jeneralist 

From discussions on web pages like cyclingabout.com; from some custom bike manufacturers who make bikes with either 700c or 26" wheels, depending on user preference; and from other threads in this very forum (for example, https://www.bikeforums.net/showthread...00C-vs-26-quot)

Even though I live in the US, I'm not a big fan of the inches/pounds/pints "system". Any time a US system measurement becomes common in the metric world, I wonder why.

Machka 

Well, not to worry ... if you're toying with the idea of cycling in Europe, you should be able to find 700c tires.


Regarding the 26" tires ... my impression has always been that they are mtn bike tires ... generally wider than the 700c tires would be, often with more tread, and designed for "trekking" on unpaved roads and tracks. For whatever reason, mtn bike measurements have tended to be imperial ... even for things like frame size.

Pedaleur

In general, mountain bikes are measured in inches, because the mountain bike craze started in America. Road bikes used to be measured in inches, but have mostly switched over to metric due to European influences. Of course, many things you buy in 'metric' are just translated inches (eg, handlebars come in 25.4mm or 31.8mm, otherwise 1 1/4").

The really weird part is that in many parts of Europe, road wheels and tires are refered to at 29", and sometimes 28".

The link to Sheldon Brown's site above has good info on the conventions.

One more reason to consider 26" wheels is frame geometry. As the frame gets smaller, 26" wheels make it easier to have reasonable angles and tube lengths. Surly, for example, only makes the Long Haul Trucker with 700C on their 52cm frames and above. If you're short (under 5'8" or so?), you might consider 26" for that reason. But it's not a hard and fast rule or anything.

tcs

Tire diameters are just tire diameters.

26 inch (ISO 28x559)
700C (ISO 55x622)

Machka 

Yes, of course ... but generally 700c tires are used on road bicycles and 26" tires are used on mtn bikes. Touring bicycles may have some crossover between the two depending on the type of touring a person wants to do.

ttakata73

I live in a pretty half-assed part of the world.
Bangkok has money so we get 700c bikes and spares no problem, but when you head out to the countryside and the neighboring countries of Laos, Vietnam, and Cambodia almost everything looks like a Walmart grade of bike so they have 26" tires.
For anyone touring rural SE Asia I would recommend riding 26".