Tire Gauge?

> > Where does one find a "quality" one then? Many of the dial-type
> > or digital readout gauges tend to be more accurate than the easy
> > to find pen-type gauges.

I've got a nice dial type made by AccuGage that I bought for about $15 or so
from Sporty's Tool Shop (www.sportys.com) Its attachment goes straight in
line with the valve stem, so no valve extensions are neccesary. It is
encased in hard rubber. 0-60 lbs range. Nice....

On Mon, 24 Jan 2005, HLS wrote:

> > Good gauges are better than bad gauges, period. There's no
> > manufactured product that MBAs can't entice the Chinese to make a
> > little cheaper and a little ****tier.

> The statement I quibble with is that a stick type gauge can inherently
> be as reproducible and accurate as a Bourdon type, assuming equal
> quality of manufacturing.

Quibble all you like. Reality has a nasty habit of shooting ugly holes in
beautiful theories.

"Daniel J. Stern" > wrote in message
.umich.edu...
..
>
> Quibble all you like. Reality has a nasty habit of shooting ugly holes in
> beautiful theories.


It isnt a theory, Light Bulb Boy. Just the truth.

>y_p_w wrote
>However - my experience is that they (stick gauges) don't always
>shoot to the same point every time - even the good ones.

That's always been my complaint.


I am addicted to dial gauges. Many years ago I took my collection of assorted
tire gauges with me on a trip to Akron and tested their accuracy at one of the
tire research & testing facilities where I had once worked. The dial gauges
were consistently more accurate and more precise. I identified the gauge which
was the best and I have carefully protected it for years as my reference gauge
for calibrating others. I kept the dial gauges and labeled them on the back
(eg: Reads + 1/2 psi). I gave away all of the stick gauges.

A note or two on evaluating gauges. Suppose that you have two gauges and you
test each one of them 10 times in an attempt to measure a particular psi:
1) Take the average reading for gauge A over 10 tests and the average reading
for gauge B over 10 tests. If the average psi reading for gauge A is closer to
the actual psi, then gauge A is more "accurate" than gauge B. Accuracy is a
measure of how probable the gauge is to give a correct reading.
2) Now, for gauge A look at the deviation from the true psi for each of the 10
readings. Just use the absolute value of the deviation, ignoring plus or
minus. Thus a reading that is off by -0.75 psi would have an absolute
deviation of 0.75. Sum these 10 deviations. Do the same for gauge B. If the
sum of deviations for gauge A is less than for gauge B, then gauge A is said to
be more "precise" than gauge B. Precision is a measure of how consistent a
gauge is with its readings.

Precision is the important criteria for selecting a tire gauge. It is the true
measure of how well the gauge was manufactured. A gauge which is very precise
but not particularly accurate can be recalibrate to be both precise and
accurate. The opposite is not true.

A gauge which is precise can be recalibrated the lazy way that I use - just
put a piece of tape on the back indicating how high or low it tends to read.
Or you can do it properly by opening the gauge and recalibrating physically.

Analogies:
1) Consider ruler A which is extremely well machined and has laser etched
gradients down to 1/1000" of an inch. But the ruler scale runs from 1" to 13"
rather than the standard 0" to 12". Also, consider ruler B which is one of
those cheap 25 cent plastic rulers used by students. Measurements taken with
ruler A will always but much less accurate than those taken with the cheap
ruler B. But it is obvious that ruler A is a much more precise device which
you can easily "recalibrate" to give superior measurements compared to ruler B.

2) Consider 2 pistols which are new-in-the-box. The more poorly manufactured
pistol may be more accurate when you first use it. But the better built one
will probably be more precise and after a bit of sighting-in at the range, you
will have it adjusted to be the more accurate of the two. It may have started
off producing nice tight patterns off to the edge of the target. This is no
concern to the experience shooter who knows that he can adjust the sights to
move that pattern over top the bullseye.

>Daniel J. Stern wrote
>Quibble all you like. Reality has a nasty habit of shooting
>ugly holes in beautiful theories.

Reality does shoot holes in theory sometimes, but fortunately
that is the exception rather than the rule.

What sort of gauge is being used by the folks who demand
accuracy? You local tire retail outlet, gas station or auto
service center don't count - being accurate within a few PSI
is generally considered adequate for them.

I'd look to the following:
- The tire R&D field, which I've said only uses dial gauges
by my observations. There are many tires tests which
are very sensitive to proper inflation - braking, resonant
frequency, tire uniformity, traction, endurance ("run to
failure" testing), etc. The testers use dial gauges.
- Commercial & military aircraft. I don't know about
this one.
- Serious auto racers. The few that I know wouldn't touch
a stick gauge, and this includes one acquaintence who
is very fussy about tire pressures for his Shelby Cobra
and and his Indy car.
- HVAC manifold/gauge sets. I've never seen a pop-up style
gauge on an AC manifold set. I've got 3 sets and they've
all got dial gauges. To me, the high pressure gauge is
mostly a "sanity check" and I could live with rough
appoximations there, but I want accuracy to less than
1 psi on the low side readings.
- Oxy-Acetylene manifold/gauge sets. Mine has dial gauges
and so do all the sets that I've ever seen.

Gideon