I am looking on craigslist for another bike. There was a Trek FX size 17.5 listed (44.5 cm). I am bad with sizing. Right now I own a LOOK road bike that is 50 cm, a Specialized Dolce that is 48 cm, and a Trek mountain bike that is a 16. Do you think the Trek would fit? I want to try an more upright bike as my road bikes cause some neck/shoulder issues and my mountain bike never does.