Braking distance for bicycles with all relevant data explained

MrCheerful wrote:
On 22/02/2016 10:42, John Smith wrote:
MrCheerful wrote:

Then why can't they stop at traffic lights? or pedestrian crossings, Or
before riding into the side of a bus? back of a car, pedestrian, other
cyclist, toddler, lamp post , dog etc. etc.

Please contract pancreatic cancer.


What a witty response, you must be so proud of your intellectual put downs.

Why should I - or anyone else for that matter - bother with 'intellectual
putdowns' when faced with a cretinous ****hair like you?

--
john smith |MA (Hons)|MPhil (Hons)|CAPES (mention très bien)|LLB (Hons)
'It never gets any easier. You just get faster'
(Greg LeMond (1961 - ))

MrCheerful wrote:
On 21/02/2016 21:20, Paul George wrote:
On Sunday, February 21, 2016 at 7:06:35 PM UTC, Peter Parry wrote:

Interesting - there isn't much published research on the subject.

Perhaps because there are too many variables involved.

Hophead fixie peddlars always claim they can stop instantly (perhaps in
their heads they are)

It must be so stressful to be a hater.

but it is interesting to see that for most push bikes they can't even
come close to the outdated 12m overall stopping distance (6m braking
distance) for a car at 20MPH.

But they can.

Then why can't they stop at traffic lights? or pedestrian crossings, Or
before riding into the side of a bus? back of a car, pedestrian, other
cyclist, toddler, lamp post , dog etc. etc.

'Police installed first traffic camera at a sign south of Paris, and
are now chasing 517 drivers who ignored it in just one day...'
http://www.theguardian.com/world/2016/feb/22/stop-a-four-letter-word-for-french-drivers-traffic-camera-shows

I should be very surprised if the figures were not higher in Psycholand.

--
john smith |MA (Hons)|MPhil (Hons)|CAPES (mention très bien)|LLB (Hons)
'It never gets any easier. You just get faster'
(Greg LeMond (1961 - ))

On Mon, 22 Feb 2016 00:10:35 -0000, "TMS320" wrote:

"Paul George" wrote
On Sunday, February 21, 2016 at 7:06:35 PM UTC, Peter Parry wrote:

but it is interesting to see that for most
push bikes they can't even come close to the outdated 12m overall
stopping distance (6m braking distance) for a car at 20MPH.

It's not a like for like comparision. Driver reaction adds another 6m. There
also needs to be an addition of 2m for distance of the front of the car
ahead of the driver's eyes.

If we simply consider braking distance and assume that the reaction
time will not be dramatically different between cyclists and motorists
then with a car the limiting factor is the rate of deceleration which
can be achieved. All the figures below are for braking distances
only.

On a dry tarmac road driver skill is relatively unimportant as long as
they brake hard. With a car deceleration at max braking is set by the
adhesion of the tyres to the road surface and with modern cars and
tyres on a tarmac surface is about 0.9g. A moderately degraded road
surface will not significantly affect braking. However, in an
emergency most drivers will not brake to the cars maximum capability
(hence the introduction of Emergency Brake Assist).

With a push bike rider skill is a far more important factor than with
a car Most riders are unable to achieve anything like the best the
cycle can brake at. The quality of the road surface also has a major
impact. The average rider rarely manages more than 0.35g.

However, if we assume the surface is dry and pristine and the
pushbike is braking at the best the machine can achieve the limit for
the pushbike is not the adhesion of the tyre on the road but weight
transfer which can cause pitch over at about 0.6g (the subsequent
adhesion of shredded flesh to tarmac is not usually considered to be
part of stopping distance).

It would appear that the calculator you used at exploratorium.edu is
significantly wrong. For a speed of 24.85 MPH it gives a stopping
distance of 7.14m. A test of the Shimano R785 Hydraulic road disc
brakes at that speed for review produced stopping distances of 14m.
The Campagnolo Chorus calipers and alloy rims produced similar
results. At 15MPH a Dutch bicycle (new) fitted with disk brakes
could stop in 5m, the web calculator claimed 2.6m.

The latest Highway code braking distances have been reduced somewhat
and appear to assume retardation of about 0.65g.This produces a
braking distance figure from 60MPH of 54m, a test by Which? on some
fairly average cars produced stopping distances at that speed between
34 and 44m.

Time to brake to stop is the speed in metres per second divided by the
deceleration rate. Cars can always decelerate more rapidly than
bicycles. There doesn't appear to be any doubt that a car can stop
more quickly than any bike at comparable speeds. In the rain the
disparity increases considerably.

On Monday, February 22, 2016 at 8:37:24 AM UTC, MrCheerful wrote:
On 21/02/2016 23:45, Paul George wrote:
On Sunday, February 21, 2016 at 11:40:21 PM UTC, MrCheerful wrote:

I made no such claim, but in the absence of better qualified data I take
the word of experts.

