This is quoted from the message board:
How do we measure power on a Hill CLimb site
posted by Andy Steven on the 26/03/2003
hill climbs
details:
A lot of people ask this question, so I thought I would explain it here.
The formula we use for calculating power is pretty easy:
0.1315 * (climb_distance/time)^3 + 9.81*(time_rider_kg + time_bike_kg)*ascent/time
so basically it is potential energy plus a factor of speed due to wind resistance etc.
The formula is very accurate on a steady climb with no flat spots on a wind free day, provided the ascent is known accurately.
for example a 70kg rider with a 10 kg bike riding at 20 km hour up a total ascent of 300m, distance is 5 km, in 15 minutes(15*60 sec)
Power= 0.1315 * (5000/900)^3 + 9.81*(80)*300/900
Power= 22W from wind + 261 W from potential energy
So as you can see, when climbing wind resistance doesn't count much, so if the ride has no flat sections (faster speed)and is a steady climb at 20km/hr or less the accuracy will be with in 5%, provided the ascent and weights are correct.
How do we measure power on a Hill CLimb site
posted by Andy Steven on the 26/03/2003
hill climbs
details:
A lot of people ask this question, so I thought I would explain it here.
The formula we use for calculating power is pretty easy:
0.1315 * (climb_distance/time)^3 + 9.81*(time_rider_kg + time_bike_kg)*ascent/time
so basically it is potential energy plus a factor of speed due to wind resistance etc.
The formula is very accurate on a steady climb with no flat spots on a wind free day, provided the ascent is known accurately.
for example a 70kg rider with a 10 kg bike riding at 20 km hour up a total ascent of 300m, distance is 5 km, in 15 minutes(15*60 sec)
Power= 0.1315 * (5000/900)^3 + 9.81*(80)*300/900
Power= 22W from wind + 261 W from potential energy
So as you can see, when climbing wind resistance doesn't count much, so if the ride has no flat sections (faster speed)and is a steady climb at 20km/hr or less the accuracy will be with in 5%, provided the ascent and weights are correct.