Originally Posted by
ronin4740
On that subject I'm not sure why a Garmin head unit couldn't calculate power when it's paired with a Di2 system - I'd think knowing the number of teeth on the chain ring and cassette + the cadence of the cranks + the position of the chain would be sufficient to generate reasonably good power readings. Maybe I just don't fully understand how that's calculated.
Much more to it than what gear you are in and how much you and your bike weigh. You have rolling resistance, aerodynamics, terrain, wind, temperature, etc... Strava accounts for this but makes generalizations in their formulas, and it's still not accurate.