Originally Posted by
wschruba
It's driven by an industry who can't decide how they want to market things, so generally speaking, inches refer to mountain bikes, French sizing to everything else. Mechanics use ETRTO sizes, as it leaves no room for miscommunication. 622, for those sizes, for what it's worth.
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When my new tyre fell over the rim, I found out that the classic inch sizes refer to the outer circumference of the wheel, including the tyre. So a classic 28" rim is about 27". ETRTO is the actual rim size and the inner circumference of the tyre.
