I tried my friends GT mountain bike (size small) and it felt really big to me. I know that I am just used to my road bike, but I guess I am not really sure what the right fit should feel like. I went and looked at a Kona Cinder Cone size 16 and I think that is too big as well. I feel like I am in foreign territory here. My old mountain bike was very low end and hurt my knees terribly. I used it mainly to follow my kids around the neighborhood on their bikes. Now that they are bigger and are wanting to do more trail riding I need a better bike. I am just not sure testing them for a short ride around the parking lot will give me enough of a feel for what fit is right. Is there a general guide like with road bikes where the handle bars should cancel out your view of the front hub to give me an idea of what size might be right?