Your thumb is probably more accurate

I actually rely on my thumb to check tire pressure when I repair a flat on
the road, since I don't carry a mechanical pressure gauge when I ride. My
thumb gauging technique is accurate enough.

I find my thumb virtually useless for checking tire pressure, especially
after laboring a while to inflate one on the road. The problem is that
anything over 80psi or so feels "hard." What I find works much better,
assuming both front & rear tires are the same type & width, is to "ping" the
tire and see if they both sound the same. Or, but a bit less accurate,
"calibrate" my thumb by seeing how the other (presumably correctly inflated)
tire feels, then checking the one just inflated.

But thumb alone, without a reference point, just doesn't work for me.
Especially after having just inflated a tire. I'll always think it's got
more air than it actually does. Wishful thinking, no doubt, adds to it.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


"Tom Nakashima" wrote in message
...

wrote in message
...

These tests need to be viewed in context. First comes inflation with
pump having and easily readable and accurate gauge. Then comes the
ride on which that pressure is assessed. The next day, assuming a
reasonable inner tube is used, the tire should again be ridable unless
there is a leak. A thumb or bounce test will reveal whether one of
the tires got a leak on last use, not the precise pressure... that
doesn't matter anyway.
Jobst Brandt

I actually rely on my thumb to check tire pressure when I repair a flat on
the road, since I don't carry a mechanical pressure gauge when I ride. My
thumb gauging technique is accurate enough.

We ran a recent test on the road when I had flattened on my rear tire.
One of the riders had a tire pressure gauge. I told him I didn't need
one, I use my thumb. He said; "Let's see how accurate you are?" After I
repaired and pumped up the flatten tube/tire, I used my thumb to feel the
"non-flatten front" tire, then thumbed my rear tire and felt I was a
little low. I pumped it up a little more until the rear tire pressure
felt like the front tire pressure, by using my thumb as a gauge. We then
put the mechanical tire pressure gauge to both tires and they were within
a pound of eachother.
-tom

Results? I was surprised to find that all the pencil gages were much
better than the dials. At true 30, they read 31, 31 and 32. The
Zefal read 39, and the Nashbar read 36. At 90.5 true psi, the Nashbar
read 95.

Last time we did a check on pressure gauges on pumps, we found them to be
far more accurate at the higher end of the scale (80-130psi) than at the
lower end. And, interestingly, it seemed like they were the furthest-off
right around 30psi. We haven't done this experiment for quite some time
though, so I don't really know if current gauges are better or worse than
before.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


wrote in message
...
On Jan 30, 5:44 pm, wrote:


These tests need to be viewed in context. First comes inflation with
pump having and easily readable and accurate gauge. Then comes the
ride on which that pressure is assessed. The next day, assuming a
reasonable inner tube is used, the tire should again be ridable unless
there is a leak. A thumb or bounce test will reveal whether one of
the tires got a leak on last use, not the precise pressure... that
doesn't matter anyway.

Riding the bicycle on successive days without topping off pressure
will reveal what a 85psi tire does in comparison to a 100psi one.
That it was 85psi will be revealed when topping off a tire that was at
the lower end of acceptable pressure. Again, the pump has a gauge.

Cutting all this a laboratory analysis is misplaced as I see it. I'm
only being practical with my daily ride. The sound of the bounce
tells me whether I need more precise scrutiny. It doesn't tell me
what the pressure is unless it is "hard".

Regarding accuracy: I recently used a dead weight pressure gage
calibrator to test three pencil-style gages, one plastic Zefal dial-
type gage (presta & shraeder head), and the dial-type gage built into
my floor pump (Nashbar brand). The pencil gages varied in
construction, from nice heavy-feeling metal to flimsy-feeling plastic.

Unfortunately, I was able to test only the floor pump at 90 true psi.
All gages were tested at 30 true psi.

Results? I was surprised to find that all the pencil gages were much
better than the dials. At true 30, they read 31, 31 and 32. The
Zefal read 39, and the Nashbar read 36. At 90.5 true psi, the Nashbar
read 95.

I assume the Nashbar is a true bourdon tube gage. If so, it's pretty
easy to calibrate - but it's easier to just remember to add about 5
extra psi. The Zefal is a disappointment, and it's not obvious how to
take it apart to improve it.

Second point: Of course, "when topping off" a tire, the unpressurized
volume in the pump normally reduces the tire's pressure. A gage on a
floor pump like mine gives an initial reading lower than what the tire
actually was.

- Frank Krygowski

"Mike Jacoubowsky" wrote in message
...
I actually rely on my thumb to check tire pressure when I repair a flat
on
the road, since I don't carry a mechanical pressure gauge when I ride.
My thumb gauging technique is accurate enough.

