This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Jobst Brandt <firstname.lastname@example.org>
Date: Fri, 05 Sep 1997 17:31:23 PDT
Many bicyclists fear using the front brake because they believe it, in
contrast to the rear brake, might cause the bicycle to overturn. What
is not apparent, is that overturning a bicycle with the front brake is
much harder than it seems, and that braking itself, is not the cause
of most pitchovers.
The primary cause of bicycle pitchover, is that the bicycle stops and
the rider does not, after which the bicycle overturns when the rider's
thighs strike the handlebars. Overturning can be simulated by walking
next to the bicycle, both hands on the bars, and applying the front
brake to raise the rear wheel. This experiment should make apparent
how small a force will overturn the bicycle when it stops and the
rider does not.
Beginners overturn when they use the front brake because they are not
aware that, unless they brace with their arms, only the friction on
the saddle prevents the bicycle from stopping without them. However,
even riders, who don't make this mistake, can pitchover from a
front-wheel jam that leaves no time to react. A stopped rear wheel
usually does not cause pitchover, because even if the rider moves
forward, unloading the rear wheel, effectively releases the brake.
Typically, front wheel jams occur from a stick in the spokes, a fender
jamming into the fork crown, a front cantilever straddle cable falling
onto a knobby tread, or a retaining bolt of a caliper brake releasing
from the fork crown. These are unanticipated events for which a rider
cannot brace if not already doing so. However, on clean pavement a
front wheel jam will overturn the bicycle regardless of rider reaction.
That bicycles do not easily overturn by braking becomes apparent by
attempting to raise the rear wheel, preferably at modest speed and
while bracing with the arms. The front brake, the principal stopping
and speed control device on motorcycles and cars, is especially
important for bicycles, whose short wheelbase causes even more weight
to transfer to the front wheel while braking, thereby making the rear
brake less effective. Therefore, the front brake should be understood
and used properly rather than being maligned as it is.
Formerly bicycles in the USA had their front brake on the right hand
as do motorcycles. A concerted effort by right handed safety
advocates, moved the "dangerous" front brake to the left hand, where
it could do less harm, and there it remains today.