Silca pump gauge repair how-to

On Sat, 03 Sep 2016 07:32:38 +0700, John B.
wrote:

My experience is that most of the small cheap gauges do have errors,
but I would also guess that the average cyclists doesn't actually
care.

I have a cute trick that sometimes gets their attention. This really
only works with a floor pump. Pump up a tire to some particular
pressure and stop. Read the gauge as accurately as possible. Now,
squeeze the tire on the sides to increase the pressure. For narrow
high pressure tires, it may be necessary use a pair of pliers,
C-clamp, or anything that will produce a visible increase in pressure.
Sitting on the bike will usually do the tricks. Release the clamp or
get off the bike and read the gauge again.

On the few floor pump gauges that I've done this on, I can usually get
about 1 to 3 lb difference in reading. The hysteresis effect is more
obvious on low tire pressures than on high pressures. I once found an
ancient gauge that produced a 5 lb difference at about 45 lbs.

You can also do it from the other direction. If you fill a tire with
air and watch the gauge, the reading starts out high while pumping,
and then drops a little when you stop pumping. That's approaching the
final value from above (high - low). However, when you just apply a
tire pressure gauge to the tire, the final value is approached from
below (low - high). Assuming no leaks, the difference between the
two is the hysteresis of the gauge.

Another fun test is to measure the tire pressure when cold. Then, go
for a ride and measure it again when warm.

Of course, there's been some research:
http://velonews.competitor.com/2014/12/bikes-and-tech/resistance-futile-tire-pressure-width-affect-rolling-resistance_355085
Scroll down to "Inflation pressure versus rolling resistance". The
largest change in rolling resistance was 1.6 watts out of about 48
watts or about 3% overall. Not a big deal.

The consensus seems to be don't bother:
https://janheine.wordpress.com/2015/01/26/the-tire-pressure-revolution/
Of all our research on tires, the most revolutionary
finding is this: Tire pressure has almost no effect
on a tire’s speed. We did not believe it at first,
either, so we’ve tested it numerous times. It’s been
confirmed numerous times, with different methodologies.
(The reader comments are quite interesting and worth reading).

My guess is that the average guy pumps the tires up to a number
between the big number and the little number embossed on the tire wall
and rides away contented.

I guess I'm below average. I overpressure by about 10 psi, and let
the tire and valve leak air along my ride. I usually arrive with
insufficient pressure, but the average pressure along the ride is
about right.

At least, even here, there was sufficient discussion when the subject
came up to show, I believe that even the elite riders really aren't
really that knowledgeable about the effects of tire pressure.

I vaguely recall one discussion in this newsgroup on the pressure loss
caused by disconnecting the pump head. The OP apparently thought is
was sufficiently significant to worry about. I thought differently,
but managed to feed the fire sufficiently to keep the discussion going
for about a week.

But having said that, snake bite flats aside, what is the actual
importance of tire pressure? What will be the actual (not calculated)
difference in time for a, say 10 mile TT, with 10 psi more or less
pressure in the tires?

Sorry. No data, clue, or experience. I can only estimate the effect.
What might be useful is recording the times and tire pressures of all
the bicycles that cross the finish line after a race and see if there
is any correlation. However, due to the measurement errors and
uncontrolled conditions, the results will probably be meaningless.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 9/1/2016 12:17 PM, Tim McNamara wrote:


Well, putting the screw back in was easy. I popped the plastic bezel
off, reset the pointer to rest against the stop, put the bezel back on
and tried pumping up a tire. The pump seems to work fine and to read
fairly accurately. 105 PSI on the Silca gauge corresponded to 102 PSI
on another hand-held gauge that I have. Of course I don't know the
absolute calibration of either and those two gauges have never perfectly
matched anyway; about the same as this.

A few years ago, I used a laboratory dead weight pressure tester to
check the calibration on my collection of tire pressure gauges. To my
surprise, the most accurate were the pencil-style gages, the ones based
on a simple coil spring and piston. My floor pump (an ancient metal
Nashbar model with bourdon tube gage) was off by 7 psi, reading 100 psi
at a true 93 psi. A pocket sized Zefal gage with a dial was off by
nearly as much.