I find my thumb virtually useless for checking tire pressure, especially
after laboring a while to inflate one on the road. The problem is that
anything over 80psi or so feels "hard." What I find works much better,
assuming both front & rear tires are the same type & width, is to "ping"
the tire and see if they both sound the same. Or, but a bit less accurate,
"calibrate" my thumb by seeing how the other (presumably correctly
inflated) tire feels, then checking the one just inflated.

May I ask, how do you "ping" the tire?
I think I would use the bounce test over "pinging" a tire, unless you have
a good method for "pinging".



But thumb alone, without a reference point, just doesn't work for me.
Especially after having just inflated a tire. I'll always think it's got
more air than it actually does. Wishful thinking, no doubt, adds to it.

Your reference is your other tire when thumb gauging for pressure,
unless both tires are flat.


--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


"Tom Nakashima" wrote in message
...

wrote in message
...

These tests need to be viewed in context. First comes inflation with
pump having and easily readable and accurate gauge. Then comes the
ride on which that pressure is assessed. The next day, assuming a
reasonable inner tube is used, the tire should again be ridable unless
there is a leak. A thumb or bounce test will reveal whether one of
the tires got a leak on last use, not the precise pressure... that
doesn't matter anyway.
Jobst Brandt

I actually rely on my thumb to check tire pressure when I repair a flat
on
the road, since I don't carry a mechanical pressure gauge when I ride.
My thumb gauging technique is accurate enough.

We ran a recent test on the road when I had flattened on my rear tire.
One of the riders had a tire pressure gauge. I told him I didn't need
one, I use my thumb. He said; "Let's see how accurate you are?" After I
repaired and pumped up the flatten tube/tire, I used my thumb to feel the
"non-flatten front" tire, then thumbed my rear tire and felt I was a
little low. I pumped it up a little more until the rear tire pressure
felt like the front tire pressure, by using my thumb as a gauge. We then
put the mechanical tire pressure gauge to both tires and they were within
a pound of eachother.
-tom

On Wed, 30 Jan 2008 16:34:34 -0600, Ben C wrote:

On 2008-01-30, wrote:
On Wed, 30 Jan 2008 12:44:26 -0800, "Tom Nakashima"
wrote:


wrote in message
...
The basic idea of this spring-loaded tire pressure gauge is okay, but
the scale is a bit off.

You'd need a dial indicator micrometer to measure the change in tire
compression with the spring and plunger head shown:

http://www.google.com/patents?id=ZBB...660445#PPP1,M1

Cheers,

Carl Fogel

Looks like it does have a built-in indicator.
I'm afraid a dial indicator wouldn't work well, unless you're on top-dead-
center of the radius. If you had a micrometer, you wouldn't need the spring
plunger head shown.
And glad you're finally convinced about using your thumb as a gauge...
for awhile there thought you were calling us a liar. ;-)
JB's bounce method also works well.
-tom

Dear Tom,

I'm not convinced that a thumb is all that accurate, despite
anecdotes, but I think that it would be better than that contraption.

The bounce test sounds even less accurate.

Another pressure test you have mentioned before is to use a
3-decimal-place odometer to measure apparent mileage over exactly the
same route.

Someone has since explained to me that that's how some cars with
low-tyre-pressure warning lights do it. You have an individual odometer
on each wheel and look for discrepancies, averaged out over reasonable
mileages to filter out the effects of steering.

http://en.wikipedia.org/wiki/Tire_pr...itoring_system

I made some estimates for how 15 miles would look on the odometer
against percentage tyre drop:

0% 15.000
1% 15.006
2% 15.011
3% 15.017
4% 15.022
5% 15.028
6% 15.033
7% 15.039
8% 15.045
9% 15.050
10% 15.056
11% 15.061
12% 15.067
13% 15.073
14% 15.078
15% 15.084
16% 15.089
17% 15.095
18% 15.101
19% 15.106
20% 15.112
21% 15.118
22% 15.123
23% 15.129
24% 15.135
25% 15.140

Dear Ben,

For fun, I eased my 110 psi front tire down to 100 psi for today's
ride.

With my current ~25 mm 700c (allegedly 28 mm), my daily ride increased
from 15.043 yesterday at ~110 psi to 15.062 miles at ~100 psi, about
1.25% more "miles" for about 9% less air pressure.

(The softer the tire, the greater the "shortcut" that it takes through
the enlarged contact patch, which means an effectively smaller tire,
which means more tire spins over the same distance, which produces a
larger "mileage" figure.)

A single spin of the tire (about 7 feet) is just over 0.001 miles
(5.28 feet), so I always start with my cyclocomputer magnet just past
the sensor from the same crack in my driveway and finish at the same
spot. Otherwise, my figures would be less accurate and the heavens
might fall.

