I am 5'7, 145lbs. I want to loose weight and tone my butt and back of my legs. I love to eat. I try to eat mostly healthy food ie; low fat, low sugar foods. I take a multivitamin and drink plenty of water. I haven't been riding a bike long, but I would like to know about how long and/or fast I need to go and how many days a week in order to really get my butt into shape and not have to starve myself. I do some weight toning about 2x a week. I ride 2-3 times a week, 3-5 miles each day. What device can I get on my bike to tell how fast I need to go?