I bought my wife a Trek 7.2 FX last year and she loves it. I took her on a relatively beginner level single track last week and she had a blast, but the ride was a bit rough. Currently the bike has the stock 700x35c tires on it, and I am looking to throw something with more air volume and run it at a lower pressure to give her some more cushioning. I realize there isn't a whole lot of room in the front and back for a really large tire, but wanted to know how big some of you have gone. Could I fit a 42 or 45? Any specific tire that works really well? Thanks!