Bicycle Stopping Distances

MagillaGorilla wrote:
" wrote:

On Nov 2, 2:45 pm, "marco" wrote:
bjw wrote:
The calculator is wrong because they did not
consider that a bike's braking ability is limited
by going over the bars.
...snip...
However, everyone who thinks about this says that
a bike can't do that because of the high center of mass.
Most people agree that just from geometry (height of
the center of mass relative to how far forward the front
wheel contact patch), a bike is limited to at most
0.6 g deceleration, or 5.9 m/s^2.
A naive dynamics question: isn't it possible to modulate the front and rear
brakes to offset the high-center-of-gravity problem? Without really thinking
about it, that's what it feels like you do instinctively when trying to stop
really quickly. And of course you also push your weight back as much as you
can.

So no, a bike cannot stop faster than a car.
Somebody should do this test and post it on youtube.
No, you can't get extra braking power from the rear brake.
Braking transfers weight forward, as we all have felt;
another way of thinking about it is that the deceleration
of your center of mass generates a torque which wants
to pivot the bike forward around the front contact patch,
and the force of gravity pulling you down is what
counteracts that torque.

The limit of about 0.6 g is when the bike is just about
to start pivoting about the front contact patch by lifting
the rear wheel. At that point, it doesn't matter what
you do with the rear brake because there's almost no
weight on the rear wheel, so no friction. If you grab
it hard you may skid the rear wheel.

When trying to stop quickly, I grab both brakes, but I
think the rear is psychological. If your brakes are weak
or squishy or the road is wet, grabbing both may help.
I don't like braking real hard on the rear because it
skids - if you hit a wet patch or a bit of sand on the
road, very easy to skid and lose it. As Anders said,
newbies never get this right. It's tough to brake hard
enough on the front to endo, unless you are MTB'ing
and drop the front wheel into a rut or hole.

BTW, the 0.6 g number isn't magical, it's just based
on the angle from your center of mass to the front
contact patch. If the center of mass is around your
belly button, then (on my bike) the height off the ground
is about 1.2 m and the horizontal distance to the
contact patch is about 0.75 m. The geometry of the
opposing torques from deceleration and gravity means
that the bike starts to endo when the deceleration is
more than (0.75/1.2) ~ 0.63 g. All fairly approximate.

Ben

Hey dumbo,

In a maximum braking effort, you transfer your weight as far back and as low as
possible. You bury your head into your stem...you even your pedals so no leg is
higher than it has to be....you push your entire center of mass down into your
top tube. All of this is done instinctually and in a fraction of a second. So
all your numbers are wrong.

What you are talking about is the physics of how a ****ing Cat. 5 girl brakes her
bike on the Saulsalito Kenny Pap Smear group ride and then crashes into 6 riders
in front of her while claiming she "couldn't stop in time."

You mean when tuba players run over a girl's neck.



That's not how I stop my bike if I need to dig deep into the pro suitcase of
courage.

In fact, I would say a good proportion of maximum braking effort comes not from
how hard or quick you pull on the brake levers, but how quickly, how low, and how
rearward you shift your weight.

Your equation treats one of the most important aspects of maximum braking (i.e.
the lowering and shifting of center of mass rearward) as being a constant instead
of a rather large variable. That's the fundamental mistake of your equation.

You wrote the equation for how Liz Hatch stops her bike, and not for how the
monkey stops his bike.

QID.

Magilla

Anton Berlin wrote:
On Nov 3, 6:48 am, Susan Walker wrote:
Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.
Depends.

Sorry Susan but even if an old person craps in their Depends it still
falls at9.806 65 m /s^2 exactly

It depends. g0 is meaningless.

On Nov 4, 5:29*am, MagillaGorilla wrote:
" wrote:

BTW, the 0.6 g number isn't magical, it's just based
on the angle from your center of mass to the front
contact patch. *If the center of mass is around your
belly button, then (on my bike) the height off the ground
is about 1.2 m and the horizontal distance to the
contact patch is about 0.75 m. *The geometry of the
opposing torques from deceleration and gravity means
that the bike starts to endo when the deceleration is
more than (0.75/1.2) ~ 0.63 g. *All fairly approximate.

