Hello, I am new here. I recently purchased a used Trek Mountain bike and have been riding it daily on asphalt about 5 miles a night. I was thinking about purchasing a quicker bike, possibly a road bike, but I also want to get that full exercise effect so I am considering a hybrid bike. My first goal in bike riding was to lose weight. Does anyone have any suggestions or should I try to change the tires on my existing bike? I really would appreciate your advice.