Originally Posted by
halfspeed
In the grand scheme of things whatever performance differences there are between 26" and 700c wheels are small enough to be of no consequence to a touring rider. Consider that tri bikes for many years ran 650c wheels sacrificing a small amount of rolling resistance in favor of improved aerodynamics. Also consider that recumbents, the absolute fastest way to travel on two wheels, use all sorts of different wheel sizes. Even on the same bike! A Moulton folder with wheels smaller than 26" was used to set an indoor HPV record.
Equivalent 26" wheels are marginally stronger lighter and more aerodynamic than 700Cs even though they have slightly more rolling resistance. They'll be a little less comfortable, but that can be compensated with slightly wider tires or lower pressure which may slow them back down a bit. As a practical matter, it's a wash.
So why should you choose one or the other?
1) Fit. A smaller rider should use smaller wheels because the frame geometry has to be compromised to fit 700C wheels in a smaller frame.
2) Tire availability. If you're doing extended touring in the third world you'll have an easier time finding spare tires in 26" size.
Most of the rest of the brouhaha on this issue is pointless. You're straining at gnats.
Thank you.
Given the differences in purposes -- 700s are generally for road, 26 are generally for off road -- probably the biggest difference is the selection of tires. Otherwise, if you want to go faster, work on the engine.
BTW, the Schwalbe website is excellent. If you want to understand why a wider tire can have less rolling resistance than a skinny tire at the same tire pressure, there are some pretty pictures that demonstrate the point. Although, as Sheldon wrote, the ceteris parabis argument breaks down once you realize that skinny tires almost always run at higher tire pressures.