Bike Stopping distances?

On Mon, 19 Sep 2005 21:34:24 GMT, Bob wrote:

Looking for a chart with bike stopping distances. Perhaps there's
something out there where they compared brake types, pads, tires,
etc - maybe even under wet and dry conditions?

Too many varibles would be present to represent this in any meaningful
way. Tire grip, rider weight, height and posture, and road surface
conditions and grade all have a bearing on stopping distance. Decent
brakes will allow almost any rider to brake hard enough to cause the
rear wheel to lift; overly hard braking can induce a face plant,
particularly for a tall rider with an erect posture. The bike's brake
system, in fact, is usually not the limiting factor in my experience;
the rider's height and posture has at least as much bearing on
stopping distance.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
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Where's the hatrack writes:

Looking for a chart with bike stopping distances. Perhaps there's
something out there where they compared brake types, pads, tires,
etc - maybe even under wet and dry conditions?

Too many varibles would be present to represent this in any
meaningful way. Tire grip, rider weight, height and posture, and
road surface conditions and grade all have a bearing on stopping
distance. Decent brakes will allow almost any rider to brake hard
enough to cause the rear wheel to lift; overly hard braking can
induce a face plant, particularly for a tall rider with an erect
posture. The bike's brake system, in fact, is usually not the
limiting factor in my experience; the rider's height and posture has
at least as much bearing on stopping distance.

"rider height and posture has at least as much bearing on stopping
distance." and tires or road surface is a dodge. For any given test
rider a comparative chart could be made holding those parameters
constant. The main feature of a brake is the ease with which a rider
can control speed for cornering and stopping, and that is harder to
assess without some subjective evaluation by the tester. Stopping
distance is not the main concern with bicycle brakes because with a
capable rider, most brakes can raise the rear wheel in a straight line
stop given a strong hand on the lever.

As a great example, the Campagnolo Delta brake had good stopping power
but was ultimately scrapped because it had poor modulation, having a
non-linear mechanical advantage that increased steeply as pads wore.

Jobst Brandt

On Tue, 20 Sep 2005 15:50:49 GMT,
wrote:

Where's the hatrack writes:

Looking for a chart with bike stopping distances. Perhaps there's
something out there where they compared brake types, pads, tires,
etc - maybe even under wet and dry conditions?

Too many varibles would be present to represent this in any
meaningful way. Tire grip, rider weight, height and posture, and
road surface conditions and grade all have a bearing on stopping
distance. Decent brakes will allow almost any rider to brake hard
enough to cause the rear wheel to lift; overly hard braking can
induce a face plant, particularly for a tall rider with an erect
posture. The bike's brake system, in fact, is usually not the
limiting factor in my experience; the rider's height and posture has
at least as much bearing on stopping distance.

..."rider height and posture has at least as much bearing on stopping
distance." and tires or road surface is a dodge. [snip] Stopping
distance is not the main concern with bicycle brakes because with a
capable rider, most brakes can raise the rear wheel in a straight line
stop given a strong hand on the lever.

True, but...

The question was about the actual stopping distances that would be
obtained, and my point is that this is a flexible number with
mechanical, local and biological components which make test numbers
less than useful as a predictor of real-world results. The bike's
capabilities can, as you correctly state, be safely assumed to be in
excess of what is required to produce the minimum stopping distance
for given conditions, but the rider's actions and abilities are an
unknown which is hard to quantify.

As a starting point, in my direct experience, not all riders (myself
included) are given to habitually using a either a constant posture or
one that keeps the center of mass as low as practical, and one does
not always have the option of changing posture to get the center of
mass down during an emergency stop. If the center of mass is high,
the available braking effort without spilling will be lower than if
the cm was better located relative to the contact patch. I have
encountered a number of oh-sh*t situations in which I ended up either
stopping longer than I preferred or going down because I couldn't get
low fast enough while applying the brakes. (Fortunately for me, I
don't ride so aggressively that these resulted in major
calamities...but a less cautious rider might have had different
results.)

