racerfern wrote:Should the sum of the average wattage of (Aero + Rolling + Gravity) equal the average power of the ride? Should it be close? How close? If it is not the sum of the three, what affects it to be different?
The sum of aero, rolling, and hill should be very close the average propultion power, which is power / Cm, where Cm = 1.02.
However, there are some other factors to consider. Some of your propultion power goes into braking, so if you have a ride with a lot of stops that can add up. You can get the average power of your braking by dividing the braking energy in Joules by the number of seconds in your ride.
For example, take the stats from the following ride.
Code: Select all
Dist: 22.61 mi (1:06:44)
Energy: 918.5 kJ
Cals Burn: 878.1 kcal
Climbing: 807 ft
Braking: 5.3 kJ (0.6%)
Min Avg Max
Power 0 229.4 855 W
Aero 0 163.8 1062 W
Rolling 1 58.9 97 W
Gravity -1016 0.9 758 W
Speed 0.4 20.3 33.5 mi/h
Wind 2.1 20.5 34.1 mi/h
Elev 223 268 327 ft
Slope -8.6 0.01 10.6 %
Caden 6 77.1 104 rpm
HR 94 161.1 173 bpm
Aero: 0.326; Fric: 13.52
CdA: 0.350 m^2
Crr: 0.0070
208 lbs; 7/27/2008 8:13 AM
75 degF; 1011 mbar
Average Propultion Power = 229.4 W / 1.02 = 224.9 W
Average Braking Power = 5300 J / 4004 s = 1.3 W
The losses add up to
163.8 W Aero
58.9 W Rolling
0.9 W Hill
+ 1.3 W Braking
--------------------
224.9 W Total
So in this case the numbers match up; however, normally there is some difference. Part of that might be due to the power that it takes to accelerate. For example, if you start the ride file from a stop but press the ride reset button while you are still rolling at the end of the ride (and therefore the braking power is short) then there is a net positive "inertia power". The shorter the ride, the more noticeable this would be.
And on top of all that there is still some proprietary secret sauce in the power balance sheet. As you can see, it didn't come in significantly in the ride above; however, sometimes it can be a couple of watts for some riders.
Travis