Before you shell out for new shoes, get some medical advice. I had this problem, and thought I also had shin splints, but it turned out to be 'chrionic anterior compartment syndrome' and I need very carefully designed inserts for all my shoes (as well as a myriad of other treatments). If you try the one leg cycling thing, and find your shins hurt or the muscle down the front aches, this might be a reason...quite common in pronators apparently. Pain in your shins when you're standing on the pedals (climbing) is another sign. Another possibility is restricted blood flow in your femural artery when you're on the bike. A doctor can find this quickly by listening to the blood flow in your hip joint when you're in a cycling like position. Worth checking out!