Add to this the fact that many bikes come with brakes that require
relatively little hand effort to lock the front wheel, and the issue
becomes even less predictable; in an emergency, a common reaction is
to grab for the brakes overly hard; this is more likely to result in a
spill than to produce a minimum-distance controlled stop in my
opinion.

My point, therefore, is that in the scope of common on-street riding,
the limiting factor in a given situation will more often be the
rider's habits and the local conditions rather than the braking
ability of the bike. The brakes will, as you say, almost always have
more capability than can be used...but if the center of mass is at too
great an angle to the front contact patch, or if the rider is
underskilled in the use of the brakes, the deceleration capability for
the system as a whole may be below what is needed at the moment though
the available stopping distance may have been adequate if the rider
was tucked and practised. (This assumes that gravel, leaves, oily
surfaces and the like are not present as compliications.)

Although this might seem like a strong argument in favor of developing
better riding posture and skills, a demonstration of the fact that
such advice will not always either be heeded or prove useful was
provided this morning. On the way to dropping my daughter off at
school, I saw a rider take a dive about a block in front of me when he
applied the brakes hard to avoid a car that had backed out in front of
him across the bike lane. He was not particularly erect on the saddle,
but his center of mass was artificially high due to the presence of a
backpack full of books. When he went for the brakes at what I would
guess was about 12 to 14 mph, he applied them a bit too hard for the
conditions, lifted the rear wheel a bit much, and went down at an
angle. Luckily for him, he was essentially uninjured. The driver of
the vehicle may not have even realized that he'd caused the rider to
spill; he drove off without looking back. The rider and bike landed
about ten feet short of the driveway that the car emerged from. The
street has some trees along it, but the car's driver should have been
able to see the bike approaching. I'm guessing that he glanced once,
and then backed out without checking again.

Brake system capabilities aren't the issue, IMO. It's the rider and
the conditions that will determine the stopping distance...and that
distance may not be short enough to avoid a collision even when it's
as short as could be reasonably achieved.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Where's the hatrack writes:

Although this might seem like a strong argument in favor of
developing better riding posture and skills, a demonstration of the
fact that such advice will not always either be heeded or prove
useful was provided this morning. On the way to dropping my
daughter off at school, I saw a rider take a dive about a block in
front of me when he applied the brakes hard to avoid a car that had
backed out in front of him across the bike lane. He was not
particularly erect on the saddle, but his center of mass was
artificially high due to the presence of a backpack full of books.

When he went for the brakes at what I would guess was about 12 to 14
mph, he applied them a bit too hard for the conditions, lifted the
rear wheel a bit much, and went down at an angle. Luckily for him,
he was essentially uninjured. The driver of the vehicle may not
have even realized that he'd caused the rider to spill; he drove off
without looking back. The rider and bike landed about ten feet
short of the driveway that the car emerged from. The street has
some trees along it, but the car's driver should have been able to
see the bike approaching. I'm guessing that he glanced once, and
then backed out without checking again.

I doubt that the sequence of events went as you surmise. He most
likely "went over the bars" for the same reason most (aka overwhelming
majority) such incidents occur; that being that the bicycle overturned
when his legs hit the handlebars. This is the cause of nearly all
such endos. Riders who do this generally cannot, in normal posture
(bracing arms), raise the rear wheel by braking if they were to try.

http://www.sheldonbrown.com/brandt/over-the-bars.html

Brake system capabilities aren't the issue, IMO. It's the rider and
the conditions that will determine the stopping distance...and that
distance may not be short enough to avoid a collision even when it's
as short as could be reasonably achieved.

I, for one, do not like the effect of water on the rim, be that with
rain, or worse, with snow on the rim inner circumference. The snow
effect is worse, because with snow, braking does not come back until
all the snow is melted. It makes clear that even in rain, rim brakes
only work where there is partial dryness, other wise it's like a razor
gliding effortlessly over the skin. Because there is so little
braking on a wet rim, the snow is not readily melted so it takes far
longer than one expects. It's times like these when disc brakes start
looking like a solution. Fortunately, this doesn't occur often enough
to warrant the change.