What better data do you want than a real world video?



Is there evidence of speed and distance ?

It was Argyle St Birkenhead, near Birkenhead Central station.
You can to to google maps and measure speed and distance for yourself.

"Peter Parry" wrote
On Mon, 22 Feb 2016 00:10:35 -0000, "TMS320" wrote:
"Paul George" wrote
On Sunday, February 21, 2016 at 7:06:35 PM UTC, Peter Parry wrote:

but it is interesting to see that for most
push bikes they can't even come close to the outdated 12m overall
stopping distance (6m braking distance) for a car at 20MPH.

It's not a like for like comparision. Driver reaction adds another 6m.
There
also needs to be an addition of 2m for distance of the front of the car
ahead of the driver's eyes.

If we simply consider braking distance and assume that the reaction
time will not be dramatically different between cyclists and motorists
then with a car the limiting factor is the rate of deceleration which
can be achieved. All the figures below are for braking distances
only.

On a dry tarmac road driver skill is relatively unimportant as long as
they brake hard. With a car deceleration at max braking is set by the
adhesion of the tyres to the road surface and with modern cars and
tyres on a tarmac surface is about 0.9g. A moderately degraded road
surface will not significantly affect braking. However, in an
emergency most drivers will not brake to the cars maximum capability
(hence the introduction of Emergency Brake Assist).

With a push bike rider skill is a far more important factor than with
a car Most riders are unable to achieve anything like the best the
cycle can brake at. The quality of the road surface also has a major
impact. The average rider rarely manages more than 0.35g.

Do you mean that an average rider rarely does more than 0.35g by routine? Or
has this figure been determined by putting a sample through controlled
stress
tests? Many countries allow bikes with rear brake only - are you sure you're
not confusing two different things?

If it is 'by routine' then drivers rarely do more than 0.35g.

However, if we assume the surface is dry and pristine and the
pushbike is braking at the best the machine can achieve the limit for
the pushbike is not the adhesion of the tyre on the road but weight
transfer which can cause pitch over at about 0.6g (the subsequent
adhesion of shredded flesh to tarmac is not usually considered to be
part of stopping distance).

Pitchover is higher than 0.6g. Although there are techniques of improving
weight distribution to stop pitchover during deep braking, I expect most
cases are low speed when the rider puts feet down too soon.

It would appear that the calculator you used at exploratorium.edu is
significantly wrong. For a speed of 24.85 MPH it gives a stopping
distance of 7.14m. A test of the Shimano R785 Hydraulic road disc
brakes at that speed for review produced stopping distances of 14m.
The Campagnolo Chorus calipers and alloy rims produced similar
results. At 15MPH a Dutch bicycle (new) fitted with disk brakes
could stop in 5m, the web calculator claimed 2.6m.

The retardation for these distances is significantly below even your
pitchover figure.

The latest Highway code braking distances have been reduced somewhat
and appear to assume retardation of about 0.65g.This produces a
braking distance figure from 60MPH of 54m, a test by Which? on some
fairly average cars produced stopping distances at that speed between
34 and 44m.

The difference always looks dramatic on a side by side test but isn't
particularly real world significant. In the distance a 50's car took from
30mph, the best modern car can only start from 36mph before using up that
distance (including driver reaction).

Time to brake to stop is the speed in metres per second divided by the
deceleration rate. Cars can always decelerate more rapidly than
bicycles. There doesn't appear to be any doubt that a car can stop
more quickly than any bike at comparable speeds. In the rain the
disparity increases considerably.

If the dry limit for a bicycle is pitchover, in the wet it will be tyre
adhesion. The disparity reduces.

On Tue, 23 Feb 2016 09:39:43 -0000, "TMS320" wrote:

"Peter Parry" wrote

With a push bike rider skill is a far more important factor than with
a car Most riders are unable to achieve anything like the best the
cycle can brake at. The quality of the road surface also has a major
impact. The average rider rarely manages more than 0.35g.

Do you mean that an average rider rarely does more than 0.35g by routine? Or
has this figure been determined by putting a sample through controlled
stress tests?

Controlled tests on well maintained bikes with brakes front and rear
on dry surfaces. The riders were experienced "utility" cyclists.
Nearly all applied insufficient braking force as they feared the front
wheel would skid or they would be tipped over.

Many countries allow bikes with rear brake only - are you sure you're
not confusing two different things?

Would a rear brake alone be capable of 0.35g retardation: I would
have thought nearer 0.25g?

If it is 'by routine' then drivers rarely do more than 0.35g.

