Hydroplaning: the experiment.

A main reason why jet aircraft use high tire pressures is to raise the
hydroplaning speed so that it's easier to control the aircraft on
landing rollout.

The classical hydroplaning on standing water, called dynamic
hydroplaning, can occur when the speed in knots exceeds 9 times the
square root of the tire pressure in psi.

Another type, called viscous hydroplaning, can occur at MUCH lower
speeds on surfaces contaminated with dust, oil, etc.

Michael Press said:

Method: Support the bicycle at the bottom bracket a few
centimeters higher than the bottom bracket height so that the
bicycle rotates on the this support. The bicycle can be rotated so
that the rear wheel is not in contact with the pavement; or can be
rotated so that the rear wheel is in contact with the pavement.
Run water from a garden hose on the pavement where the rear tire
is in contact with the pavement. Rotate the bicycle so that the
rear wheel is not in contact with the pavement. Put the bicycle
in its highest gear, rotate the crank to 120rpm or faster, then
rotate the bicycle about the bottom bracket support so that the
spinning rear tire is in contact with the inundated pavement.

I'll preface my comment with my assumption that no normal bicycle can
hydroplane at any speed attainable by a bicycle.

However, your experiment is not valid in proving that point. Even a
car would exhibit the behavior you observed, and cars are known to
hydroplane.

It is the surface speed of the vehicle, and not the mere presence of
water, that allows hydroplaning. In your experiment, the surface speed
was zero. Even the "surface speed" of the flowing water itself could
not have been very high. So while your willingness to experiment is
commendable, your particular experiment does not support either side of
the dispute.

Chalo Colina

Chalo said:

Michael Press said:

Method: Support the bicycle at the bottom bracket a few
centimeters higher than the bottom bracket height so that the
bicycle rotates on the this support. The bicycle can be rotated so
that the rear wheel is not in contact with the pavement; or can be
rotated so that the rear wheel is in contact with the pavement.
Run water from a garden hose on the pavement where the rear tire
is in contact with the pavement. Rotate the bicycle so that the
rear wheel is not in contact with the pavement. Put the bicycle
in its highest gear, rotate the crank to 120rpm or faster, then
rotate the bicycle about the bottom bracket support so that the
spinning rear tire is in contact with the inundated pavement.

I'll preface my comment with my assumption that no normal bicycle can
hydroplane at any speed attainable by a bicycle.

However, your experiment is not valid in proving that point. Even a
car would exhibit the behavior you observed, and cars are known to
hydroplane.

It is the surface speed of the vehicle, and not the mere presence of
water, that allows hydroplaning. In your experiment, the surface speed
was zero. Even the "surface speed" of the flowing water itself could
not have been very high. So while your willingness to experiment is
commendable, your particular experiment does not support either side of
the dispute.

The experiment sounds a little like trying to throw a lake at a rock
to see if it'll skip. ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

it is true that a bike will not hydroplane at any attainable speed.

though your experiment also falls short by not considering that one
can coast faster than one can pedal at 120 rpm in high gear.

it also does not account for the weight on the tire.

but, on the subject of hydroplaning in general..:

i don;t know how hydroplanability varies with relative tire hardness,
but
a car typically has 3000 lbs, divided by 4 wheels, 750 lbs weight.

typical air pressure of 30 psi puts the ratio at 750/30=25 load lbs per
tire psi.

typical bike number would be 100 divided by 120 = .83 load lbs per tire
psi.

25/.83 is a factor of 30..

again i am not sure how it relates to hydroplanability but a car tire
is a hell of a lot
fatter and softer than a bike tire.

wle.

Michael Press said:

Method: Support the bicycle at the bottom bracket a few
centimeters higher than the bottom bracket height so that the
bicycle rotates on the this support. The bicycle can be rotated so
that the rear wheel is not in contact with the pavement; or can be
rotated so that the rear wheel is in contact with the pavement.
Run water from a garden hose on the pavement where the rear tire
is in contact with the pavement. Rotate the bicycle so that the
rear wheel is not in contact with the pavement. Put the bicycle
in its highest gear, rotate the crank to 120rpm or faster, then
rotate the bicycle about the bottom bracket support so that the
spinning rear tire is in contact with the inundated pavement.

Result: The wheel decelerates to 0 rpm in less than 1 second.
Rubber is scrubbed off the tire and is visible as it is washed
away.

Conclusion: The bicycle tire does not hydroplane at the highest
speed attainable by a racing cyclist.