Ben

Hey dumbo,

In a maximum braking effort, you transfer your weight as far back and as low as
possible. *You bury your head into your stem...you even your pedals so no leg is
higher than it has to be....you push your entire center of mass down into your
top tube. *All of this is done instinctually and in a fraction of a second. *So
all your numbers are wrong.

What you are talking about is the physics of how a ****ing Cat. 5 girl brakes her
bike on the Saulsalito Kenny Pap Smear group ride and then crashes into 6 riders
in front of her while claiming she "couldn't stop in time."

That's not how I stop my bike if I need to dig deep into the pro suitcase of
courage.

In fact, I would say a good proportion of maximum braking effort comes not from
how hard or quick you pull on the brake levers, but how quickly, how low, and how
rearward you shift your weight.

Your equation treats one of the most important aspects of maximum braking (i.e.
the lowering and shifting of center of mass rearward) as being a constant instead
of a rather large variable. *That's the fundamental mistake of your equation.

You wrote the equation for how Liz Hatch stops her bike, and not for how the
monkey stops his bike.

QID.

Christ, man, you ought to be ashamed of yourself.
This is so lame the Union of Face-Ripping Chimps
Internationale is thinking of kicking you out because they've
finally figured out you're just a soft-fingered human.

Putting your head down is for sprinting into giant
Coke cans, not for maximum braking. Any extra
braking effect is purely psychological, like closing
your eyes as you're about to hit a bump. Throwing your
weight back actually momentarily pushes the bike
forward. For ****'s sake, even George Hincapie knows
that - it's how he won Gent-Wevelgem by a fractional
tire width, throwing the bike in the sprint.

Go play your tuba and ride over Cat 5 girls' necks
with your stopping technique.

Ben
My new stopping technique is unstoppable.

In article ,
Susan Walker wrote:

Anton Berlin wrote:
On Nov 3, 6:48 am, Susan Walker wrote:
Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.
Depends.

Sorry Susan but even if an old person craps in their Depends it still
falls at9.806 65 m /s^2 exactly

It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

(space removed because R. is cranky)

--
Michael Press

Michael Press wrote:
Susan Walker wrote:
It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

g0 is another name for g_n. It is meaningless.

On Nov 5, 2:01*am, Michael Press wrote:
In article ,
*Susan Walker wrote:

Anton Berlin wrote:
On Nov 3, 6:48 am, Susan Walker wrote:
Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.
Depends.

Sorry Susan but even if an old person craps in their Depends it still
falls at9.806 65 m /s^2 exactly

It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

(space removed because R. is cranky)

Thank you. Now I'm only half-cranky. Please remove the other
extraneous space as it removes meaning from your units and insults
graphic artists everywhere.

I wrote earlier:
"Somebody posted a link to an article on how gravity is
not uniform everywhere on Earth. Would you mind explaining to a low
blood sugar individual how gravity can be a constant if the
gravitational force varies from place to place?"

While you are repeating (why I am not sure) what the standard constant
is, would you explain why you seem to be taking umbrage at gravity
itself not being a constant? Susan's "depends" seems to have set you
off.

Do we need gravity to have five decimal point precision even if it
doesn't? Contact Google. They'd probably hook the not-so constant
constant up to Google Earth so you could have five decimal precision
anywhere you go.

R

On Nov 5, 9:12*am, Susan Walker wrote:
Michael Press wrote:
Susan Walker wrote:
It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

g0 is another name for g_n. It is meaningless.

Welcome, ladies and gentlemen, to the First Annual Gravitational
Constant Context Contest. It promises to be a wonderful FAGCCC this
year with our two contestants battling it out with their frequent
ejaculations.
"Exactly!"
"Meaningless!"
"Yo Mama!"
Ha ha ha! You've just got to love the fire and articulation our
contestants bring to the fray!
First up, the opening tentative moves of You've Got Pull, followed by
the rebuttal phase, Lens THIS!, and finishing up with Who's Your
Daddy, G?*

Next up - Mauling Michael.

R

* The Yankees, of course.

In article ,
Susan Walker wrote:

Michael Press wrote:
Susan Walker wrote:
It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

g0 is another name for g_n. It is meaningless.

