The
Power Components Calculator
and
Power-Speed Scenarios Calculator
allow you to run calculations relevant to a simple course with one known distance, one heading, one wind bearing, and one constant gradient.
They may be ideal to model a simple cycling environment such as a velodrome or a single sector of a course that is of particular interest such as a climb,
but they do not realistically model a more complex course.
This model allows you to construct a course with up to 10 distinct sectors and this allows more realistic consideration of relative wind bearings and
gradients as well as variable effort. A number of pre-created courses are available on a public basis but if you are a registered user of this site you
may create your own multi-sector courses and reuse them in this model. Each sector can be specified in terms of power, speed, or allocated time and a single
course can include sectors specified in different ways.
Air Pressure Analysis
This feature may be of interest to Time Triallists who want to know how “fast” a particular day was. Based on your choice of atmospheric
air pressure and altitude this model will illustrate the “fastness” of these parameters relative to typical altitude-normalised atmospheric pressure data
collected over a 5 year period (2005-2009) in London, UK. For example, an air pressure of 1013 at the same altitude as the reference data would be reported
as “43rd percentile - 157 faster days in the year, 208 slower days in the year". Comparative advantage scenarios representing 0th, 25th, 50th, 75th and 100th
percentile air pressure also illustrate:
- Power differential required to match “today’s” time.
- Time & speed differential given ”today’s” power.
Inputs: Environmental Variables
- Temprature (Deg C). Input a temperature in degrees Celcius (e.g. 20)
- Pressure (Millibars). Input the ambient air pressure in Millibars (e.g. 1013). You can get this number from any good weather forecast.
- Relative Humidity (%). Input the ambient air humidity in percent (e.g. 20). Again you can get this number from a weather forecast.
- Wind Direction. Select the applicable wind direction as a heading (e.g. NW) or else input a wind bearing between 0 and 255 degrees. This is the direction the wind is blowing from, not to.
- Wind Speed (KPH). Input the wind speed in Kilometes per hour (e.g. 5).
Inputs: The Rider & Bike
- Rider + Bike Weight (Kilos). Input total weight in kilos (e.g. 80).
- CdA. This is the metric of aerodynamic drag (Coefficient of drag x frontal Area) applicable to the rider and bike combined.
The figure is expressed in metres squared. Typical cycling values are in the range .20 to .30
- Tyre Radius. Input the radius of your wheels (including tyres) or simply use the dropdown to select one of the popular values.
- Wheel Intertia. This is a hard to measure coefficient. It is suggested to retain the default of 12.
- CRR (Rolling Resistance). Select the coefficient of rolling resistance applicable to the course. The dropdown is a handy way to select typical values.
Quote Power At / Drivetrain Efficiency
Power meters such as the SRM, Quarq & Ergomo measure wattage at the cranks. The actual wattage delivered to the hub, where a PowerTap would measure it,
is a little bit lower due to drivetrain inefficiencies. Specify drivetrain efficiency in percent (eg 97.5, which would be a good estimate).
The significance of this parameter is that, if the model is set up to calculate the power required to achive a particular time on a particular course,
the power required of the cyclist will be a little higher if quoted at the crank. ie 97.5 watts required at the road = 97.5 watts at the at the hub =
100 watts at the crank, when drivetrain efficiency is 97.5%.
Course Sectors
- Direction. Select the applicable direction as heading (e.g. NW) or else input a bearing between 0 and 255 degrees. This relates the riders direction to the wind, so a
ride direction of "S" (180 degrees) is an unmitigated headwind when the wind direction is "N" (0 degrees).
- Distance (KM). Input the ride distance in kilometres (e.g. 40).
- Average Grade (%). Input a gradient in percent (e.g. 3 is 3 percent, -2 is -3 percent).
- Input. Select a choice of input from Power, Speed, or Time.
- Power (Watts). Input the sector power in watts.
- Speed. Input the sector speed in KPH.
- Ride Time. Input the sector time in minutes and seconds.
If you have loaded a predefined course (public or attached to your profile) then mousing over the sector number (e.g. "Sector 1") will display the sector name.
Outputs
- Average power over the course.
- Average speed over the course.
- Total time over the course.
- The time to mid distance which may be of interest to time triallists contemplating split times, especially on out and back courses.
Air Pressure Scenarios
Outputs specific to air pressure analysis are covered above.