Jobst Brandt

wrote in message
...
Where's the hatrack writes:

Although this might seem like a strong argument in favor of
developing better riding posture and skills, a demonstration
of the
fact that such advice will not always either be heeded or
prove
useful was provided this morning. On the way to dropping my
daughter off at school, I saw a rider take a dive about a
block in
front of me when he applied the brakes hard to avoid a car
that had
backed out in front of him across the bike lane. He was not
particularly erect on the saddle, but his center of mass was
artificially high due to the presence of a backpack full of
books.

When he went for the brakes at what I would guess was about
12 to 14
mph, he applied them a bit too hard for the conditions,
lifted the
rear wheel a bit much, and went down at an angle. Luckily
for him,
he was essentially uninjured. The driver of the vehicle may
not
have even realized that he'd caused the rider to spill; he
drove off
without looking back. The rider and bike landed about ten
feet
short of the driveway that the car emerged from. The street
has
some trees along it, but the car's driver should have been
able to
see the bike approaching. I'm guessing that he glanced once,
and
then backed out without checking again.

I doubt that the sequence of events went as you surmise. He
most
likely "went over the bars" for the same reason most (aka
overwhelming
majority) such incidents occur; that being that the bicycle
overturned
when his legs hit the handlebars. This is the cause of nearly
all
such endos. Riders who do this generally cannot, in normal
posture
(bracing arms), raise the rear wheel by braking if they were to
try.

http://www.sheldonbrown.com/brandt/over-the-bars.html

Brake system capabilities aren't the issue, IMO. It's the
rider and
the conditions that will determine the stopping
distance...and that
distance may not be short enough to avoid a collision even
when it's
as short as could be reasonably achieved.

I, for one, do not like the effect of water on the rim, be that
with
rain, or worse, with snow on the rim inner circumference. The
snow
effect is worse, because with snow, braking does not come back
until
all the snow is melted. It makes clear that even in rain, rim
brakes
only work where there is partial dryness, other wise it's like
a razor
gliding effortlessly over the skin. Because there is so little
braking on a wet rim, the snow is not readily melted so it
takes far
longer than one expects. It's times like these when disc
brakes start
looking like a solution. Fortunately, this doesn't occur often
enough
to warrant the change.

I have literally been unable to stop (without dragging a foot)
while descending in the rain with some mid-90s cantilevers
coupled with STI levers. The mechanical advantage mis-match was
a real problem that took a lot of fiddling to remedy. The Salmon
KoolStops make most competent single and dual pivot brakes
passable in the rain.

For me, braking in the rain takes a distant back seat to
traction. I crashed twice a couple weeks ago while riding in the
rain, the second time on a steep descent. I managed to break a
couple ribs (let me tell you, that hurts like hell). My front
wheel washed out -- an Avocet 25mm Carbon 12 tire that I had
retired from another bike because I thought it was slippery. I
wonder if Avocet has changed its compound. They just do not seem
to stick as well as they used to. -- Jay Beattie.

Sorry about your crash, but if you thought the tire was too slippery way did
you then ride it in the rain? I also wonder if the Avocet compound has been
changed now. Maybe they followed other companies and added silica to the
rubber. Silica reputed to be bad in the rain.

cel

"Jay Beattie" wrote in message
...

wrote in message
...
Where's the hatrack writes:

Although this might seem like a strong argument in favor of
developing better riding posture and skills, a demonstration
of the
fact that such advice will not always either be heeded or
prove
useful was provided this morning. On the way to dropping my
daughter off at school, I saw a rider take a dive about a
block in
front of me when he applied the brakes hard to avoid a car
that had
backed out in front of him across the bike lane. He was not
particularly erect on the saddle, but his center of mass was
artificially high due to the presence of a backpack full of
books.

When he went for the brakes at what I would guess was about
12 to 14
mph, he applied them a bit too hard for the conditions,
lifted the
rear wheel a bit much, and went down at an angle. Luckily
for him,
he was essentially uninjured. The driver of the vehicle may
not
have even realized that he'd caused the rider to spill; he
drove off
without looking back. The rider and bike landed about ten
feet
short of the driveway that the car emerged from. The street
has
some trees along it, but the car's driver should have been
able to
see the bike approaching. I'm guessing that he glanced once,
and
then backed out without checking again.

