Originally Posted by
Happy Feet
The problem with thinking modern 29r design was always around isn't regarding tire diameter, it's rim width. A modern 29r mtb tire won't fit a previously available 700c rim. Just like my 4.6" fat tires don't fit on standard 26r rims, even though they are nominally the same size.
The reason why it is difficult to fit some modern 700C/29er tires onto old 700C rims is because the modern tires are usually intended to be used without inner-tubes. The resulting extra tight fit can mean that you can break tire-levers whilst trying to fit them,
Despite this I have managed to fit two types of modern (tubeless-ready tires) onto my 1981, 700C, Geoff Apps Range-Rider off-road bicycle.