Bicycle Stopping Distances

In article ,
"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.

You can try this. Start braking with only the rear brake,
moderate to heavy braking, but short of skidding the rear
tire. Now apply the front brake heavily. You will skid the
rear tire.

--
Michael Press

Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.

Depends.

Ryan Cousineau wrote:

In article
,
Anton Berlin wrote:

In a head to head test and in normal conditions a bike should be able
to stop faster than a car.

But that includes that the rider has both hands on the bars (and
brakes) which is hard to do when you're flipping someone off.

At 50 kmh

http://www.exploratorium.edu/cycling/brakes2.html

Bike stops in 10 meters

http://www.forensicdynamics.com/stopdistcalc

Car stops in 14 meters.

I hate proving Kunich wrong (again) at the expense of proving Magilla
right.

But Kunich may be right on an empirical basis. It make take several
hundred meters to slow his fat ass to a stop.

Besides this is all theory as we know Kunich has never gone 30 mph on
a bike.

The missing factor is essentially reaction time, which probably explains
how Dr. Evil managed to whomp two riders with his trunk.

The 2 jackass cyclists never slowed down to less than 30 mph when they hit
the Infiniti. That's not even close to stopping. That's what happens when
you're too busy flipping off a driver instead of maintaining control of
your bicycle as required under the California traffic code.

Magilla

Tom Kunich wrote:

"Ryan Cousineau" wrote in message
]...
In article
,
Anton Berlin wrote:

In a head to head test and in normal conditions a bike should be able
to stop faster than a car.

But that includes that the rider has both hands on the bars (and
brakes) which is hard to do when you're flipping someone off.

At 50 kmh

http://www.exploratorium.edu/cycling/brakes2.html

Bike stops in 10 meters

http://www.forensicdynamics.com/stopdistcalc

Car stops in 14 meters.

I hate proving Kunich wrong (again) at the expense of proving Magilla
right.

But Kunich may be right on an empirical basis. It make take several
hundred meters to slow his fat ass to a stop.

Besides this is all theory as we know Kunich has never gone 30 mph on
a bike.

The missing factor is essentially reaction time, which probably explains
how Dr. Evil managed to whomp two riders with his trunk.

Here's a claim that reaction times vary around 0.7-1.5 s for drivers in
braking situations.

That suggests that if the Doctor swerved and braked fast enough, the
riders would not have had time to react before hitting the car. He's
effectively got about a 1-second head start on braking, and at 50 km/h,
that's about 14 meters.

In other words, the car could be at zero km/h before the riders got to
their brakes, and the rest depends on how closely in front of them he
cut.

Considering he seems to have been trying to injure them, I'm going to
guess really close, like 5m.

I figure that scenario as being 14 metres of stopping distance but about
24 metres of rt+ideal stopping. In other words, physics says those
cyclists were gonna hit the car no matter how good their brakes, as long
as their reaction times were within human norms.

Gerbils or monkeys may have better reaction times than humans, though.

As usual, those who fail to think do the most talking.

The brakes on a modern car will stop the car at a rate of about one gee.
Race cars commonly brake well above one gee. Moreover, car tires, which
cover a large portion of the road and put more square inches of rubber on
the road per lb. of load, are less susceptible to road conditions, gravel
etc. on the road and other traction problems.

Because of the high center of gravity a bicycle has, the braking force you
can apply while sitting normally on the saddle is about 1/2 gee. Got that?
HALF the braking force of a car. You can increase your braking force to
perhaps .85 gees by sliding backwards and putting your stomach on the
saddle. This unfortunately greatly decreases your control of the bicycle
while increasing your ability to brake by lowering your center of gravity.
Note that normally the time to slide back like that would take more
time/distance than the slightly improved braking would justify.

The reaction time for both the driver and the rider are the same and so can
be ignored when discussing stopping distances at equal speeds.

So you would rather have a car run over your hand than a bicycle with a 150
pound rider on it? According to you, you would, because a car has "more
square inches of rubber on the road per lb."

I'll be more than happy to be the car driver in that experiment. Let's meet
at the Saulsalito cafe, tomorrow afternoon. Bring your health insurance ID
card.

