Originally Posted by
zacster
These devices aren't terribly accurate on grade. They are slow to react to changes. I'll be halfway up the Manhattan Bridge before it shows the change in grade. I thought Strava used geographic data though. I did a long ride up Mt. Haleakala in Maui a few years ago with a Garmin watch that didn't have a grade sensor but Strava still showed it.
Yes, Strava seems to take various data sources into account for grade, and when you use the phone app it apparently only looks at their own data, and not your phone's input (if it has a barometric sensor). Still, the grading for some portions of the 59th Street bridge climb is wrong (since it shows them as negative), and you would think they have tons of data to work with for a heavily trafficked place like that.
But I also see that several people are either riding on the regular roadway for cars, or keeping their Strava turned on while in the car (some of the record times/speeds are pretty laughable), so maybe it causes confusion because the roadways are slightly lower than the bike path?
I have to say the App is still a lot of fun despite these issues, as it's super interesting to compare my own commuting times and speeds based on the conditions and the bike I'm using.