I have both on my Miyata. The bike came in(ebay sale) with a 27" rear wheel and a 700c front(both Araya rims). It's an '81, so I assume there was a problem with the front rim at some time, and a replacement was ordered in 700c and was drilled for a presta valve. I just carry an adapter for the presta in my under seat bag. Besides, the 27" rear is a bit taller than the 700c front rim, so I get the boost of always pedalling downhill!