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Old July 16th 03, 04:56 PM
Daniel Connelly
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Default Braking Technique

asqui wrote:
Callistus Valerius wrote:
The argument I have heard is thus:

Since the center of gravity of the human-bike system is higher than the
wheel-road interface (which provides the braking force) the human-bike
system has the tendency to pitch forward with braking, causing weight
transfer to the front wheel.
Hence the theoretical scenario for maximal braking would be that the braking
is sufficient to transfer all weight to the front wheel, leaving the rear
wheel with zero force on the ground. At this point any increase in braking
force of the front wheel would cause the rear wheel to lose contact with the
ground, and braking on the rear wheel would cause the it to skid and
increase the chances of the rider losing control.

This assumes that the front wheel has sufficient friction with the road (in
order to not skid) and brake blocks (in order to receive the necessary
braking force).

As for the experiment, I've already carried it out -- steep downhill, amber
light, car in front stops. I managed to stop about a meter behind said car,
with my rear wheel off the ground and trying to overtake me. I think that
was because I was out of the saddle and didn't sit down on it properly as I
was braking. Ideally I would have sat down and shifted my weight back to
keep the rear wheel on the ground and increase my stability.

What do you think?


In real world conditions, uncertainty in the current state of the
system, plus time-variation in the conditions, means it's not possible
to brake at the theoretical limit. This makes it prudent to
apply rear braking force, as well. As the deceleration increases, the
normal force at the rear tire/road contact decreases, decreasing the braking
force relative to what it would be if only the front brake was used.
OTOH, if all force is applied to the front brake, an increase in the
normal force at the front tire due to a momentary increase in the rate
of deceleration will have maximum positive feedback as braking force
is then increased. Positive feedback is destabilizing.

Result: hospitalization.

Dan

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