It is possible to calibrate bourdon tube gages, but I just used a magic
marker to write "Add 7 psi" on the side of the pump. Really, even a 7
percent discrepancy makes little difference when riding.

--
- Frank Krygowski

On 9/2/2016 12:05 PM, Jeff Liebermann wrote:


I wonder if the LBS could use this as a draw for the local cyclists.
Free bicycle pump gauge calibration. Bring in the pump, we supply the
equipment, and you do all the work. I suspect a fair number of pump
gauges have problems.
https://www.google.com/search?q=bicycle+pump+pressure+calibration

Some years ago, our bike club ran a sort of picnic-plus-ride event at a
local park, which included several bike-oriented games. In addition to
a slow bike race, a heaviest bike award, a bicycle rim toss game, etc.
we had a tire pumping contest.

Each contestant started with his own deflated tire and his own pump. The
objective was to pump the tire to 100 psi without using a gage. As I
recall, there were several people who got within just a couple psi... at
least, according to the not-officially-calibrated gage we used!

Further off-topic: Another contest was a flat tire changing race,
starting with a deflated front tire on a bike. The objective was to
pull the wheel, completely remove the tube, then replace it, remount the
tire, inflate to riding pressure and remount the wheel. The winner (a
guy who has the reputation of being the best pro bike mechanic in our
area) completed the task in less than a minute. Nobody else came close.

--
- Frank Krygowski

On Fri, 02 Sep 2016 18:29:32 -0700, Jeff Liebermann
wrote:

On Sat, 03 Sep 2016 07:32:38 +0700, John B.
wrote:

My experience is that most of the small cheap gauges do have errors,
but I would also guess that the average cyclists doesn't actually
care.

I have a cute trick that sometimes gets their attention. This really
only works with a floor pump. Pump up a tire to some particular
pressure and stop. Read the gauge as accurately as possible. Now,
squeeze the tire on the sides to increase the pressure. For narrow
high pressure tires, it may be necessary use a pair of pliers,
C-clamp, or anything that will produce a visible increase in pressure.
Sitting on the bike will usually do the tricks. Release the clamp or
get off the bike and read the gauge again.

On the few floor pump gauges that I've done this on, I can usually get
about 1 to 3 lb difference in reading. The hysteresis effect is more
obvious on low tire pressures than on high pressures. I once found an
ancient gauge that produced a 5 lb difference at about 45 lbs.

You can also do it from the other direction. If you fill a tire with
air and watch the gauge, the reading starts out high while pumping,
and then drops a little when you stop pumping. That's approaching the
final value from above (high - low). However, when you just apply a
tire pressure gauge to the tire, the final value is approached from
below (low - high). Assuming no leaks, the difference between the
two is the hysteresis of the gauge.

Another fun test is to measure the tire pressure when cold. Then, go
for a ride and measure it again when warm.

Of course, there's been some research:
http://velonews.competitor.com/2014/12/bikes-and-tech/resistance-futile-tire-pressure-width-affect-rolling-resistance_355085
Scroll down to "Inflation pressure versus rolling resistance". The
largest change in rolling resistance was 1.6 watts out of about 48
watts or about 3% overall. Not a big deal.

The consensus seems to be don't bother:
https://janheine.wordpress.com/2015/01/26/the-tire-pressure-revolution/
Of all our research on tires, the most revolutionary
finding is this: Tire pressure has almost no effect
on a tire’s speed. We did not believe it at first,
either, so we’ve tested it numerous times. It’s been
confirmed numerous times, with different methodologies.
(The reader comments are quite interesting and worth reading).

My guess is that the average guy pumps the tires up to a number
between the big number and the little number embossed on the tire wall
and rides away contented.

I guess I'm below average. I overpressure by about 10 psi, and let
the tire and valve leak air along my ride. I usually arrive with
insufficient pressure, but the average pressure along the ride is
about right.

