What pastorbob said is correct. I rode my 1972 Mondia for years with a set of 27" x 1 1/4" tires . It was nice being able to fly through sand or soft dirt roads but the bike felt sluggish on the road , where over 90% of my riding is done. I found a set of Super Champion 700c wheels and mounted some 700 x 25 tires and the bike now feels like my others .It is more responsive and I still can manage a bit of dirt when needed. I still run clinchers but the difference was amazing! Joe
This is how I rode this bike with heavy tires
with the 700c wheels and 25mm tires, it feels like a different bike!