khutch

First, I would suggest that you look at the Marin Lombard. They may have a dealer near you, some REI stores are able to carry them too. It might be very close to what you want.

Putting wider tires on depends on two things, the rim width and the frame width (and sometimes other frame clearance dimensions). Sheldon Brown has a rim width compatibility chart towards the bottom of this page that gives some guidelines on which tire widths fit which rim widths. He notes that you can exceed the recommendations somewhat. My Fuji came with 14 mm rims (conveniently not on his chart) and 28 mm tires. I am currently running 32 mm tires on it which seem to work fine and may try 37/38 mm tires. You might have to get a new set of wheels with wider rims or rebuild the wheels you have with wider rims if your rims are narrow and you want to put very wide tires on them.

Ultimately the frame has to clear the tire width. You can judge that pretty well by looking at how much clearance you have with the present tires. Keep in mind that wider tires are also taller tires and in some cases you may not have enough clearance on frame crossbars, forks, etc with very much wider tires. Again you can judge this reasonably well by looking at the tires you have. The increase in height is approximately equal to the increase in width.

Ken