Working on a vintage bike recently I wanted to rebuild this as close as possible to the original version, with one exception, the wheelset.
The bike came with 27" wheels with high quality Araya alloy rims and Sunshine hubs. Very good but the rim edges where the tire meets the rim are straight with no lip to hold a modern clincher tire bead. Most 27" tires only allow 90 psi max. I had mounted Panaracer Pasela 27" tires on these rims and they worked well. The rear wheel had a flat spot, but not noticable except on fast descents. The straight edge rim of 27s left me wanting me to be able to run a tire at 95-100psi that with these rims might be a problem. I rode this pair of 27" wheels with the Paselas over Ebbetts Pass in the Sierras and on a few others rides without a hitch. But to my shock I saw the 27" rims had no lip after fixing a flat. For tires, you really don't want to mess around, so this was the main reason for switching to a modern 700c wheelset As a replacement, I had built-up a new wheelset with some NOS Maxi CAR high flange hubs and of Mavic Open Sport rims. These are fantastic riding wheels.
The 700c (622mm) wheel diameter is shorter than 27" (630mm) but easily adaptable to most bikes that originally came with 27" wheels. I've upgraded a few bikes with 27" wheels to 700c that allow much more of a range in tire widths and tire types.
Plus you can use tubes with lightweight presta valves that are better suited for road bikes than schrader style valves commonly found on 27" and MTB wheels. © 2011 VeloTouriste.