Andre Jute wrote:

Let's be clear. A bicycle with tyres of less than 57.5mm nominal width
is not a 29er. A bicycle with rims so narrow that any tyres, including
nominal balloons, have to be pumped up to high pressures to stay on
the rim and not to be dangerous at speed, is not a balloon bike, and
therefore not a 29er.

A corollary of your reasoning here would be that the same principles
define 26" MTBs. Since by 1990 most high-end MTBs sported narrow rims
that wouldn't pass muster according to your standards, they aren't
MTBs by your reasoning. But they are.

In my book, any bike whose frame will fit 700x50 (actual) tires or
larger without the tires rubbing hard parts when ridden is a 29er.
Doesn't matter what rims are on it.

Chalo