Note: I conducted this experiment with a slick tire.

The pavement was not moving, ergo your simulation is flawed. The
relative speed of the tire's contact patch to the road surface must be
zero for the simulation to apply.

(There are many ways to devise a test which, though faulty, provides
results which appear valid. Do not be surprised that you fiound one.
Good try, none the less.)
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

wle said:

it is true that a bike will not hydroplane at any attainable speed.

though your experiment also falls short by not considering that one
can coast faster than one can pedal at 120 rpm in high gear.

it also does not account for the weight on the tire.

but, on the subject of hydroplaning in general..:

i don;t know how hydroplanability varies with relative tire hardness,
but
a car typically has 3000 lbs, divided by 4 wheels, 750 lbs weight.

typical air pressure of 30 psi puts the ratio at 750/30=25 load lbs
per tire psi.

typical bike number would be 100 divided by 120 = .83 load lbs per
tire psi.

25/.83 is a factor of 30..

How does this matter at all? The contact patch of a car runs laterally
(primed for hydroplaning) and the contact patch of 2-wheeled vehicles runs
longitudinally (parting the red sea).

--
Phil, Squid-in-Training

it only 'runs laterally' because it;s so big in the first place.

i think the shape doesn;t matter anyway, just size and weight per unit
area.

wle.

wle said:

it only 'runs laterally' because it;s so big in the first place.

i think the shape doesn;t matter anyway, just size and weight per unit
area.

wle.

Why don't we have knife-edge water skis?

--
Phil, Squid-in-Training

On 25 May 2005 19:35:38 -0700, "wle" <[email hidden]>

Quoted message said:

it is true that a bike will not hydroplane at any attainable speed.

though your experiment also falls short by not considering that one
can coast faster than one can pedal at 120 rpm in high gear.

it also does not account for the weight on the tire.

but, on the subject of hydroplaning in general..:

i don;t know how hydroplanability varies with relative tire hardness,
but
a car typically has 3000 lbs, divided by 4 wheels, 750 lbs weight.

typical air pressure of 30 psi puts the ratio at 750/30=25 load lbs per
tire psi.

typical bike number would be 100 divided by 120 = .83 load lbs per tire
psi.

25/.83 is a factor of 30..

again i am not sure how it relates to hydroplanability but a car tire
is a hell of a lot
fatter and softer than a bike tire.

wle.

Dear WLE,

It does seem odd, but the main variables in hydroplaning is
simply the tire inflation pressure (softness) and the speed
of the water relative to the surfaces.

A tire's contact patch depends on the weight that it
supports and its inflation.

A 100 lb weight on 20 psi tires has 5 square inches of
contact patch.

A 200 lb weight on 20 psi tires has 10 square inches of
contact patch--and it's all still at 20 psi.

A 50 lb weight on 20 psi tires has 2.5 square inches of
contact patch--and it's all still at 20 psi.

When the pressure of the water (a function of the speed
relative to the tire and ground) rises to 20 psi, the water
forces its way between the tire and ground and supports the
tire--you have to have 20 psi in the water to support the 20
psi of the tire pressure.

With a flat section car-style tire, it doesn't matter if the
tire is 4 inches wide or 40--with 30 psi, both tires
(rolling) will start to hydroplane somewhere around the
speed in knots that equals nine times the square root of the
tire pressure in psi:

rolling tire Knots = 9 * sqrt(psi)
43 mph = 9 * sqrt(30)

When a motionless tire is slapped down onto a wet runway,
hydroplaning begins earlier--7.7 instead of 9:

static tire Knots = 7.7 * sqrt(psi)
37 mph = 7.7 * sqrt(30)

Water grooves can delay the onset of hydroplaning, if
they're deep enough compared to the depth of the water.

Rolling touring bicycle tires at 80 to 120 psi will start to
hydroplane around 70 to 86 mph, much faster than any
ordinary wet-weather riding speed. They are also more
resistant because they aren't flat, but curved, presenting
more of a Vee to the oncoming water.

Carl Fogel

"Phil, Squid-in-Training" <[email hidden]>

Quoted message said:

Why don't we have knife-edge water skis?

Like there aren't already enough ways to get hurt water skiing?
;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

Mark Hickey said:

"Phil, Squid-in-Training" <[email hidden]>

Quoted message said:

Why don't we have knife-edge water skis?

Like there aren't already enough ways to get hurt water skiing?
;-)

I have problems just trying to hang on!