At least, even here, there was sufficient discussion when the subject
came up to show, I believe that even the elite riders really aren't
really that knowledgeable about the effects of tire pressure.

I vaguely recall one discussion in this newsgroup on the pressure loss
caused by disconnecting the pump head. The OP apparently thought is
was sufficiently significant to worry about. I thought differently,
but managed to feed the fire sufficiently to keep the discussion going
for about a week.

But having said that, snake bite flats aside, what is the actual
importance of tire pressure? What will be the actual (not calculated)
difference in time for a, say 10 mile TT, with 10 psi more or less
pressure in the tires?

Sorry. No data, clue, or experience. I can only estimate the effect.
What might be useful is recording the times and tire pressures of all
the bicycles that cross the finish line after a race and see if there
is any correlation. However, due to the measurement errors and
uncontrolled conditions, the results will probably be meaningless.

Meaningless? I am amazed sir. Amazed! Any set of number can be used to
prove something, and in many cases both the pro and con sides of the
question. I am a great believer in the Mark Twain quote:

"Figures often beguile me, particularly when I have the arranging of
them myself".
--
cheers,

John B.

On Fri, 2 Sep 2016 23:46:35 -0400, Frank Krygowski
wrote:

On 9/1/2016 12:17 PM, Tim McNamara wrote:


Well, putting the screw back in was easy. I popped the plastic bezel
off, reset the pointer to rest against the stop, put the bezel back on
and tried pumping up a tire. The pump seems to work fine and to read
fairly accurately. 105 PSI on the Silca gauge corresponded to 102 PSI
on another hand-held gauge that I have. Of course I don't know the
absolute calibration of either and those two gauges have never perfectly
matched anyway; about the same as this.

A few years ago, I used a laboratory dead weight pressure tester to
check the calibration on my collection of tire pressure gauges. To my
surprise, the most accurate were the pencil-style gages, the ones based
on a simple coil spring and piston. My floor pump (an ancient metal
Nashbar model with bourdon tube gage) was off by 7 psi, reading 100 psi
at a true 93 psi. A pocket sized Zefal gage with a dial was off by
nearly as much.

It is possible to calibrate bourdon tube gages, but I just used a magic
marker to write "Add 7 psi" on the side of the pump. Really, even a 7
percent discrepancy makes little difference when riding.

If the 7 psi was constant over the gauge's range than you did
calibrate it :-)
--
cheers,

John B.

"John B." wrote in message news [snip]
But having said that, snake bite flats aside, what is the actual
importance of tire pressure? What will be the actual (not calculated)
difference in time for a, say 10 mile TT, with 10 psi more or less
pressure in the tires?

Too many variables to isolate the effect by simply comparing times. From experience I have tried various pressures in my Vittoria Corsa slicks and settled on 125psi front and back for most of our local courses. I must admit this is more by feel than measurement.

I started from the premise that on a smooth surface rolling resistance falls with increasing pressure but on a real surface it goes through a minimum as pressure increases. The reason cited for the apparent increase in rolling resistance beyond the minimum being the increased vertical travel of the bike as it starts to lift off over the surface imperfections rarther than them being absorbed by the tyre. As the energy required to lift the bike has to come from your pedalling effort and is lost to propelling the bike forward you travel slower. You can certainly feel the increase in vibration through the aero bar pads on a particular course ridden at different pressures.

After one course "suffered" from a chip seal treatment times were definitely slower. A number of riders including myself tried dropping our tyre pressures and the general concensus was that we got some of our lost time back but difficult to quantify due to changes in temperature, atmospheric pressure and wind speed and direction between races. The bike certainly felt better on that course with around 10psi less in the tyres.

Graham.

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On Sat, 03 Sep 2016 12:49:19 +0700, John B.
wrote:

Meaningless?

Yep. 96.72% of all figures are meaningless (or contrived for the
occasion).

I am amazed sir. Amazed! Any set of number can be used to
prove something, and in many cases both the pro and con sides of the
question.

