Joined: Jan 2009
Posts: 44,222
Likes: 6,477
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
The GPS app (cyclemeter on iphone) and the Garmin GPS (Edge 200) I have used do make errors. I can't say the extent of the errors. You could probably use a web page and paint your route along the road and see what kind of estimate you get.