--
Phil, Squid-in-Training

[email hidden] wrote in news:drlc919etgg0usk9frppebitvfvfgltm8k@
4ax.com:

Quoted message said:

Dear WLE,

It does seem odd, but the main variables in hydroplaning is
simply the tire inflation pressure (softness) and the speed
of the water relative to the surfaces.

A tire's contact patch depends on the weight that it
supports and its inflation.

A 100 lb weight on 20 psi tires has 5 square inches of
contact patch.

A 200 lb weight on 20 psi tires has 10 square inches of
contact patch--and it's all still at 20 psi.

A 50 lb weight on 20 psi tires has 2.5 square inches of
contact patch--and it's all still at 20 psi.

When the pressure of the water (a function of the speed
relative to the tire and ground) rises to 20 psi, the water
forces its way between the tire and ground and supports the
tire--you have to have 20 psi in the water to support the 20
psi of the tire pressure.

With a flat section car-style tire, it doesn't matter if the
tire is 4 inches wide or 40--with 30 psi, both tires
(rolling) will start to hydroplane somewhere around the
speed in knots that equals nine times the square root of the
tire pressure in psi:

rolling tire Knots = 9 * sqrt(psi)
43 mph = 9 * sqrt(30)

When a motionless tire is slapped down onto a wet runway,
hydroplaning begins earlier--7.7 instead of 9:

static tire Knots = 7.7 * sqrt(psi)
37 mph = 7.7 * sqrt(30)

Water grooves can delay the onset of hydroplaning, if
they're deep enough compared to the depth of the water.

Rolling touring bicycle tires at 80 to 120 psi will start to
hydroplane around 70 to 86 mph, much faster than any
ordinary wet-weather riding speed. They are also more
resistant because they aren't flat, but curved, presenting
more of a Vee to the oncoming water.

Carl Fogel

Dear Carl,

While I agree with most of your assessment, your math regarding the
calculated contact patches is ultimately flawed.
A tire is not a latex baloon, it has its own rigidity and stiffness and
merely dividing the load applied to a wheel by the tire's pressure would
in no way give you the contact patch area. This time I think you
outsmarted yourself.
Please, find some reference material, read it, educate yourself on the
subject and then report back to the newsgroup.
Keep in mind that the matter gets further complicated by tire pressure
being temperature (hence speed) sensitive.
Later,
IK

IK said:

Keep in mind that the matter gets further complicated by tire pressure
being temperature (hence speed) sensitive.

Not very much. The change in pressure is proportional to the change in
_absolute_ temperature. The total operating temperature range is quite
small in comparison, less than 10% of absolute temperature even in a
car tire. In a bicycle tire, the pressure change from speed-induced
heating is negligible.

A change in tire temperature has a much more pronounced effect on the
hardness of the tread rubber though, and this changes the
characteristics of the contact patch by altering the pressure gradient
within it.

Chalo Colina

Mark Hickey said:

"Phil, Squid-in-Training" <[email hidden]>

Quoted message said:

Why don't we have knife-edge water skis?

Like there aren't already enough ways to get hurt water skiing?

Stupidest thing I ever did (well...) was trying water skiing with my
chronically bad right shoulder (one operation at the time; second since). I
so over protected it I wrecked the LEFT one!

From now on I drive the boat.

Dry Bill

IK said:

[email hidden] wrote in news:drlc919etgg0usk9frppebitvfvfgltm8k@
4ax.com:

Quoted message said:

Dear WLE,

It does seem odd, but the main variables in hydroplaning is
simply the tire inflation pressure (softness) and the speed
of the water relative to the surfaces.

A tire's contact patch depends on the weight that it
supports and its inflation.

A 100 lb weight on 20 psi tires has 5 square inches of
contact patch.

A 200 lb weight on 20 psi tires has 10 square inches of
contact patch--and it's all still at 20 psi.

A 50 lb weight on 20 psi tires has 2.5 square inches of
contact patch--and it's all still at 20 psi.

When the pressure of the water (a function of the speed
relative to the tire and ground) rises to 20 psi, the water
forces its way between the tire and ground and supports the
tire--you have to have 20 psi in the water to support the 20
psi of the tire pressure.

With a flat section car-style tire, it doesn't matter if the
tire is 4 inches wide or 40--with 30 psi, both tires
(rolling) will start to hydroplane somewhere around the
speed in knots that equals nine times the square root of the
tire pressure in psi:

rolling tire Knots = 9 * sqrt(psi)
43 mph = 9 * sqrt(30)

When a motionless tire is slapped down onto a wet runway,
hydroplaning begins earlier--7.7 instead of 9:

static tire Knots = 7.7 * sqrt(psi)
37 mph = 7.7 * sqrt(30)

Water grooves can delay the onset of hydroplaning, if
they're deep enough compared to the depth of the water.

