Cycling is a good exercise for weight loss but the real world numbers are a long way from cycling uses 30 calories per mile.
The table to the right says cycling on a RoadBike_Racer (Tops) for an hour @ 12MPH needs 61 watts and expends 209 kcals per hour.
But if you do the maths
61 watts is 61 joules per second
or 3,660 joules per minute
or 219,600 joules per hour
or 52,486 calories per hour
or 52 kcalories per hour
So where does this 209 come from?
The human body is not very efficient at converting eaten food to work done, it's typically assumed to be 25% efficient.