Originally Posted by
Road Fan
I agree, the term is pretty old. I don't know when I first heard or saw it, but I think it was in the first half of the 1970s.
I first came across Q-factor in the 1990 Bridgestone catalog. Grant Peterson, chief Bridgestone designer, claims to have coined it. Here's his explanation.
https://pedalchile.com/blog/q-factor
Of course, in 1990, 126 or 130 mm rear axles were de rigeur, so there was no need to go too wide.