Rolling touring bicycle tires at 80 to 120 psi will start to
hydroplane around 70 to 86 mph, much faster than any
ordinary wet-weather riding speed. They are also more
resistant because they aren't flat, but curved, presenting
more of a Vee to the oncoming water.

Carl Fogel

Dear Carl,

While I agree with most of your assessment, your math regarding the
calculated contact patches is ultimately flawed.
A tire is not a latex baloon, it has its own rigidity and stiffness and
merely dividing the load applied to a wheel by the tire's pressure would
in no way give you the contact patch area. This time I think you
outsmarted yourself.
Please, find some reference material, read it, educate yourself on the
subject and then report back to the newsgroup.
Keep in mind that the matter gets further complicated by tire pressure
being temperature (hence speed) sensitive.
Later,
IK

Dear IK,

If the air inside the tire is pushing out at 100 psi, how
hard must the water push back on the tire to raise it off
the ground?

Yes, the details of hydroplaning become quite tricky, but
the basics seem to argue that the huge tire pressure of a
bicycle tire would prevent it from aquaplaning even if it
were flat, and the <:::::> shape of the contact patch makes
it even more unlikely to hydroplane.

For hydroplaning, the tire pressure isn't much affected by
ordinary temperatures--32F to 61F to 90F is about as much as
can be reasonably expected, which is 492 to 521 to 550
Rankine, the absolute Fahrenheit scale. (I don't feel like
Kelvin tonight.)

A car tire inflated to 30 psi at 61 degrees (midway between
the two extremes) would hit icy water in freezing weather at
28.3 psi and 90 degree water in a steamy monsoon at 31.6
psi. The theoretical hydroplane speed for a rolling tire
would vary only 2.4 mph as shown below:

Rankine 492 521 550
F 32 61 90
PSI 28.3 30.0 31.6
hydro mph 41.6 42.8 44.0

For a touring bicycle's larger pressures, the variation in
pressure and hydroplaning speed would be larger, but still
considerably beyond any normal speed--80 psi needs 70 mph to
hydroplane on a flat tire and even more on a curved cross
section tire.

Carl Fogel

weight per unit area would sink that idea...

note that skis turned sideways would hydroplane equally well though
perhaps not be very guidable..

wle.

IK said:

A tire is not a latex baloon, it has its own rigidity and stiffness and
merely dividing the load applied to a wheel by the tire's pressure would
in no way give you the contact patch area.

There's a simple experiment you can do to assess the stiffness of the
tire casing compared to the stiffness of the inflated tire. Take a
normal, fully inflated tire and squeeze it with your thumb. Now let all
of the air out and squeeze it again. After you've done this, I think
you'll agree that the dominant spring in the system is the inflated air
chamber.

Once that concept is understood, you can probably see that the average
contact patch area between a tire and a smooth surface is simply
force/pressure. Of course, no road is perfectly smooth, but the surface
of a puddle is pretty darn smooth.

--
Dave
dvt at psu dot edu

Bill Sornson said:

Mark Hickey said:

"Phil, Squid-in-Training" <[email hidden]>

Quoted message said:

Why don't we have knife-edge water skis?

Like there aren't already enough ways to get hurt water skiing?

Stupidest thing I ever did (well...) was trying water skiing with my
chronically bad right shoulder (one operation at the time; second
since). I so over protected it I wrecked the LEFT one!

At first I thought you said that you were trying to water ski ON your
chronically bad right shoulder.

--
Phil, Squid-in-Training

IK said:

dvt <[email hidden]> wrote in news:[email hidden]:

Quoted message said:

IK said:

A tire is not a latex baloon, it has its own rigidity and stiffness
and merely dividing the load applied to a wheel by the tire's
pressure would in no way give you the contact patch area.

Quoted message said:

Quoted message said:

...you can probably see that the average
contact patch area between a tire and a smooth surface is simply
force/pressure.

Quoted message said:

Carl was referring to car tires with his ~20 psi pressures, and car tire
stiffness is quite a different animal.

You're right -- Carl referred to both car tires and bicycle tires in his
post. You didn't specify which part you disagreed with (a little
snippage might have prevented this misunderstanding).

--
Dave
dvt at psu dot edu