Okay I'm 17 and I'm overweight and want to loose the weight, now I'm planning to do bike exercising 3 times a week, and I be doing 3 miles there than 3 miles back so in total I be doing 18miles a week. What I want to know is I heard biking only good for lower body, so is this not going to loose weight I have on my upper body. Also is 18miles good a week?