On the contrary it has meaning.
It means 9.80665 m /s^2 exactly.

--
Michael Press

In article
,
RicodJour wrote:

On Nov 5, 2:01Â*am, Michael Press wrote:
In article ,
Â*Susan Walker wrote:

Anton Berlin wrote:
On Nov 3, 6:48 am, Susan Walker wrote:
Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.
Depends.

Sorry Susan but even if an old person craps in their Depends it still
falls at9.806 65 m /s^2 exactly

It depends. g0 is meaningless.

g_n = 9.80665 m /s^2 exactly.

(space removed because R. is cranky)

Thank you. Now I'm only half-cranky. Please remove the other
extraneous space as it removes meaning from your units and insults
graphic artists everywhere.

I wrote earlier:
"Somebody posted a link to an article on how gravity is
not uniform everywhere on Earth. Would you mind explaining to a low
blood sugar individual how gravity can be a constant if the
gravitational force varies from place to place?"

While you are repeating (why I am not sure) what the standard constant
is, would you explain why you seem to be taking umbrage at gravity
itself not being a constant? Susan's "depends" seems to have set you
off.

Do we need gravity to have five decimal point precision even if it
doesn't? Contact Google. They'd probably hook the not-so constant
constant up to Google Earth so you could have five decimal precision
anywhere you go.

g_n is defined to be 9.80665 m/s^2.

http://en.wikipedia.org/wiki/Standard_gravity

--
Michael Press

RicodJour wrote:

On Nov 4, 2:59*pm, MagillaGorilla wrote:
RicodJour wrote:
On Nov 4, 7:42*am, MagillaGorilla wrote:

Also, I would never do a maximum braking effort because you would run the risk
of going over the bars or locking your front/rear wheel up and sliding out. *I
would only do a max effort braking if I had to do it to avoid being seriously
injured - i.e. hitting a guardrail or cross-traffic.

I am truly impressed with the articulation you are able to derive with
your nether fundamental orifice, but you're still talking out yer
ass. *You argue that maximum braking would stop a cyclist faster than
a car (ignoring reaction time entirely, which makes your contention
totally without merit), then argue that maximum braking is dangerous
and just as likely to launch the cyclist.

Well done! *Remember to wipe next time.


Ummm, yes, we would "ignore reaction time entirely" since to not assume that would
be idiotic. *And two, I love how you and everyone else talks about a bike not being
able to stop faster than a "car," but not once...NOT ****ING ONCE....do you queers
even explain that stopping distances vary widely between all makes and models of
cars and that for some bizarre reason, this FACT does not seem to bother you since
you continue to refer to a generic "car" in your supposed "scientific" analysis
with a just-as-generic "bike."

You people don't even know what the **** you are debating because you never
established what model/make car or bike you are comparing, yet this does not stop
you from arguing vehemently that "a bike" can't stop faster than "a car."

The word "bike" not only means a $6,000 race bike but also means a $275 Walmart
Redneck Racer. *You can't just use the word "bike" when talking about performance
anymore than a car.

But since you all have been jerking yourselves off using these non-descript terms,
and I'm the only one who seems to notice these little poignant details, it means
you're all full of ****.

At least you're back to your dodge and weave bull**** comfort zone.

Single case in question, single car, two experienced guys on bikes,

Riddle me this Einstein - was Michael Rasmussen also "experienced?"




psychotic behind the wheel of the car, one road the psychotic thinks
he owns, one accident, two injuries, one guy going to jail.

If it was an "accident," why is someone going to jail?





You can plug in the numbers...excuse me, could...excuse me, should -
ah, who the **** am I kidding? Ben cleaned your cage for you on the
physics, Michael bitched slap you with vehicle code, and numerous
people pelted you with rotten fruit on your atrocious logic.



You evidently didn't see my response to Michael's little vehicle code post, did you?
Here check it out:

http://www.nntpnews.net/f4566/dr-tho...52/index5.html




On a good day you'd be the slow monkey, on the outside, looking
in...just like here. Anyway, you grow tiresome as you have nothing to
add. Sorry Zippy. Better luck next thread!

R

You should go to college and then come back here and post.

Magilla