirements will be. This translates into putting in extra effort, especially during a climb. On rolling terrain and steep climbs, a lighter rider will come out ahead. The heavier rider will have less of an advantage because he will also have to overcome more gravitational forces.
Bicycling Magazine published the results of a study from James C. Martin, Ph.D., assistant professor in the department of exercise and sport science at the University of Utah. Using the calculations from a 160-lb. rider on a 5 kilometer, 7 percent grade, he concluded that for every 5 lbs. added to a rider, it would take him an additional 30 seconds to ascend a steep climb.
The heavier a rider is, the greater his energy requirements will be. This translates into putting in extra effort, especially during a climb. On rolling terrain and steep climbs, a lighter rider will come out ahead. The heavier rider will have less of an advantage because he will also have to overcome more gravitational forces.
Bicycling Magazine published the results of a study from James C. Martin, Ph.D., assistant professor in the department of exercise and sport science at the University of Utah. Using the calculations from a 160-lb. rider on a 5 kilometer, 7 percent grade, he concluded that for every 5 lbs. added to a rider, it would take him an additional 30 seconds to ascend a steep climb.
If you really want to upgrade your current ride without spending a lot of cash, there is one thing you should focus on: aerodynamics. "There's a saying in the cycling community that aero trumps weight, and I agree completely with that," says Martin. "If you can reduce your frontal area by 10 percent, you'll also reduce drag by that much," he says.
This holds true no matter what speed you ride, he adds. "There's this pervasive notion that aerodynamics doesn't matter if you ride below a certain speed, like 18 or 20 miles an hour. But the irony is that it can matter even more to slower riders, because they're out on the course that much longer." Reducing drag by 10 percent on a 90-minute 40K ride can save nine minutes, he explains; for someone who does it in 50 minutes, it only saves five.
This holds true no matter what speed you ride, he adds. "There's this pervasive notion that aerodynamics doesn't matter if you ride below a certain speed, like 18 or 20 miles an hour. But the irony is that it can matter even more to slower riders, because they're out on the course that much longer." Reducing drag by 10 percent on a 90-minute 40K ride can save nine minutes, he explains; for someone who does it in 50 minutes, it only saves five.
Conclusion
Q: So, did lighter bikes make you faster?
A: Not as much as you think
Shave your body weight first
before
shave your bike weight
(and your saving money)
Source:
https://www.outsideonline.com
http://www.velonews.comhttp://www.livestrong.com
cyling weekly magazine April 2017
Ride On!