The test was conducted under the watchful eye of this obstruction:
http://i30.tinypic.com/i4o6fc.jpg
http://i25.tinypic.com/142svhe.jpg

Alas, it wasn't quite watchful enough to warn me about a goathead
somewhere ahead on the path. About a mile from home, my rear tire
announced my third flat of the year, having gone soft enough to feel
odd in a corner.

Rather than stop and fix the flat in the cold, I slowed down, leaned
over the handlebar, and limped home.

Here's a thumb-test showing the rear tire's pressu
http://i29.tinypic.com/aaj1ip.jpg

When I pulled the tube, it was oddly dirty--the soft tire had flexed
enough to let dirt inside in only a mile on pavement after last
night's snow had melted.

Ryan Cousineau may have suffered a worse fate under similar
circumstances:
http://groups.google.com/group/rec.b...a21cdb51dfd50c

Ryan's dirt clod may have been just sediment from muddy water that got
into his cross rim, but it could be that his tire pressure was low
enough to let dirt in past the clincher rim. (I didn't go through any
water after the tire began to go soft, so mine was just road dirt.

I couldn't feel anything inside the tire, but I stopped falling for
that that false reassurance years ago. Peering myopically at the tire
inch by inch soon revealed the culprit:
http://i30.tinypic.com/11uc1sy.jpg

The base of the goathead thorn is the little white dot at 4 o'clock
from the valve stem nut on the tire. Couldn't feel it on the inside of
the tire, but it matched up with the hole in the tube.

Here's the thorn extracted:
http://i27.tinypic.com/2nhgp51.jpg

The hole is at 4 o'clock to the thorn, well off the centerline of the
tread.

Thorn-catchers are often recommended, but may not work too well. This
one has the most ferocious design that I've seen--look at the teeth:
http://www.google.com/patents?id=5cJ...=PP1&dq=599790

A less savage wire-bail version of a "PXJWCTTRKE-GKUABD FOE PNEUMATIC
TIEES":
http://www.google.com/patents?id=2Nd...PA29&dq=979699

What I really need is one of these:
http://www.google.com/patents?id=YVM...=PP1&dq=644380
http://www.google.com/patents?id=5cJ...=PP1&dq=599790
http://www.google.com/patents?id=E81...=PP1&dq=608839

But no one seems to make them any more. I can't even find them used on
eBay.

But things could be worse:

"Bits of broken glass were found on the Merrick Road on Long Island
last season in quantities sufficient to arouse suspicion in the minds
of the wheelmen who ride daily over that sandpapered highway. Since
the law against strewing glass, tacks, &c. in the public streets went
into effect in this State, there have apparently been few, if any,
willful violations until last Sunday, when a number of tires were so
badly punctured as to destroy their usefulness. Several Brooklyn
cyclists were the sufferers. They encountered the glass between the
Valley Stream and Springfield. It is understood that the hotel keepers
in that vicinity, they being benefited the most by the touring
wheelmen, will organize at once to prevent a repetition of the glass
strewing, as well as to punish the offenders."
--NYT, July 29, 1896

http://query.nytimes.com/mem/archive...CF&oref=slogin

The New York Times hasn't reported such atrocities recently, so the
glass-strewing miscreants, willful or otherwise, must have been
rounded up and lynched (probably in Springfield by a mob led by Moe
Szyslak).

The article is genuine. During the bike boom, hotels were eager to
attract guests riding bicycles, just as the NYT was eager to cover
bicycling in amazing detail and routinely reminded readers that
applications to join the League of American Wheelmen (which rated
hotels) could be obtained at the newspaper office.

Cheers,

Carl Fogel

Mike Jacoubowsky wrote:
I actually rely on my thumb to check tire pressure when I repair a flat on
the road, since I don't carry a mechanical pressure gauge when I ride. My
thumb gauging technique is accurate enough.

I find my thumb virtually useless for checking tire pressure, especially
after laboring a while to inflate one on the road. The problem is that
anything over 80psi or so feels "hard." What I find works much better,
assuming both front & rear tires are the same type & width, is to "ping" the
tire and see if they both sound the same. Or, but a bit less accurate,
"calibrate" my thumb by seeing how the other (presumably correctly inflated)
tire feels, then checking the one just inflated.

But thumb alone, without a reference point, just doesn't work for me.
Especially after having just inflated a tire. I'll always think it's got
more air than it actually does. Wishful thinking, no doubt, adds to it.

The "thumb test" also works better on tires with thin casing; e.g. a
Maxxis Hookworm [1] feels hard even when under-inflated, since the
casing is so stiff.

[1] http://www.maxxis.com/products/bicycle/product_detail.asp?id=90.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

May I ask, how do you "ping" the tire?
I think I would use the bounce test over "pinging" a tire, unless you have
a good method for "pinging".

