Join Date: Jun 2004
Location: Northern Nevada
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Retro's right, but I'm going to differ on a couple of small points. My singlespeed is built from a Trek touring bike that came with 27-inch wheels, and when I swapped to 700c's (for a larger selection of tires, and because I had the wheels lying around), it was a straight bolt-on. All I had to do was lower the brake pads in the calipers' slots. Not all brakes have that much adjustment, though.
FWIW, rim width isn't usually the limiting factor in tire width. I've run tires from 23 to 41mm on the same wheels on a couple of bikes with no trouble. The space between the fork blades and under the rear brake arch are more likely to restrict you, and the slightly smaller-diameter wheels will give you more space there. My Trek would fit 1-1/4 inch tires with the 27s, but with the 700s, the 41mm tires have lots of room.
You CAN still get 27-inch tires, but the variety is pretty limited, and most shops that stock them have low-end tires for older, rarely ridden bikes. With 700c, you can get anything you want, from fatty knobbies to skinny time trial rubber.
Functionally I don't think there's any difference. You could invent theoretical benefits (the larger wheel rolls over obstacles better?), but they're so close it doesn't matter. My pref if I could swap without buying new brakes would be for 700s, for the range of tires. If I had to spend money on brakes, I'd stick with the 27s and never give it another thought.