Here's an idea that might lead people to share their recent rides; thus, leading to more people joining Strava.
The idea: a side-view profile of the route you road. This would look like the hill profiles used in the TV coverage on professional bike races, which shows the major climbs on the route, which has a rating at the top of each hill (HC, 1, 2, 3, etc). Aside from a cool perspective on your ride, I suspect people would share these images with others. ("Check out the tough route I rode today.")
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