[oldalum]

30 feet is probably ridiculously safe. But the study referenced in the preprinted study discussed in the link above found a trail of particles 30 feet behind a cyclist going fast, which makes sense because it only takes a couple of seconds for a cyclist to traverse that distance at that speed. What I found interesting in the aerodynamics study is that the trail left behind a fast cyclist is only as wide as his or her shoulders.I wouldn't ride right behind another rider, you're inhaling too much of what they are exhaling.  And I wouldn't run right behind another runner, either. 

[oldalum]

30 feet is probably ridiculously safe. But the study referenced in the preprinted study discussed in the link above found a trail of particles 30 feet behind a cyclist going fast, which makes sense because it only takes a couple of seconds for a cyclist to traverse that distance at that speed. What I found interesting in the aerodynamics study is that the trail left behind a fast cyclist is only as wide as his or her shoulders.I wouldn't ride right behind another rider, you're inhaling too much of what they are exhaling.  And I wouldn't run right behind another runner, either.