I've been doing some research trying to figure out which is the better cardio workout. On my bike I average I'd say a good 20-25km/h (fairly hilly path with some offroad, very windy on some parts) for an hour (I'm not actually sure the exact distance of the route but I'd say it's a good 20+km). How does this compare to running? The conversion I've always assumed was 20km cycling=5km running but that of course could be totally wrong.