Magilla

Tom Kunich wrote:

"DirtRoadie" wrote in message
...
On Nov 1, 5:50 pm, "Tom Kunich" wrote:

The reaction time for both the driver and the rider are the same and so
can
be ignored when discussing stopping distances at equal speeds.

Huh? How can the driver's "reaction time" be relevant what he has
nothing to react to?

I'm speaking purely of stopping ability as on a test course.

In the case of the relevant assault, since it takes between .7 and 1.5
seconds or so to react, and if the driver cut in close enough there wouldn't
be sufficient time to react and hence no way whatsoever to avoid running
into the back of the car.

So you're telling me a 3,500 lb. car can completely move over in front of 2
cyclists and that the cyclists would have "no time" to react. I hate to tell
you, Tom, but to move a vehicle from not being front of 2 cyclists to being
completely in front of the cyclists takes TIME. There was plenty of time for
the cyclists to react. Yet according to the GPS, they couldn't even slow down
to less than 30 mph, which means they likely never even grabbed a brake lever.

Probably because they were flipping off the driver. Now Ron "Kiefel" Peterson
has a Michael Jackson nose.

Magilla

Michael Press wrote:
and the value is 9.806 65 m /s^2 exactly.

Susan Walker wrote:
Depends.

http://news.bbc.co.uk/2/hi/science/nature/1668872.stm

DirtRoadie wrote:

On Nov 1, 5:50*pm, Anton Berlin wrote:

However as we all know it's more prudent to run over cyclists from
behind if you want to avoid the legal tangles.

In fact it might be one of the easiest ways on the planet to kill
someone without consequences.

I respectfully disagree. My impression, based upon an experience I
had, is that it would be easy for the driver of a motorized vehicle to
do insure damage by pulling closely in front of a paceline or similar
group of cyclists, hitting the brakes and causing the front riders to
also hit their brakes. This causes the following riders to plow into
the leading riders and if done properly, causes them all to crash in a
nice pileup. If executed by a skilled perpetrator there need not be
any contact between the car and riders and the driver can depart with
no physical evidence of any involvement. After all, a broken rear
window and/or blood is far too messy.

In the LA road rage trial, relative braking distances and/or
capabilities of bikes vs. cars is a red herring thrown in by sleazy
defense counsel trying to divert the jury's attention from the fact
that the dear doctor performed a deliberate and illegal act which
caused exactly the illegal results which might have been expected.

DR

So riddle me this, jackass...how come this cop wasn't charged with even
careless driving?

http://www.kold.com/global/story.asp?s=7959848

Thanks,

Magilla

DirtRoadie wrote:

On Nov 1, 5:50*pm, Anton Berlin wrote:

However as we all know it's more prudent to run over cyclists from
behind if you want to avoid the legal tangles.

In fact it might be one of the easiest ways on the planet to kill
someone without consequences.

I respectfully disagree. My impression, based upon an experience I
had, is that it would be easy for the driver of a motorized vehicle to
do insure damage by pulling closely in front of a paceline or similar
group of cyclists, hitting the brakes and causing the front riders to
also hit their brakes. This causes the following riders to plow into
the leading riders and if done properly, causes them all to crash in a
nice pileup.

Most cyclists in group rides are spazzes and are well capable of crashing
thesmelves without anyone doing anything. Haven't you ever watched the
Tour de France? Half those Euro guys have no idea what the **** they are
doing. Some of the most ****ed up riders I've ever seen are in the pro
ranks.


If executed by a skilled perpetrator there need not be
any contact between the car and riders and the driver can depart with
no physical evidence of any involvement. After all, a broken rear
window and/or blood is far too messy.


In the LA road rage trial, relative braking distances and/or
capabilities of bikes vs. cars is a red herring thrown in by sleazy
defense counsel trying to divert the jury's attention from the fact
that the dear doctor performed a deliberate and illegal act which
caused exactly the illegal results which might have been expected.

DR

You mean the OJ Simpson jury or the Robert Blake jury?

Magilla

"Paul B. Anders" wrote:

On Nov 1, 10:09*am, Anton Berlin wrote:
In a head to head test and in normal conditions a bike should be able
to stop faster than a car.

But that includes that the rider has both hands on the bars (and
brakes) which is hard to do when you're flipping someone off.