Way back in High Skool, I was on the forensics (debating) team. As
part of the exercise, we were assigned some manner of debatable issue.
Which side of the issue was selected at random. We were expected to
effectively debate both sides on any argument. During my research, I
would accumulate as many numbers as I thought necessary. It didn't
matter much what the numbers showed, as I could massage my favored
conclusions to fit almost any data.

I am a great believer in the Mark Twain quote:
"Figures often beguile me, particularly when I have the arranging of
them myself".

I know people who prefer to judge by the source instead of by the
validity of the argument. That's much easier than applying the
necessary logic or taking the time to think.
"Trust me" (Jimmy Carter).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 03 Sep 2016 14:22:17 -0700, Jeff Liebermann
wrote:

On Sat, 03 Sep 2016 12:49:19 +0700, John B.
wrote:

Meaningless?

Yep. 96.72% of all figures are meaningless (or contrived for the
occasion).

I am amazed sir. Amazed! Any set of number can be used to
prove something, and in many cases both the pro and con sides of the
question.

Way back in High Skool, I was on the forensics (debating) team. As
part of the exercise, we were assigned some manner of debatable issue.
Which side of the issue was selected at random. We were expected to
effectively debate both sides on any argument. During my research, I
would accumulate as many numbers as I thought necessary. It didn't
matter much what the numbers showed, as I could massage my favored
conclusions to fit almost any data.


Years ago I discovered that a one inch thick pile of (preferably green
and white striped) fan-fold computer paper covered with numbers could
be used as evidence of almost anything :-)

I am a great believer in the Mark Twain quote:
"Figures often beguile me, particularly when I have the arranging of
them myself".

I know people who prefer to judge by the source instead of by the
validity of the argument. That's much easier than applying the
necessary logic or taking the time to think.
"Trust me" (Jimmy Carter).
--
cheers,

John B.

On Sun, 04 Sep 2016 11:46:50 +0700, John B.
wrote:

Years ago I discovered that a one inch thick pile of (preferably green
and white striped) fan-fold computer paper covered with numbers could
be used as evidence of almost anything :-)

Preponderance of evidence, also known as weight of evidence, only
works in civil trials. In criminal cases, the decision of the jury
has to be unanimous.
http://dictionary.law.com/default.aspx?selected=1586
I believe that's also where the "scales of justice" originated.
https://www.google.com/search?q=scales+of+justice&tbm=isch
Modern justice is dispensed by the dollar, not by the pound.

Locally, the courts now require that all court documents be submitted
electronically, thus reducing the paper problem. I'm not sure of the
effect, but the local stationary stores haven't sold green bar paper
in many years. I guess justice will now be dispensed by the megabyte
(and the dollar).


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Sep 2016 09:45:44 -0700, Jeff Liebermann
wrote:

On Sun, 04 Sep 2016 11:46:50 +0700, John B.
wrote:

Years ago I discovered that a one inch thick pile of (preferably green
and white striped) fan-fold computer paper covered with numbers could
be used as evidence of almost anything :-)

Preponderance of evidence, also known as weight of evidence, only
works in civil trials. In criminal cases, the decision of the jury
has to be unanimous.
http://dictionary.law.com/default.aspx?selected=1586
I believe that's also where the "scales of justice" originated.
https://www.google.com/search?q=scales+of+justice&tbm=isch
Modern justice is dispensed by the dollar, not by the pound.

Locally, the courts now require that all court documents be submitted
electronically, thus reducing the paper problem. I'm not sure of the
effect, but the local stationary stores haven't sold green bar paper
in many years. I guess justice will now be dispensed by the megabyte
(and the dollar).

Regarding civil law, I once read a science fiction story about some
distant planet where civil cases were extremely rare. It seems that
the inhabitants of the planet wee a bit on the "wild side" and when
the judge announced his findings in a case the spectators at the trial
leaped from their seats and literally tore the losing attorney apart.

I'm not sure whether that is applicably on all cases but it does seem
appropriate in some :-)
--
cheers,

John B.