Ping, thump, flick it with your finger, whatever. The idea is that a more
highly inflated tire puts more tension on the casing so it sounds different.
Bouncing a tire

However-

I just performed the experiment in a controlled environment, and I'm not
convinced I can reliably judge the pressure much closer using a "ping" test
vs squeezing. As for bouncing a tire, I guess that'll be the next experiment
for someone to try. Does a tire at 90psi bounce significantly differently
than one inflated to 120? By differently, the only thing we can judge is
height, correct? Bounce two wheels from the same height and see if the one
inflated more highly bounces back up a greater amount?

I did the "ping" experiment. Someone else gets to do the bounce and report
back!

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


"Tom Nakashima" wrote in message
...

"Mike Jacoubowsky" wrote in message
...
I actually rely on my thumb to check tire pressure when I repair a flat
on
the road, since I don't carry a mechanical pressure gauge when I ride.
My thumb gauging technique is accurate enough.

I find my thumb virtually useless for checking tire pressure, especially
after laboring a while to inflate one on the road. The problem is that
anything over 80psi or so feels "hard." What I find works much better,
assuming both front & rear tires are the same type & width, is to "ping"
the tire and see if they both sound the same. Or, but a bit less
accurate, "calibrate" my thumb by seeing how the other (presumably
correctly inflated) tire feels, then checking the one just inflated.

May I ask, how do you "ping" the tire?
I think I would use the bounce test over "pinging" a tire, unless you have
a good method for "pinging".



But thumb alone, without a reference point, just doesn't work for me.
Especially after having just inflated a tire. I'll always think it's got
more air than it actually does. Wishful thinking, no doubt, adds to it.

Your reference is your other tire when thumb gauging for pressure,
unless both tires are flat.


--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


"Tom Nakashima" wrote in message
...

wrote in message
...

These tests need to be viewed in context. First comes inflation with
pump having and easily readable and accurate gauge. Then comes the
ride on which that pressure is assessed. The next day, assuming a
reasonable inner tube is used, the tire should again be ridable unless
there is a leak. A thumb or bounce test will reveal whether one of
the tires got a leak on last use, not the precise pressure... that
doesn't matter anyway.
Jobst Brandt

I actually rely on my thumb to check tire pressure when I repair a flat
on
the road, since I don't carry a mechanical pressure gauge when I ride.
My thumb gauging technique is accurate enough.

We ran a recent test on the road when I had flattened on my rear tire.
One of the riders had a tire pressure gauge. I told him I didn't need
one, I use my thumb. He said; "Let's see how accurate you are?" After
I repaired and pumped up the flatten tube/tire, I used my thumb to feel
the "non-flatten front" tire, then thumbed my rear tire and felt I was a
little low. I pumped it up a little more until the rear tire pressure
felt like the front tire pressure, by using my thumb as a gauge. We then
put the mechanical tire pressure gauge to both tires and they were
within a pound of eachother.
-tom

"Mike Jacoubowsky" wrote in message
...
May I ask, how do you "ping" the tire?
I think I would use the bounce test over "pinging" a tire, unless you
have
a good method for "pinging".

Ping, thump, flick it with your finger, whatever. The idea is that a more
highly inflated tire puts more tension on the casing so it sounds
different. Bouncing a tire

However-

I just performed the experiment in a controlled environment, and I'm not
convinced I can reliably judge the pressure much closer using a "ping"
test vs squeezing. As for bouncing a tire, I guess that'll be the next
experiment for someone to try. Does a tire at 90psi bounce significantly
differently than one inflated to 120? By differently, the only thing we
can judge is height, correct? Bounce two wheels from the same height and
see if the one inflated more highly bounces back up a greater amount? I
did the "ping" experiment. Someone else gets to do the bounce and report
back!
--Mike Jacoubowsky


Umm, not sure what you mean by "controlled environment"??
Sound proof room?
Try doing your ping test on a windy day, or in a group of chatting cyclist,
or on a busy city street.
To me, carbon compound, or rubber acts as an "insulator" to sound.
It would be very difficult to determine sound to detect pressure in a tire,
unless you have mechanical instruments to do so.

I personally don't do the bounce test, so I can't help you there.

The thumb test I can see from pictures that their technique is wrong.
Some here are trying to pinch the tire between their index finger and
thumb against the casting or sidewalls.
My method is to put one or two fingers under the rim and press down with my
thumb on top of the tire. Make sure the tire is secure on the ground.
This gives me a good feel of hardness (pressure in the tire)
I use the inflated tire as my gauge, roughly 100 psi.
I thumb-gauge to make the underinflated tire equal by adding air with a
pump.
It's easy to do, not sure what's complicated about all this.
Give it a try Mike, in a non-controlled environment of course.
-tom