At 50 kmh

http://www.exploratorium.edu/cycling/brakes2.html

Bike stops in 10 meters

http://www.forensicdynamics.com/stopdistcalc

Car stops in 14 meters.

I hate proving Kunich wrong (again) at the expense of proving Magilla
right.

But Kunich may be right on an empirical basis. *It make take several
hundred meters to slow his fat ass to a stop.

Besides this is all theory as we know Kunich has never gone 30 mph on
a bike.

Plug in 50 mph. Anyone who has done any high-speed descending who
believes a bike can stop from 50 mph in under 100 feet is smoking
weed. It's laughable. Go descend Carson or Monitor passes in the
Sierra's, where you can hit 50 mph easily, and do a full-on panic stop
and see if you can do this.

Brad

Yes, I believe I can stop a bike from 50 mph in about 94 feet. You're
talking about maximum braking effort here, not some avg. effort. It
technically wouldn't even be safe to conduct such a braking experiment
because bikes don't have ABS and you would almost have to lock the wheels
up in order to see where the limit would be.

So I would not expect anyone to stop at that distance in any little Johnny
Carson Valley Rd. test. This is a maximum braking effort where it would
be dangerous to actually do. And anyone who would do it on their road bike
is probably too ****ing stupid to do it correctly.

But the test does not assume you would be doing it on a descent either.


Thanks,


Magilla

" wrote:

On Nov 2, 10:44*am, "Paul B. Anders" wrote:
On Nov 1, 10:09*am, Anton Berlin wrote:



In a head to head test and in normal conditions a bike should be able
to stop faster than a car.

But that includes that the rider has both hands on the bars (and
brakes) which is hard to do when you're flipping someone off.

At 50 kmh

http://www.exploratorium.edu/cycling/brakes2.html

Bike stops in 10 meters

http://www.forensicdynamics.com/stopdistcalc

Car stops in 14 meters.

I hate proving Kunich wrong (again) at the expense of proving Magilla
right.

But Kunich may be right on an empirical basis. *It make take several
hundred meters to slow his fat ass to a stop.

Besides this is all theory as we know Kunich has never gone 30 mph on
a bike.

Plug in 50 mph. Anyone who has done any high-speed descending who
believes a bike can stop from 50 mph in under 100 feet is smoking
weed. It's laughable. Go descend Carson or Monitor passes in the
Sierra's, where you can hit 50 mph easily, and do a full-on panic stop
and see if you can do this.

Brad

Listen up monkeys,

The calculator is wrong because they did not
consider that a bike's braking ability is limited
by going over the bars.

The calculator, for 30 mph = 13.4 m/s, returns
a stopping distance of 10.4 meters. This
translates to a deceleration of 8.6 m/s^2, from
distance = 0.5 * (initial velocity)^2/ acceleration.

This is suspiciously close to 1 g = 9.8 m/s^2
times the "adhesion coefficient" of 0.85 that the
calculator suggests. So I think they assumed
that a bike can brake at slightly less than 1 g,
slightly less because it's limited by tire adhesion.

However, everyone who thinks about this says that
a bike can't do that because of the high center of mass.

On what basis do you come to the definitive conclusion that "everyone" who
"thinks about this" says that a bike "can't do" 0.85 g's?

Who the **** knows what 0.85g is on their bike? Are you a douchebag or
something? Plus, the fact that you use positive G's to indicate
deceleration when only negative G's would apply gives me tremendous
consternation that you're a jackass.

You people better start cleaning up your act in here or I'm gonna go
chimp-face on you.




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.

"Most people agree"...WRONG. most people have no ****ing clue what .6 vs.
1.3 G's on a bike is. I just love how you claim that people know the
difference between G forces measured in the hundredths of a G! You've got
to be kidding me with this bull**** sales pitch, Jimmy Mays.




If you use 0.6 g to calculate the stopping distance
from 30 mph, it's 15.2 meters. And that is assuming
absolutely perfect conditions and flat ground,
not down hill, which makes the endo problem worse.

So no, a bike cannot stop faster than a car.

Ben

Yeah, like you really proved it with statements like "most people agree" and
declaing what the maximum deceleration is on a bike without showing how you
came up with those numbers.

Nice ****ing "data." (your own declarations that show no work)


Magilla