MooGal- 650 vs 700

Thought this might be of interest-

Nanci

“Tri” Physics: Challenging the ‘Old Wives Tales’ with Science April 1, 2004

“Tri” Physics. Of course, all pun intended. This is the first in a regular series where we will discuss, debunk and otherwise attempt to understand, how physics affects us as multisport athletes. Most importantly, we will try to deal with topics that give speed for “free.” That is, improvement without the hard work of training or where training is enhanced. We’ll follow a loose thread as we weave are way through the various questions and “old wives tales” which permeate the sport. We will try to stay away from “religious positions.” It is not the intent to slam any ones training beliefs or equipment. Many different things work for different people. Just because something doesn’t conform to the best practice doesn’t mean it won’t work for you. Best case in point is Eddie Merckx, the greatest cyclist ever. He was a decidedly heal down peddler. Not an optimum position, except in a hard climb. The worst thing that anyone could have done would have been to try to change this natural style. However, in the general context, we will look at questions that will make you faster, stronger, and better for the run, if you “Tri” the physics.

A couple of things about me. I have a Ph.D. in applied physics and my specialization is time-series analysis; that is, data analysis. I was in the first group of physicists to hit the financial industry in the mid-80’s. Over the course of a career, I have held positions from trainee to CEO, and worked on financial modeling, hedge fund and derivative trading, intelligent decision systems, hurricane and tornado wind fields, catastrophe theory, and large-scale system and computer network modeling. For the last 2 years, my passion for sport has completely taken leave of my senses. Thus, you find me in my current position as CEO of John Howard Performance Sports. Over the last 22 years, John Howard Sports has trained athletes to over 130 National Titles, 12 World Titles and an Olympic Gold Medal.

So what are examples of these “old wives tales” that we talk up a storm and argue about constantly? Do ‘bigger people’ go downhill faster? Really? Are ‘tri’ bike configurations indeed better than road bike configurations for triathlons? Why? What’s the difference anyway? Are taller swimmers faster in water? These ‘tales’ will be challenged and explained over the next few months. We will also have an article discussing the various ‘techno babble’ of our sport. Things like ‘rolling resistance’, mass vs. weight, and speed vs. acceleration, spin vs. hammer, etc.

We thought this article should be more than an introduction of what’s to come. So let’s attack one of the more common arguments: Wheel diameter. In other words, do we choose 700 or 650 wheels? The rational for 650 wheels came from experimentation in the European Peleton. Various wheel size and funny bike configurations were attempted to reduce drag, rolling resistance and enhance acceleration. The current “Tri” setup of 650 wheels front and rear vs. 700, specifically came from an idea that 650 wheels would accelerate faster, have less weight and lower rotational resistance. The first couple of points are true in that 650 wheels accelerate faster and can be lighter. Whether or not the rolling resistance is better is dependent more on other factors than just the size.

So are they better, is acceleration and weight a reason to use 650 over 700 wheels. It is true that in a super short Prologue Time Trial where a fraction of a second makes a difference; there might be some justification. Prologues are less than 7K, typically being 3-6K, where a second can separate the podium places.
So are they a better choice for multisport distances? The answer lies in gear inches. The 700 wheel for the same power/cadence covers more ground, pure and simple. The bike goes farther for each pedal revolution with 700 wheels. A rider with 650s will always have to spin a faster cadence, or apply more power to make up for the gear inch deficit. So no advantage and actually a real disadvantage with 650 wheels. This goes hand in hand with spinning a small gear vs. mashing a large one. It is always, faster for the same effort to mash a big gear vs. spin a smaller one. Again it's pure gear inches. If one cannot get on top of a big gear that's a different story. For the same effort though, the big gear wins all the time.

More explanation is necessary here in terms of aerobic endurance vs. muscle strength vs. muscle endurance. If one has muscle strength as a limiter, but has strong aerobic endurance, then spinning can be a performance advantage over mashing. The pure physics point is a simple one and is back to the idea of gear inches. So where does the advantage come in, from spinning vs. mashing. Certainly, never in a flat sprint and always in a hard climb. Setting this simplistic example aside, for triathletes, the answer is more complex and lies with a different question: What is the relationship between power, weight and aerodynamics? More to the point, how does one optimize among these parameters. Right off let’s throw out the climbing side. Weight counts when the road turns up. The more up, the more weight counts. For a non-climbing event, there is a rule that can be applied: Aerodynamics trump weight, power trumps aerodynamics.

The above rule holds true for all, except low power riders. Riders putting out less than 200 watts average over a sprint distance (40K), need to be mindful of weight at some expense to aerodynamics, as these riders do not have enough power to accelerate the weight. They loose the advantage of the aerodynamics to not being able to keep the effort up. For all others, do not compromise aerodynamics for weight. The aero advantages will always be greater. By the same token, never compromise power output for a more aero position. Power to the pedals is the goal. It doesn’t matter how aero one is if the position does not allow for maximum power output.

We’ll look at these and other questions, in more depth, in future columns. Let me know your questions. This column will be most effective targeted at issues, which drive your everyday quest for a faster bike segment, a better transition to the run, and more power and endurance through it all.

Richard T. Gordon, Ph.D.
CEO
John Howard Performance Sports
http://www.johnhowardsports.com