Originally Posted by Picchio Special

Most true racing bikes have used 700C wheels for a long, long time. Up until the availability of good clincher wheels - and even beyond - most of these bikes originally had tubular wheels. Bikes with 27-inch wheels used clincher tires, but were generally not true top-line racing models. Many were designed for recreational use or touring. So the answer is, if it's a good-quality frame built for racing, it was in all likelihood built for 700C wheels.