There is a distinct performance difference between 700c and 27". That said, I have to disagree with some of the comments or opinions of others. The 27". all things being equal, will feel somewhat sluggish when compared to the 700c offering. Why..?
Bicycle wheels, when spinning, become gyroscopes and the further the rim is away from the axle, the greater the gyroscopic effect. It is easy to understand the gyroscopic feel...
Take a bicycle wheel, any wheel. Hold it by the axle and, while keeping the wheel, more or less, vertical, tip if from side to side. Now, using the same wheel, give it a good spin and attempt to tip it from side to side. My guess is that the resistance to tipping will surprise you when the wheel is spinning. Now, double that effect, since a bicycle has two wheels, and you will know what a wheel with larger diameter rims has a more negative impact of ride feel. Also...
As others have suggested, tire selection for 27" wheels are, somewhat, limited and, in general, 27" tires and inner tubes tend to be heavier than their 700c rivals. The more weight one adds to the wheel rim/tire combination, the greater the gyroscopic effect. Hence, once again, the ride quality or feel in negatively impacted.
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