Calculating power output

Nebhotep said:

I'm curious as to how(and if) I can calculate my power based on a time-trial I do.What information do I have to gather to find out?Thanks!

Temperature, humidity, barometric pressure, wind direction, and a topo map of the course. Go to www.analyticcycling.com
analyticcycling.comDiffEqWindCourse Page.htmlOpen ↗
Use the advanced input form and enter the course topo map information.
guess the power and change it until the calculated speed matches your speed.

Woofer said:

Temperature, humidity, barometric pressure, wind direction, and a topo map of the course. Go to www.analyticcycling.com
analyticcycling.comDiffEqWindCourse Page.htmlOpen ↗
Use the advanced input form and enter the course topo map information.
guess the power and change it until the calculated speed matches your speed.

you forgot the most important thing - frontal area. this affects power the most, while at speed.
the only way you can get much of an idea of your frontal area (without a powermeter), is to find a very steady long downhill, on a windless day, and coast done it in your TT position. using analyticcycling.com you can plug in the other variables to determine frontal area. you also need to go to topozone.com and accurately find out the exact grade of that hill.

even then, it's impossible to accurately determine power output unless you are on a dead flat road with no wind, or velodrome. typical roads vary in terrain way too much to make it possible.

IOW, you need a real powermeter - SRM, powertap. ergomo? polar?

also, I have a powertap, and i will get different average power outputs on the same course, for the same speed, during the same conditions. it all depends on how i pace myself. if i hammer up the hills, then coast the downhills, my average power will be less than if i held a steady effort the whole way, even with the average speeds being the same.