I doubt that the sequence of events went as you surmise. He
most
likely "went over the bars" for the same reason most (aka
overwhelming
majority) such incidents occur; that being that the bicycle
overturned
when his legs hit the handlebars. This is the cause of nearly
all
such endos. Riders who do this generally cannot, in normal
posture
(bracing arms), raise the rear wheel by braking if they were to
try.

http://www.sheldonbrown.com/brandt/over-the-bars.html

Brake system capabilities aren't the issue, IMO. It's the
rider and
the conditions that will determine the stopping
distance...and that
distance may not be short enough to avoid a collision even
when it's
as short as could be reasonably achieved.

I, for one, do not like the effect of water on the rim, be that
with
rain, or worse, with snow on the rim inner circumference. The
snow
effect is worse, because with snow, braking does not come back
until
all the snow is melted. It makes clear that even in rain, rim
brakes
only work where there is partial dryness, other wise it's like
a razor
gliding effortlessly over the skin. Because there is so little
braking on a wet rim, the snow is not readily melted so it
takes far
longer than one expects. It's times like these when disc
brakes start
looking like a solution. Fortunately, this doesn't occur often
enough
to warrant the change.

I have literally been unable to stop (without dragging a foot)
while descending in the rain with some mid-90s cantilevers
coupled with STI levers. The mechanical advantage mis-match was
a real problem that took a lot of fiddling to remedy. The Salmon
KoolStops make most competent single and dual pivot brakes
passable in the rain.

For me, braking in the rain takes a distant back seat to
traction. I crashed twice a couple weeks ago while riding in the
rain, the second time on a steep descent. I managed to break a
couple ribs (let me tell you, that hurts like hell). My front
wheel washed out -- an Avocet 25mm Carbon 12 tire that I had
retired from another bike because I thought it was slippery. I
wonder if Avocet has changed its compound. They just do not seem
to stick as well as they used to. -- Jay Beattie.

wrote:
Sorry about your crash, but if you thought the tire was too slippery way did
you then ride it in the rain? I also wonder if the Avocet compound has been
changed now. Maybe they followed other companies and added silica to the
rubber. Silica reputed to be bad in the rain.

there's no reason for silica compunds to be bad in the rain. michelins
certainly aren't, but they use a dual compound solution to make sure.
carbon compounds can be tuned for rolling resistance /or/ grip, not
both. silica /can/ be tuned for both, hence its increasing use in both
bike & automotive apps.


cel

"Jay Beattie" wrote in message
...

wrote in message
...

Where's the hatrack writes:


Although this might seem like a strong argument in favor of
developing better riding posture and skills, a demonstration

of the

fact that such advice will not always either be heeded or

prove

useful was provided this morning. On the way to dropping my
daughter off at school, I saw a rider take a dive about a

block in

front of me when he applied the brakes hard to avoid a car

that had

backed out in front of him across the bike lane. He was not
particularly erect on the saddle, but his center of mass was
artificially high due to the presence of a backpack full of

books.

When he went for the brakes at what I would guess was about

12 to 14

mph, he applied them a bit too hard for the conditions,

lifted the

rear wheel a bit much, and went down at an angle. Luckily

for him,

he was essentially uninjured. The driver of the vehicle may

not

have even realized that he'd caused the rider to spill; he

drove off

without looking back. The rider and bike landed about ten

feet

short of the driveway that the car emerged from. The street

has

some trees along it, but the car's driver should have been

able to

see the bike approaching. I'm guessing that he glanced once,

and

then backed out without checking again.

