Tag: Science

Is a Lighter Bike Faster?

I enjoyed this article in VeloNews, it explains why I like my Atlantis so much

If you’re having trouble telling what the difference is between the 11 pound bike and 15 pound bike, save yourself the eyestrain. That’s the message.Take 3 pounds off your bike, pedal at a constant rate of 200 watts, and you’ll get to the top of a 7 percent climb a whole 7.5 seconds ahead of the competition. A 1-pound advantage only puts you ahead by 2.5 seconds.

Editor’s Note: This excerpt is adapted from the book FASTER: Demystifying the Science of Triathlon Speed by Jim Gourley and republished with permission from VeloPress. Learn more about the science of triathlon at freetrispeed.com.

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.

But more insidious than inaccurate vocabulary is a simple overestimation of how much bike weight matters for most riding.

In FASTER, I show the math that explains why just a degree or two of incline makes riding a bike feel so much harder. Riding up a hill, it may seem more important than ever to dump any and all extra mass we can from our bikes. That’s the allure of a carbon fiber bottle cage, an upgrade to carbon fiber cranks, handlebars, stem, carbon saddle rails, or wheel spokes. Five grams here, 10 grams there, it all adds up, right? Pretty soon, you’re 500 grams lighter. That’s half a kilogram!

True. But such upgrades could easily total $500 or more, which is also half a grand. Is it worth it?

Not exactly.

A good approximate difference between an entry-level aluminum bike with a decent set of components and a top-of-the-line carbon model with some of the lightest components on the market is just shy of 3.25 pounds.

Was the weight loss worth it?

Let’s find out. Take a hypothetical rider and have her ride two bikes up a hill at the same speed. The first bike weighs 15 pounds and the second bike will shave off the 3.21 pounds to weigh in at 11.79 pounds. For each test, we’ll have her ride at 15 mph. Everything is constant, except for the bike, so what we ought to see is a reduction in the power required to get up the hill. That’s the real test of your savings.

Refer to the second image, above, for a graph of the results.

If you’re having trouble telling what the difference is, save yourself the eyestrain, because there isn’t much — that’s the message.

But pro athletes use the lightest equipment they can, so there must be something to it, right?

Remember that professional athletes operate in an entirely different environment than the rest of us. They are all very close to each other in terms of fitness, and they are also all very close to being the absolute best a human being can be.

Beyond that, our result also makes intuitive sense: 3.21 pounds is just over 2 percent of the total weight of our 150-pound cyclist and 15-pound bike. Ten watts is 2 percent of the 500-watt power requirement to maintain speed up a 10 percent grade. Because the weight-to-power savings ratio is linear, we should expect that one-to-one relationship.

The implication is a bitter pill, though. If you want to reduce the power requirement by 1 percent, you have to reduce the total mass that’s moving up the hill by 1 percent. And because you’re moving both your body and the bike up the hill, a measly 1 percent equates to a whole lot of grams before you see returns on your carbon investment.

In short, you’re much better off upgrading your legs and dropping body fat through proper training and diet. In fact, losing unnecessary weight would have a dual impact on your power and speed. As weight decreases, the amount of power required to maintain a certain speed will also decrease. At the same time, the amount of power you are capable of generating should actually increase. This is because oxygen uptake is related to body mass and improves as fat is lost.

Wattage vs. time

If the power argument doesn’t quite satisfy you, we can look at it another way. Let’s answer the question you really care about: How much faster does it make me? After all, you win races by saving time, not watts. Let’s see what will happen when our hypothetical rider rides bikes of varying weight up different hills. We’ll hold power at a constant 200 watts and have her ride up a 1-mile climb at seven different grades (1–7 percent).

Let’s look at the difference between 15-, 16-, 17-, and 18-pound bikes, with the 18-pound bike serving as the baseline. Because of the complexity involved, we’ll eliminate air resistance and analyze the impact of weight reduction only. How much time do we save?

A graph of the results is in the third image above.

Read it and weep, weight watchers.

Look at the far right of the graph. Take 3 pounds off your bike, pedal at a constant rate of 200 watts, and you’ll get to the top of a 7 percent climb a whole 7.5 seconds ahead of the competition. A 1-pound advantage only puts you ahead by 2.5 seconds. Over the course of an hours-long race, a few seconds per climb is not a significant advantage.

Keep in mind that the advantage only holds when the climbs are long and steep. Courses with fewer and shorter ascents will keep the difference small.

Read more at http://velonews.competitor.com/2014/08/news/bike-weight-myth-fast-bikes_339880#b18u91L353YFsStr.99

Effective Cycling

"In cycling, practical experience still outruns science."

ForesterBradley Wiggins’ amazing Tour de France and Olympic gold medal wins has inspired us to take a break from swimming posts to dive back into John Forester’s Effective Cycling. Here’s an excerpt from Forester’s “The Physiology and Technique of Hard Riding” chapter:

Abilities of Cyclists

Cycling is by far the most energetic activity you can undertake. Other activities may produce more force, as does weight lifting, or more muscle power over a short period, as do track sprinting or most swimming events, but there is nothing that approaches the long-term, high-power demands of cycling. In these events, the cyclist is working as hard as possible in the most efficient way for many hours at a stretch—for 4 hours for a 100-mile race, for 12 or 24 hours for long-distance events, and even for several days in the longest events, interrupted only by the amount of sleep that the cyclist chooses. Stage races may require only 6 hours a day, but the biggest has 22 racing days in a month.

The contrast with many other activities becomes more apparent when cycles of motion are considered. Many weight trainers consider 20 or 30 repetitions adequate. A long swimming race may require 500 strokes. A marathon run requires about 30,000 paces. The 200-mile ride, which is probably cycling’s equivalent to the marathon, requires 50,000 pedal revolutions. Even the century ride, which cyclists of all types complete, requires 25,000 revolutions. The world’s record of 507 miles in a day probably required more than 100,000 revolutions.

These demands for energy, and the ability of first-class cyclists to meet them, exceed the boundaries of our physiological knowledge—at least as it is published in scientific journals. We do not have sufficiently accurate explanations of exercise physiology to enable us to recommend training practices for hard riding that are based on laboratory knowledge. Rather, we are still at the stage where the known capabilities, techniques, and experiences of hard riders are the base data for extending our present physiological theories of short-term exercise into the realm of long-term, high-power exercise. As a result of this inadequate knowledge, when current exercise physiology has been applied to engineering design for cyclists, such as in the design of bikeways, the results have been contrary to experience. One ludicrous result is the published criterion for bikeway grades, which states that the highest hill that most cyclists can climb is 34 feet high. Cyclists should be skeptical of all recommendations that have been made by exercise physiologists, for these are generally based on scientific theories that do not apply to the conditions of cycling. Scientists typically continue to apply generally accepted theories to particular situations, even when the data for one situation (cycling, in this case) refute the theory. In cycling, practical experience still outruns science.

Known Facts about High-Performance Cycling

Cyclists are able to exceed 25 mph on the road for up to 8 hours, and to exceed 20 mph for up to 24 hours. Competitors in these events, like sporting cyclists in general, ride with cadences between 90 and 110 rpm. Cyclists eat and drink while cycling. Cyclists who take early leads in massed-start events (as opposed to unpaced time-trial events) rarely are in position to contend in the final sprint. These are the known facts that must be explained by any legitimate theory of cycling.