I asserted:
Quoted message said:Quoted message said:You may not have ridden a coaster brake bike lately, and I
don't blame you, but the ergonomics of it permit you to
get your weight farther back when you can put your whole
weight on the rear pedal, rather than having to balance it
between the two pedals, as you need to do with a
freewheeling bike.
Jim Adney said:
If you move your butt backwards off the saddle when you
backpedal a coaster brake then you're certainly moving
your center of mass rearwards, but I don't think that's
what many people do.
That is the way you do a panic stop on a coaster brake.
Quoted message said:As long as your butt doesn't move, your CoM didn't move
significantly, and the weight distribution on the bike
didn't change.
That's certainly correct.
Quoted message said:I get the impression that you're thinking that all the
weight must be either over the bottom bracket or over
the rear wheel, but you're forgetting that there are
some contact forces on the handlebars and maybe some on
the seat.
In the maximum-braking case I refer to, the rider would not
be on the saddle, but would probably have a locked knee on
the braking leg.
Quoted message said:Plus it's important to note that forces on the pedals need
not be strictly vertical since the hands and arms can make
up for significant force in this direction.
That's true, but those components can apply either way.
Quoted message said:All of which can happen without any significant movement
of the CoM.
But, this is testable!
Put your coaster brake bike in a doorway and put one wheel
in a normal bathroom scale. Put a book of the same
thickness under the other wheel. Now hold yourself up in
the doorway, being careful to exert minimal force on the
doorway (or get someone else to do this for you.)
Read the scale while pressing hard on the coaster brake.
Read it again with no pedal force (simulating coasting.)
I don't expect there to be any change in the readings
unless you slide off the rear of the saddle.
I'd agree there.
Quoted message said:Hmmmm..., IIRC, there IS a coaster brake bike here. My
daughter's old bike is small, but it would serve the
purpose.
I'll try to do this. You try it, too.
There are also dynamic aspects to this, because one can
bounce up and down a bit on the rear pedal, so this test
might not be altogether conclusive.
I don't have an accessible, working coaster brake bike. My
old Elgin is buried deep under the front porch, and last I
knew the New Departure brake had become unreliable--that's a
good part of the reason it got stuffed into the under-the-front-
porch morass...
I'm working from 50 year old memory here, when I used to
bomb around Marblehead on my old 24 inch wheel Rollfast, and
liked to do "Brodies" on it...
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