I doubt that the sequence of events went as you surmise. He

most

likely "went over the bars" for the same reason most (aka

overwhelming

majority) such incidents occur; that being that the bicycle

overturned

when his legs hit the handlebars. This is the cause of nearly

all

such endos. Riders who do this generally cannot, in normal

posture

(bracing arms), raise the rear wheel by braking if they were to

try.

http://www.sheldonbrown.com/brandt/over-the-bars.html


Brake system capabilities aren't the issue, IMO. It's the

rider and

the conditions that will determine the stopping

distance...and that

distance may not be short enough to avoid a collision even

when it's

as short as could be reasonably achieved.

I, for one, do not like the effect of water on the rim, be that

with

rain, or worse, with snow on the rim inner circumference. The

snow

effect is worse, because with snow, braking does not come back

until

all the snow is melted. It makes clear that even in rain, rim

brakes

only work where there is partial dryness, other wise it's like

a razor

gliding effortlessly over the skin. Because there is so little
braking on a wet rim, the snow is not readily melted so it

takes far

longer than one expects. It's times like these when disc

brakes start

looking like a solution. Fortunately, this doesn't occur often

enough

to warrant the change.

I have literally been unable to stop (without dragging a foot)
while descending in the rain with some mid-90s cantilevers
coupled with STI levers. The mechanical advantage mis-match was
a real problem that took a lot of fiddling to remedy. The Salmon
KoolStops make most competent single and dual pivot brakes
passable in the rain.

For me, braking in the rain takes a distant back seat to
traction. I crashed twice a couple weeks ago while riding in the
rain, the second time on a steep descent. I managed to break a
couple ribs (let me tell you, that hurts like hell). My front
wheel washed out -- an Avocet 25mm Carbon 12 tire that I had
retired from another bike because I thought it was slippery. I
wonder if Avocet has changed its compound. They just do not seem
to stick as well as they used to. -- Jay Beattie.

"jim beam" wrote in message
...
wrote:
Sorry about your crash, but if you thought the tire was too
slippery way did
you then ride it in the rain? I also wonder if the Avocet
compound has been
changed now. Maybe they followed other companies and added
silica to the
rubber. Silica reputed to be bad in the rain.

there's no reason for silica compunds to be bad in the rain.
michelins
certainly aren't, but they use a dual compound solution to make
sure.
carbon compounds can be tuned for rolling resistance /or/ grip,
not
both. silica /can/ be tuned for both, hence its increasing use
in both
bike & automotive apps.


Honestly, I had forgotten why I shifted that tire from one bike
to the other -- until after the crash. And it was not that bad
of a tire -- it just was not as good as the tires on my regular
rain bike, which was out of commission due to a broken brake
bridge.

I doubt Avocet has started adding silica, being that the tire is
named the Carbon 12 -- although they may have changed other
constituents of the compound which may affect traction, like
percentages of natural and synthetic rubber, resins, etc.
Carbon based compounds do tend to give better traction in the
rain, IMO, but there are some excellent soft compound silica
based tires out there that do just as well or better. Finally,
to be fair, I have no way of knowing whether this fall was some
weird fluke or whether it was due to preventable slip-out. My
real point is that slip out and traction are, for me, much more
real concerns than slightly reduced braking in the rain. Indeed,
my regular rain bike has nearly 30 year old single pivot Campy NR
brakes, and they worked fine. -- Jay Beattie.

On Wed, 21 Sep 2005 17:20:34 GMT,
wrote:

I doubt that the sequence of events went as you surmise. He most
likely "went over the bars" for the same reason most (aka overwhelming
majority) such incidents occur; that being that the bicycle overturned
when his legs hit the handlebars. This is the cause of nearly all
such endos. Riders who do this generally cannot, in normal posture
(bracing arms), raise the rear wheel by braking if they were to try.

That may be the case; I was a block behind, so it was difficult to
make out details even though the view was unobstructed. (I stopped to
make sure he was OK, though; he was mostly just annoyed at his nearly
scraped-through right glove than anything else.)

The important factor in my estimation remains that the rider is more
of a limiting factor than the bike when it comes to stopping distance.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

ooddlee timed
prime meat for disc brakes
'ceptin the need isn't constant, the irritation and rash insuffiecnt to
propell yawl to the nbar catalog's disc brake page and OCR
lovely rita pete off course.