However, if we assume the surface is dry and pristine and the
pushbike is braking at the best the machine can achieve the limit for
the pushbike is not the adhesion of the tyre on the road but weight
transfer which can cause pitch over at about 0.6g (the subsequent
adhesion of shredded flesh to tarmac is not usually considered to be
part of stopping distance).

Pitchover is higher than 0.6g. Although there are techniques of improving
weight distribution to stop pitchover during deep braking, I expect most
cases are low speed when the rider puts feet down too soon.

"For an upright bicycle on dry asphalt with excellent brakes, pitching
will probably be the limiting factor. The combined center of mass of a
typical upright bicycle and rider will be about 60 cm (24 in) back
from the front wheel contact patch and 120 cm (47 in) above, allowing
a maximum deceleration of 0.5 g (5 m/s2 or 16 ft/s2).[28] If the rider
modulates the brakes properly, however, pitching can be avoided. If
the rider moves his weight back and down, even larger decelerations
are possible." (Wikipedia - Bicycle_and_motorcycle_dynamics).


0.67 seems to be about the absolute limit using extreme body
positioning (chest on saddle) well beyond what most riders are
capable of doing. The pitchover g force is reduced if the weight of
the rider moves forward due to insufficient bracing against the
handlebars (some authors consider this forward body movement to be the
most common reason for riders going over the front of the bike).

"High Speed Bicycling" (Wayne Pein, Bicycling Matters) says:-

"Four-wheeled motor vehicles have much better emergency braking
capabilities than bicycles, approximately 0.6 - 0.7 g (some cars can
achieve more than 0.9 g), affording motorists a great margin for error
beyond AASHTO’s roadway design specification. In contrast, a typical
bicyclist can be expected to decelerate at 0.35 g on clean, dry, level
pavement which, coincidentally, is AASHTO’s figure for roadway design
purposes as previously noted. A conventional bicycle's theoretical
maximum deceleration is limited to about 0.6 g on level pavement by
weight transfer, which can cause pitch-over. However, only a highly
skilled bicyclist using optimal technique may be able to achieve this
0.6 g; most will be far lower at about 0.35 g."

It would appear that the calculator you used at exploratorium.edu is
significantly wrong. For a speed of 24.85 MPH it gives a stopping
distance of 7.14m. A test of the Shimano R785 Hydraulic road disc
brakes at that speed for review produced stopping distances of 14m.
The Campagnolo Chorus calipers and alloy rims produced similar
results. At 15MPH a Dutch bicycle (new) fitted with disk brakes
could stop in 5m, the web calculator claimed 2.6m.

The retardation for these distances is significantly below even your
pitchover figure.

The latest Highway code braking distances have been reduced somewhat
and appear to assume retardation of about 0.65g.This produces a
braking distance figure from 60MPH of 54m, a test by Which? on some
fairly average cars produced stopping distances at that speed between
34 and 44m.

The difference always looks dramatic on a side by side test but isn't
particularly real world significant. In the distance a 50's car took from
30mph, the best modern car can only start from 36mph before using up that
distance (including driver reaction).

The latest Highway Code figures reduced the braking distance but
increased the thinking distance thus keeping the overall stopping
distance more or less unchanged. I'm only considering braking
distance here so the effectiveness of the brakes can be compared
without confounding factors. There is no doubt that a car can stop
more quickly than a pushbike.

There is also no doubt once braking hard a pushbike riders skill (or
not) is more of a factor than with the driver of a car who simply has
to press the brake hard.

Time to brake to stop is the speed in metres per second divided by the
deceleration rate. Cars can always decelerate more rapidly than
bicycles. There doesn't appear to be any doubt that a car can stop
more quickly than any bike at comparable speeds. In the rain the
disparity increases considerably.

If the dry limit for a bicycle is pitchover, in the wet it will be tyre
adhesion. The disparity reduces.

It is usually brake effectiveness (or lack of) which creates the wet
limit. A TRRL report from 1980 on rim brakes found that using
synthetic brake blocks on chromed steel wheel rims in the dry a
maximum retardation of 0.76g could be obtained, the same
brake/wheel/rider combination managed only 0.21g in the wet. For
alloy wheels the dry braking force was 0.46g dry and 0.39g wet.(TRRL
supplementary report 619). Although the report is old most pushbikes
still use caliper brakes and the results remain relevant. Moreover,
fear of skidding means many riders do not brake effectively in the
wet.

"Peter Parry" wrote in message
On Tue, 23 Feb 2016 09:39:43 -0000, "TMS320" wrote:
"Peter Parry" wrote

With a push bike rider skill is a far more important factor than with
a car Most riders are unable to achieve anything like the best the
cycle can brake at. The quality of the road surface also has a major
impact. The average rider rarely manages more than 0.35g.

