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Osman Isvan
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Internal and External Factors

For the most part, the experience of riding a bicycle can be summed up as trying to go as fast as possible with the least amount of effort. Regardless of the relative priorities we assign to high speed (performance-oriented cycling) versus low effort (comfort-oriented cycling), the relationship between these two goals defines the sport of bicycling. Of all the factors that affect this relationship, hills and winds are by far the most influential. Certainly nutrition and training, body weight, bicycle weight, loads carried on the bike and on one’s body, riding position, tire inflation pressure and a few other factors are very important, too; but optimizing these variables, which are to some extent under the cyclist’s control, is an integral component of the sport. So, the only “external factors” are winds and hills. As an avid cyclist and amateur physicist, I have given quite a bit of thought to these factors, and have written technical papers to publish my findings over the course of several decades.

Spoke Divider

Spoke Divider

Wind and Speed

The first of these publications, titled The Effect of Winds on a Bicyclist’s Speed, appeared in the June, 1984 issue of Bike Tech, Bicycling Magazine’s Newsletter for the Technical Enthusiast. In that paper, I looked into how the ground speed of a bicycle would change in response to winds at different speeds and from different directions, with the same propulsion power. The findings published in that paper, about how time-trial results are affected by wind speed and wind angle relative to a straight-line out-and-back race course; and the effect that a given wind has on the average speed of a cyclist on a circular route, spurred some initial controversy and led to further investigations by more authors including Jobst Brandt, Douglas Milliken and others.

Human and Battery Power Constraints

The idea of modeling the cyclist as a source of constant power is rooted in the principles of biomechanics and exercise physiology. Electric vehicles, in total contrast, are constrained mainly by the amount of energy contained in a battery. This unique paradigm makes an e-bike (or pedelec) a particularly interesting hybrid vehicle, because power is available from two complementary sources: a primarily power-limited source (the rider) and a primarily energy-limited source (the battery). Specifically, under given wind and terrain conditions, the range that can be covered under electric assistance, and the shortest time possible to complete a given course, depend on when, where and how much human and electric power is applied. A strategy for managing the electric power according to wind and hill conditions is the subject of my second article on the topic, which is titled “Power Optimization for the Propulsion of Lightweight Vehicles”. That article shows, among other things, that contrary to common assumptions, proportional assistance is not the best strategy for managing the hybrid power.

Spoke Divider

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Advances in Instrumentation

Recent developments in bicycle instrumentation, combined with the standardization of digital wireless protocols with encoding technologies for data exchange over ultra-low-power radio transmissions, make it possible and practical to measure and record much more data about a bike ride. As a result, cycling computers are now able to display and analyze numerous parameters including GPS coordinates, cadence, heart rate, ambient temperature, barometric pressure and many others. Curiously, wind speed is absent from the list of available metrics, even though it is well known that wind conditions play a significant role in bicycling. Development of wind sensors for bicycles would make power meters accessible to more cyclists, and wind-aware cycling computers would spawn new concepts such as crowd-sourced wind maps and more. I present these ideas in the article The Relevance of Winds in Bicycling.

Spoke Divider

Spoke Divider

Power Analyzer

As a proof-of-concept prototype, I developed a power meter and data analyzer, called Power Analyzer, which currently runs on a spreadsheet program waiting to be turned into a smartphone app, or a firmware upgrade that can potentially turn an existing bicycle computer into a power meter. In the recent article Measuring Cycling Performance, I describe the operation of this prototype and compare its accuracy with two other power meters running simultaneously on the same bcicyle during actual rides.

Spoke Divider

Spoke Divider

Links

The Effect of Winds on a Bicyclist’s Speed

Power Optimization for the Propulsion of Lightweight Vehicles

The Relevance of Winds in Bicycling

Measuring Cycling Performance

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