Wednesday, May 23, 2007

Ergomo Accuracy Check

Since I deal with wattage numbers a lot, I thought I'd use some numbers from a recent ride to check my Ergomo Pro's accuracy. I have no reason to doubt the numbers it's giving me, but a good real world check now and then makes sense.

The best way to calculate wattage is using data from a climb because air resistance becomes almost negligible at low speeds. Since air resistance is the most difficult to accurately measure (using friction factors and frontal area estimates), the smaller role that it plays, the more confidence I have in the calculation.

I used a wattage calculation spreadsheet to input bike weight, body weight, climb length, climb slope, air temperature, air friction factor, tire rolling resistance, drivetrain friction, rider frontal area, and power output (I entered the average power reading from the climb as measured by my Ergomo Pro).

I was amazed to find that the spreadsheet calculation for climb time matched my actual climb time (as recorded by my Ergomo) to the exact second -- 1 minute, 5 seconds. Later I performed the same calculation for one other climb on the same ride and it matched the calculation by 1 second. That satisfies me that my power meter is giving me good data.