This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Jobst Brandt <email@example.com>
Date: Tue, 04 Nov 1997 14:33:14 PST
> Should I continue to turn my bicycle upside-down to fix a flat,
> the way I learned it as a youth?
Nothing can be done to a bicycle upside-down that cannot be done
better with it right-side-up, except to spin the rear wheel while hand
cranking the pedals. In fact, that is what most children do when they
haven't anything better to do with their bicycles. That is how I
discovered that a bicycle wheel is not well balanced, because the
bicycle began to hop when I cranked fast. I also found that this wore
a hole in the saddle, and scratched the handlebars and grips to the
dismay of my parents.
Many riders who have taken up the sport after years off the bicycle,
recall only a few things from their earlier experience, and turning
the bicycle upside-down seems to be one of them. I defy someone to
show me how they can change a rear wheel easily on an upturned
bicycle, be that with one speed or a derailleur. Even chain removal
is more difficult on the inverted bicycle, but this should be apparent
because no bicycle shop works on upside-down bicycles.
Beside the inconvenience, damage to the saddles, handle bars, and
speedometers is expensive. Warranty claims for damaged speedometers
with cracked LCD's and housings first brought this practice to my
attention, the failures being unexplainable under normal use. The
solution was to reinforce the speedometer's case so it could support
the load of the bicycle.
The most common explanation for this practice is that there was no way
to keep the bicycle from falling over during a tire change. Laying it
on its side somehow doesn't seem right, so the bicycle is turned on
its head. It might not look fallen over, but it is worse off.