Earlier this summer there was a similar accident, although not at such a
slow speed, in one of the bike clubs I belong to. A rider with a new
disc brake bike, the group turned onto a major highway with a very tiny
shoulder, something happened with the traffic up ahead, she put on her
brakes hard and went flying over the handlebars, breaking her wrist.
I have but very limited experience with disc brakes, mostly from one
ride where I swapped bikes -- my AM Moulton, his townie e-bike -- while
we were riding together on the W&OD Trail, in the East Falls Church
section where there's an at-grade crossing every block. It drove me
nuts. The stop line is so far back from the curb cut you don't have a
good sight line to either left or right, so my usual approach is stop at
the stop line, give it a little pedal stroke to get rolling and roll up
to the curb cut. If it's clear, I go; if not, I stop. On his e-bike,
one little pedal push and ZOOM I was right in the middle of the
intersection. (A mechanic at my LBS told me some e-bikes have their
most powerful reaction to just such a slight pedal push, and it takes
some getting used to to control it.)
But the brakes were far more disconcerting. All the rim brakes I'm used
to have some slack. Approaching a possible braking situation, I'm used
to taking up the slack and feeling for the friction point where braking
starts, so if I need to I can brake instantly. When I tried that on the
borrowed e-bike, the disc brakes locked instantly and I never felt any
friction point at all. Reminded me of a 1973 Chrysler with power brakes
I drove once: brakes so over-sensitive if you blew on the brake pedal
you'd lock the wheels.
So sure, I can see how a crash like that could happen, especially if the
rider was genuinely trying to stop very quickly. Full bore squeeze
without assuming a braced position and you can get the back wheel of
just about anything except a tandem off the ground.
On 11/1/18 3:10 PM, Ash wrote:
I've been wondering how in the world a bike can simply flip at slow
speeds. That too, on a flat road. I'm beginning to think the combo
of disc brake and short wheelbase might have something to do. In my
limited experience with discs, my impression is that they can be much
sharper relative to rim brakes. They are perhaps less forgiving on
someone not experienced in biking. Someone who does not have a feel
for how much to sqeeze the front brake vs the rear. Once the front
wheel is locked, an SWB is more likely to flip over than, let's say,
an Appa or Clem, I'm thinking.
--
Steve Palincsar
Alexandria, Virginia
USA
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