Re: Non-invasive Pressure Gauge?

hm.

it seems, after looking at their site, that
a durometer fires a weight from a spring, then measures
the resulting bounce back, in a standard hardness scale.

in fact you usually use it to test rubbers and plastics.

but they expect you to use a thick sample of the material, resting
on a solid
surface.

the gauge i want would actually have to ignore the rubber somehow and
just
test the air pressure. the problem is that the stiffness of the rubber
would
add to the apparent air pressure reading, and you would not know how to

compensate unless you calibrated for each tire type, or unless that is
actually
a minor effect.

imagine a normal balloon under test.
then imagine something like a car tire.
the stiffness of the rubber in the car tire would make readings
different from something
thin like a balloon.

anyway, i wrote to them to see if there is a way to use it.

though they cost $250 minimum.

obviously i want something around $10.

wle.

"wle" wrote: (clip) the gauge i want would actually have to ignore the
rubber somehow and just test the air pressure. the problem is that the
stiffness of the rubber would add to the apparent air pressure reading, and
you would not know how to compensate unless you calibrated for each tire
type, or unless that is actually a minor effect. imagine a normal balloon
under test. then imagine something like a car tire. the stiffness of the
rubber in the car tire would make readings different from something thin
like a balloon (clip)
^^^^^^^^^^^^^^^^
Yes, Durometer. It uses a rounded metal plunger to indent the rubber
surface, just as your thumb does, and measures the indentation with a dial
gauge. I have never heard of one which fires a weight.

But, the main point I am trying to stress is that the OUTSIDE of the tire is
in contact with the road. Tire pressure measurement is an INDIRECT method
of controlling the way the tire flattens in contact with the pavement. A
Durometer measures that directly, so it would not be necessary to know the
pressure (except to know that the tire is not going to explode, or fly off
the rim.) I am thinking that if you inflated your tires to a certain
Durometer hardness, you would get the desired rolling resistance and
traction MORE directly than you do by looking at pressure. Variations in
rubber stiffness would be included in the measurement, so the result should
be more representative the the way the tire behaves, not less.

As to cost: if the idea is found to work, it is likely that gauges could be
manufactured in a price range comparable to air pressure gauges. The
present high price of Durometer gauges is due to the fact that they are
laboratory instruments, produced and sold in limited quantities.

I think this is a real pregnant idea!

Leo Lichtman said:

"wle" wrote: (clip) the gauge i want would actually have to ignore the
rubber somehow and just test the air pressure. the problem is that the
stiffness of the rubber would add to the apparent air pressure reading, and
you would not know how to compensate unless you calibrated for each tire
type, or unless that is actually a minor effect. imagine a normal balloon
under test. then imagine something like a car tire. the stiffness of the
rubber in the car tire would make readings different from something thin
like a balloon (clip)
^^^^^^^^^^^^^^^^
Yes, Durometer. It uses a rounded metal plunger to indent the rubber
surface, just as your thumb does, and measures the indentation with a dial
gauge. I have never heard of one which fires a weight.

But, the main point I am trying to stress is that the OUTSIDE of the tire is
in contact with the road. Tire pressure measurement is an INDIRECT method
of controlling the way the tire flattens in contact with the pavement. A
Durometer measures that directly, so it would not be necessary to know the
pressure (except to know that the tire is not going to explode, or fly off
the rim.) I am thinking that if you inflated your tires to a certain
Durometer hardness, you would get the desired rolling resistance and
traction MORE directly than you do by looking at pressure. Variations in
rubber stiffness would be included in the measurement, so the result should
be more representative the the way the tire behaves, not less.

As to cost: if the idea is found to work, it is likely that gauges could be
manufactured in a price range comparable to air pressure gauges. The
present high price of Durometer gauges is due to the fact that they are
laboratory instruments, produced and sold in limited quantities.

I think this is a real pregnant idea!

I use an instrument every day that determines the internal pressure of
living human eyes by examination of the "footprint" as the instrument
leans against the wall of the eye. [It's called an applanation
tonometer.]

Like various tires, various eyes also have some differences in stiffness
of their casings, and of course this cause a variance between the
measured pressure and the actual pressure. To compensate for that, the
thickness of the cornea, where the pressure measurement is taken, can be
measured ultrasonically, and an adjustment can be made to the
intraocular pressure measurement for more accuracy.

Tires have far higher pressures than eyeballs, but Leo's idea would work
fine. I could envision making the measurement by being able to see the
contact patch and compare it with a template representing the ideal
patch, if such a thing exists, for the application.

--
Ted Bennett
Portland, OR

"Ted" wrote: (clip) I could envision making the measurement by being able
to see the contact patch and compare it with a template representing the
ideal patch,(clip)
^^^^^^^^^^^^^^^^
Neat! Here's how I propose doing it: With the tire inflated to the desired
pressure, press a piece of plate glass against the tread with a reproducible
force. Look through the glass at the contact patch, and outline it with a
wax pencil. Next time you want to check the inflation, put the glass back,
with the same force, and compare the new contact patch with the tracing of
the old one.

I'm not claiming that this is simpler than using a pressure gauge. I'm just
trying to demonstrate that the principle is do-able.