Do you mean that an average rider rarely does more than 0.35g by routine?
Or
has this figure been determined by putting a sample through controlled
stress tests?

Controlled tests on well maintained bikes with brakes front and rear
on dry surfaces. The riders were experienced "utility" cyclists.
Nearly all applied insufficient braking force as they feared the front
wheel would skid or they would be tipped over.

It's still hard to tell whether it was an actual stress test or an
instruction "in your
own time come to a stop as quickly as you can".

Many countries allow bikes with rear brake only - are you sure you're
not confusing two different things?

Would a rear brake alone be capable of 0.35g retardation: I would
have thought nearer 0.25g?

Maybe.

...

It would appear that the calculator you used at exploratorium.edu is
significantly wrong. For a speed of 24.85 MPH it gives a stopping
distance of 7.14m. A test of the Shimano R785 Hydraulic road disc
brakes at that speed for review produced stopping distances of 14m.
The Campagnolo Chorus calipers and alloy rims produced similar
results. At 15MPH a Dutch bicycle (new) fitted with disk brakes
could stop in 5m, the web calculator claimed 2.6m.

The retardation for these distances is significantly below even your
pitchover figure.

The latest Highway code braking distances have been reduced somewhat
and appear to assume retardation of about 0.65g.This produces a
braking distance figure from 60MPH of 54m, a test by Which? on some
fairly average cars produced stopping distances at that speed between
34 and 44m.

The difference always looks dramatic on a side by side test but isn't
particularly real world significant. In the distance a 50's car took from
30mph, the best modern car can only start from 36mph before using up that
distance (including driver reaction).

The latest Highway Code figures reduced the braking distance but
increased the thinking distance thus keeping the overall stopping
distance more or less unchanged. I'm only considering braking
distance here so the effectiveness of the brakes can be compared
without confounding factors. There is no doubt that a car can stop
more quickly than a pushbike.

But you are introducing confounding factors when you talk about cyclists
only achieving 0.35g. And you haven't offered an explanation for why the
brakes you quote above fall well short of 0.6g. Is the limitation on bicycle
braking the actual brake power or pitchover? It can't be both.

There is also no doubt once braking hard a pushbike riders skill (or
not) is more of a factor than with the driver of a car who simply has
to press the brake hard.

There is also no doubt that cars are driven faster than bicycles are ridden
and a car might have to stop when there would be a gap for a bicycle to go
through.

Time to brake to stop is the speed in metres per second divided by the
deceleration rate. Cars can always decelerate more rapidly than
bicycles. There doesn't appear to be any doubt that a car can stop
more quickly than any bike at comparable speeds. In the rain the
disparity increases considerably.

If the dry limit for a bicycle is pitchover, in the wet it will be tyre
adhesion. The disparity reduces.

It is usually brake effectiveness (or lack of) which creates the wet
limit. A TRRL report from 1980 on rim brakes found that using
synthetic brake blocks on chromed steel wheel rims in the dry a
maximum retardation of 0.76g could be obtained, the same
brake/wheel/rider combination managed only 0.21g in the wet. For
alloy wheels the dry braking force was 0.46g dry and 0.39g wet.(TRRL
supplementary report 619). Although the report is old most pushbikes
still use caliper brakes and the results remain relevant. Moreover,
fear of skidding means many riders do not brake effectively in the
wet.

Riding in the wet does not necessarily mean the rims get wet. And the
numbers above are inconsistent:- dry braking for steel 0.76g, alloy 0.46g.
Eh? Add that to all the above and we are no better informed than before we
started.

On Sun, 21 Feb 2016 11:14:23 -0800 (PST), Alycidon
wrote:

If the figures above are correct, the bike has enough braking power to brake in half the distance of a 'standard' car."

a. The figures are not correct

b. It can't

On Sunday, 21 February 2016 13:48:12 UTC, MrCheerful wrote:
Just out of interest I found probably the same info. that the Collision
investigators use to calculate braking distances for bicycles. The
distance from perception to stop at 30kph (just under 20mph) is 37m on a
level road. Metric and imperial versionss are both shown.

http://www.muggaccinos.com/Liability...opFormulae.htm

For a car the distance is 12.6m ( thinking plus braking )

On Thursday, 14 May 2020 13:37:43 UTC+1, wrote:
On Sunday, 21 February 2016 13:48:12 UTC, MrCheerful wrote:
Just out of interest I found probably the same info. that the Collision
investigators use to calculate braking distances for bicycles. The
distance from perception to stop at 30kph (just under 20mph) is 37m on a
level road. Metric and imperial versionss are both shown.

http://www.muggaccinos.com/Liability...opFormulae.htm

For a car the distance is 12.6m ( thinking plus braking )

OMGods how did this resurface.