HP NOTEBOOKS WEIGHT
How accurate are the radar speed indicator (K-band) on a quarter mile strip?
Yesterday, we had a fun day at the local strip where we tested our cars and my bicycle on quarter mile times. Since the system is connected to a notebook computer, it automatically logs the trap speed and the curb weight of our vehicles, and it calculates the horsepower as each participant has completed her run. I did three runs on my Cannondale and my approximated horsepower are as follows:
1st run (best run) = 0.221 hp (weight = 129 lbs, speed = 28 mph, elapsed time = 48.68 seconds)
2nd run = 0.198 hp (weight = 129 lbs, speed = 26 mph)
3rd run = 0.177 hp (weight = 129 lbs, speed = 25 mph)
Are the above figures accurate?
PS: Yin did an elapsed time of 14.24 at 96 mph in her Volvo C30.
Note: The strip is an old airfield, and a hand-held radar was used to measure the speed.
HI Kate
I doubt the power calculations are right. Your final trap speed should be a rough guide to the average power during the run. (most likely a bit lower.) For a cyclist (roughly your size) to do around 28 mph should take about .5 hp (conservative.)
I would suspect the computer is using automotive parameters to do the calculations. The most notable difference would be coefficient of wind drag (Cd). A typical car would be 0.26 -0.4, a typical cyclist 0.9.
http://en.wikipedia.org/wiki/Drag_coefficient
Basic formula for flat ground, no wind.
power(watts) = (1/2 * Cd * A * ρ * V2 + Crr * W ) V
Cd= 0.9 Many bikes will have a much lower Cd than this. Once a very non aerodynamic cyclist is added, the figure will wind up close to this.
A = Cross sectional area (average is about 0.4 sqr metres.) For a Petite Women about 0.34 M2
ρ= density of air. I usually go with 1.22 Kg/cubic metre but this varies with temperature and barometric pressure etc.
V= speed in metres/second. (28mph =12.5M/S)
Crr= coefficient of rolling resistance (0.004-0.006 road bike on a hard flat surface.)
W= weight in Kg
You will probably get a more accurate figure for power if you towed a car. Be careful using a snatch strap, taking off to quick could damage your bikes frame.
Footnote for JP
Most pro cyclists can peak over 1000 watts and maintain close to 400 watts (0.54 hp) for 30 minutes +
http://www.getoutdoors.com/goblog/index.php?/archives/1267-Wattage-Kick-Floyd-Landis-Ass-iBike-Power-Meter.html
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