I just bought a Trek 7.3 and am curious if I can put bigger/nubbier tires on it? I‘m afraind to go riding on the CO towpath on the road tires it came with.
Sounds like you need some Cyclocross tyres, which are essentially a 700c tyre designed for both off and on-road use. Go to any tyre manufacturer website and look up their 'Cyclocross' range, and read the tyre description to see if it's got what you need. I put the Maxxis link below to give you an idea what I mean.
If you can find some that accomodate your rims, if not you might have to get wider rims
