Treadmill or bike - Calorie question

akmfp

Quick question, have a total lack of understanding regarding exercise and calories. My exercise bike says that I am burning approx 250cal per 30 minute session (on toughest setting and a steady pace of 35/40kph). Litterally do not build a sweat and cannot feel any affect to my legs. However same 30minute session on the treadmill running at 8kph claims I am only burning off less than 100 and I am literally sweating and can feel the pain on my legs. Is my exercise bike lying? I am wondering why I even bother with the treadmill if I am burning off 250cal per 30min on bike with little effort?