I am 80 pounds overweight and just purchased a cheap bike. I live very close to work but I plan on riding the bike for my commute. 5 miles roundtrip everyday at a leisurly pace (let's face it, who's in a hurry to get to work) probably will not help me lose any pounds. How much more riding should I do? 10 miles? 15? My goal is to lose enough weight so that I can start to run some more (my knees hurt to badly now). I would also like to tone my legs up, as they rub together a bit now when I walk (sorry to gross people out). Will riding a bike help to tone the upper/inner thigh area?