in the summer i commute to/from work 3 times a week on my bike. It is 50km (31 miles) one way. So i ride to work monday, home wednesday, to work friday type of thing.

This trip takes me around 2 hours and people think i am crazy for doing this.. but those same individuals will spend an hour commuting and then go to the gym for an hour?

Cycling isnt suited to a few miles.. I have never been "athletic" and can do a 50KM ride with a bit of training.

If the ground is fairly flat i'd say 10 miles is reasonable.