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if you wanted maximum braking, where would you sit?



 
 
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  #1  
Old January 8th 04, 12:33 AM
wle
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Default if you wanted maximum braking, where would you sit?

if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be?

obviously over the front wheel is no good, you would flip.

there is a point, leaning either ahead of the front wheel, or
behind the back wheel, that the opposite wheel is off the ground.

clearly those are 2 limits, the answer must lie between them.

if there were very little friction, it would hardly matter.

assume a level road, brakes that can cause a skid no matter what.

ok, so where do you sit?

state assumptions, like coefficient of friction between tire and road,
weight of bike and rider.

show your work.

now for extra credit, make it a function of road slope.

wle.
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  #2  
Old January 8th 04, 01:21 AM
Rick Onanian
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Default if you wanted maximum braking, where would you sit?

On 7 Jan 2004 16:33:02 -0800, (wle) wrote:
if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be?


On a flat piece of rubber in direct contact with the pavement.

wle.

--
Rick Onanian
  #4  
Old January 8th 04, 01:54 AM
Tom Sherman
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Default if you wanted maximum braking, where would you sit?

wle wrote:

if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be?

obviously over the front wheel is no good, you would flip.

there is a point, leaning either ahead of the front wheel, or
behind the back wheel, that the opposite wheel is off the ground.

clearly those are 2 limits, the answer must lie between them.

if there were very little friction, it would hardly matter.

assume a level road, brakes that can cause a skid no matter what.

ok, so where do you sit?

state assumptions, like coefficient of friction between tire and road,
weight of bike and rider.


I would sit near or below the level of the front axle to reduce or
elminate the tendency for the rear wheel to lift off of the ground, and
I would also be near the rear wheel for more favorable weight
distribution for braking. This describes a recumbent lowracer. Braking
can be improved by adding a second wheel in front (tadpole trike) as
weight transfers forward to two contact patches during braking, and
locking one or both front wheels under braking will not lead to a loss
of balance.

Tom Sherman - Quad Cities

  #6  
Old January 8th 04, 04:06 AM
Mike Beauchamp
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Default if you wanted maximum braking, where would you sit?

I find the idea position changes depending on speed and deaccelleration
while breaking.
So, that means it's constantly changing...
It's hard to put into words actually, so I'm trying to think about it..

First of all, I wouldn't "sit" anywhere. I"d definately get out of the
saddle, but I'd stay very low. I'd apply the breaks lightly and fairly
evenly with more front than rear. Then, I'd increase pressure and the
faster I de accellerate the farther I'd slide my ass (which is still off the
seat) rearwards. Under the heaviest breaking, Ideally my weight would
probably want to be above the rear axle althought I doubt I could get it
that far back on even ground.

While breaking, I think it's impossible to lean far enough back where you
would not put enough weight on the front wheel (which should do the majority
of the breaking). So, when you're leaning as far back as you can under the
hardest breaking you're putting your physical weight onto the rear wheel so
you can break with that better than normally, plus because of the
deaccelleration a LOT of weight is still on the front wheel so you can get
as much out of it as well.

Mike
http://mikebeauchamp.com

"wle" wrote in message
om...
if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be?

obviously over the front wheel is no good, you would flip.

there is a point, leaning either ahead of the front wheel, or
behind the back wheel, that the opposite wheel is off the ground.

clearly those are 2 limits, the answer must lie between them.

if there were very little friction, it would hardly matter.

assume a level road, brakes that can cause a skid no matter what.

ok, so where do you sit?

state assumptions, like coefficient of friction between tire and road,
weight of bike and rider.

show your work.

now for extra credit, make it a function of road slope.

wle.



  #7  
Old January 8th 04, 04:24 AM
Steve Juniper
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Default if you wanted maximum braking, where would you sit?

Well, for maximum braking power you'd want to have max power for both
wheels. Because the rear tends to lose braking power as weight shifts
forward, moving back just far enough to balance the effect ought to produce
the max. I suppose you could tell where that is by trial and error,
determining how far back you need to move so that both wheels skid at the
same time.

No, wait a minute - on reflection it seems moving back would reduce front
braking power. Maybe it doesn't make any difference at all, so long as both
wheels stay on the ground or, theoretically, maybe not even then, until
braking itself causes the rear wheel to lift.
--
Steve Juniper

"Donald Rumsfeld took that job as Secretary of Defense because
he couldn't get a job with a death squad."
-- Barbara
Bush --

"wle" wrote in message
om...
if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be?

obviously over the front wheel is no good, you would flip.

there is a point, leaning either ahead of the front wheel, or
behind the back wheel, that the opposite wheel is off the ground.

clearly those are 2 limits, the answer must lie between them.

if there were very little friction, it would hardly matter.

assume a level road, brakes that can cause a skid no matter what.

ok, so where do you sit?

state assumptions, like coefficient of friction between tire and road,
weight of bike and rider.

show your work.

now for extra credit, make it a function of road slope.

wle.


  #10  
Old January 8th 04, 04:55 AM
Sheldon Brown
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Default if you wanted maximum braking, where would you sit?

Tim McNamara wrote:

Under "maximum braking" the front wheel stops dead, the bicycle
flips, and the rider is ejected. If you are talking about keeping
both wheels on the ground that is far less braking force than
maximum.


That can be circumvented. Build a bike that positions your center of
gravity below the front axle. You could lock the wheel up tight and
still not do an endo.


It actually has nothing to do with the axle, since a locked-up wheel
doesn't rotate, so it effectively stops being a wheel.

The critical thing is the angle of a line drawn from the tire contact
patch to the center of mass of the bike-and-rider.

If this angle is steeper than a critical value, locking up the front
wheel will cause an endo. This is the case for typical upright bikes.

If the angle is shallower than the critical angle, locking up the front
wheel will cause it to skid. This is the case for tandems and many
recumbents.

The value of the critical angle depends on the coefficient of friction
between the tire and the road surface.

For vehicles where the angle is steep, the rear brake is useless at
maximal braking.

For vehicles where the angle is shallow, both brakes are needed to
achieve maximal braking.

Note that the _length_ of the line doesn't matter, only the angle.

See also http://sheldonbrown.com/brakturn.html

Sheldon "Geometry And Physics" Brown
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