A runner friend of mine told me that you can calculate (very roughly) the calories burned during a run by multiplying one’s weight in Kilograms by the distance in Kilometers.

Does anyone know of a similar formula for bike riding? I realize that speed plays a role in both sports, but we’re talking good hardy training (bike average speed of 26 km/h (15.6 mph).

On a similar note, I saw once a bike/running comparison which said that a distance ratio of 5 to 1 would result in about the same work-out. Since the Tour de France riders regularly do 200km, by this calculation they are effectively doing the effort of a marathon (42km) twenty days in a row! We all know that the TdF is the height of endurance sports, but this ratio seems way off to me. My friend and I thought 8 to 1 sounded much better. Any opinions?