On Wed, 30 Jan 2008 16:34:34 -0600, Ben C <
[email protected]> wrote:
>On 2008-01-30, [email protected] <[email protected]> wrote:
>> On Wed, 30 Jan 2008 12:44:26 -0800, "Tom Nakashima"
>><[email protected]> wrote:
>>
>>>
>>><[email protected]> wrote in message
>>>news:[email protected]...
>>>> 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=ZBBiAAAAEBAJ&pg=PP1&dq=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_pressure_monitoring_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 pressure:
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.bicycles.tech/msg/37a21cdb51dfd50c
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=5cJLAAAAEBAJ&pg=PP1&dq=599790
A less savage wire-bail version of a "PXJWCTTRKE-GKUABD FOE PNEUMATIC
TIEES":
http://www.google.com/patents?id=2NdRAAAAEBAJ&pg=PA29&dq=979699
What I really need is one of these:
http://www.google.com/patents?id=YVM_AAAAEBAJ&pg=PP1&dq=644380
http://www.google.com/patents?id=5cJLAAAAEBAJ&pg=PP1&dq=599790
http://www.google.com/patents?id=E81fAAAAEBAJ&pg=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/archiv...A123BEE33A2575AC2A9619C94679ED7CF&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
