Are tyre pump pressure gauges accurate or not?

For the past three years I've been using a foot-operated car tyre pump
to inflate my unicycle tyres, which has a built-in gauge reading up to
100psi and only does schraeder valves. Recently my sister bought a
track/floor pump that looks just like the plungers that set off
explosives in cartoons and has two holes, one for schraeder and one for
presta. That too has a gauge, reading up to 160psi.

After feeling a bit tired after a muni ride I decided to check the
pressure, which I normally set at 20psi. I decided to try out the track
pump and it told me the pressure had dropped to 10psi, so I effortlessly
reinflated it to 20psi.

Or so I thought.

Pinching the tyre seemed to be pretty hard and it didn't want to bounce
anymore. So I checked the pressure with a second opinion from the car
pump. It reckoned the tyre was now about 30psi! So my moving the clip I
took it down so the car pump reckoned it was 20psi again. Sure enough,
reclamping the track pump on; it's gauge read just 10psi again.

It was also time to reinflate the 29er Big Apple tyre. The car pump
showed it had dropped to 30psi over the weeks, so I pumped it up to
45psi. Again I swapped it for the track pump... which reckoned it was
30psi.

I swapped the pumps around twice more to confirm that the brief air
escaping from clamping and unclamping the pumps from/to the valves was
not the cause of this relative error. The track pump still gave lower
readings.

Two more tyres to try. My hardly-used freestyle has a Maxxis Hookworm
tyre that can hold an incredible 110psi. Using the track pump is easier
to inflate this one, I took it to 80psi. The car pump reckons it's
90psi.

And my giraffe tyre lost a lot of pressure over the months, down to
30psi on the car pump, or 20psi on the track pump. Using the track pump
I took it up to 60psi, and the car pump reckons it's 65psi.


I'm still experimenting with various tyre pressures with the Big Apple
tyre, and am still confused about which psi my ideal muni tyre pressure
should be. The fact that I now have two pumps reading different
pressures has thrown a spanner in the works.

Has anyone else had more than one pump apparently reading different
pressures? If so, why is this happening?


--
gkmac

"It's a marvellous thing to see, someone in full flight on the
unicycle." - Stuart Maconie, Radio 2
"Oh no! Both my toes have gone numb!" - Joe Hodges
"You also met me gk! I was the one eating the sandwich!" - Adam Gayne
"Act your tyre pressure, not your age." - rob.northcott
------------------------------------------------------------------------
gkmac's Profile: http://www.unicyclist.com/profile/4577
View this thread: http://www.unicyclist.com/thread/53774

I'd say NOT. When we were visiting relatives I had a flat and used their
hand pump to fill my tire, and I went by the gauge on the side instead
of my normal squeze method. Got it up to what the gauge said was about
30 PSI and the tire EXPLODED with a huge bang.


--
forrestunifreak

If I had a signature, it would look something like this.
*'My gallery-NAUCC 2006!'
(http://tinyurl.com/bbf9x)*
BANANA'S FOR JESUS!
_____________________________________________
-last edited by skrobo : today at 11:41 am.-
------------------------------------------------------------------------
forrestunifreak's Profile: http://www.unicyclist.com/profile/6828
View this thread: http://www.unicyclist.com/thread/53774

Consider how much you paid for the two pumps in your example. Even if
they were good quality pumps, most of the cost goes toward making a
good pump, not necessarily a good gauge.

Tire pump gauges are probably only in the right ballpark if you pump
some air into the tire first, pressurizing the pump to equalize what's
in the tire.

My experience is that tire pressure gauges are for entertainment
purposes only. At least the ones on pumps. Some work great, but others
may be way off. Once upon a time I bought an electronic tire gauge from
Performance Bike. It seems to work very well, even though it might be 20
years old now and still on the original battery. But I've never tested
it to see if it's right...

For bikes & unicycles, pinching with the fingers and riding the wheel
seem to be the best ways to assure you have the desired pressure. I
don't consider a gauge necessary for those. For a car however, this
doesn't really work and having the wrong pressure can be bad for the
tires, and bad for fuel economy. My recommendation there is to get a
standalone gauge for cars, and not necessarily one that ranges up to
100 psi, as it will make the "normal car range" a small part of the
scale.


--
johnfoss

John Foss
"jfoss" at "unicycling.com" -- www.unicycling.com
-----------------------------------------------

"The worst thing you can do on a unicycle when you land is stop dead."
-- Kris Holm, world's expert on high-consequence unicycling
------------------------------------------------------------------------
johnfoss's Profile: http://www.unicyclist.com/profile/832
View this thread: http://www.unicyclist.com/thread/53774

I'd suggest that the gauge on the track pump, if it's a decent quality
one, is likely to be far more accurate than the car pump one. Some of
them are actually very accurate (but like John suggested, while you're
pumping the tyre up, not just as a "stick it on and measure the
pressure" gauge).

Rob


--
rob.northcott

'Dartmoor Muni Weekend'
(http://www.unicyclist.com/forums/showthread.php?t=46116) - Last
weekend in May 2006
Same again next year anyone? It'll be dry, I promise.
------------------------------------------------------------------------
rob.northcott's Profile: http://www.unicyclist.com/profile/7436
View this thread: http://www.unicyclist.com/thread/53774

Mine isn't very accurate. It just says 0 all the time. Or at least I
think that's what it reads, it's very difficult to see.


--
cathwood

Cathy

http://www.chuckingandtwirling.co.uk
------------------------------------------------------------------------
cathwood's Profile: http://www.unicyclist.com/profile/9425
View this thread: http://www.unicyclist.com/thread/53774

It is nice to see what pressure your tyre is at, it quickens up the
process of pumping it up. It allows you to know where its most
comfortable to pump it up to for your riding.

As for your prediciment (sp?) I would have to say the only thing I can
think of (except the 'just go with how it feels' method) would be to
buy a tyre pressure gauge. Just one you slip on the valve, more
complicated than a nice pump gauge, but could be a solution. Plus it
will be made to read the pressure (not just an 'add-on') so it *should*
read it accuratly.

mike


--
swarbrim

Add me at

'i like things big' - Amanda

'ive got a pen in my ear, it feels funny' - Dustin Schaap
------------------------------------------------------------------------
swarbrim's Profile: http://www.unicyclist.com/profile/11005
View this thread: http://www.unicyclist.com/thread/53774

i just pump mine for a bit. ride bout 50 meters, bounce a bit n if it
feel gd than WhAYYY gd tire pressure


--
pkplonker

UNICYCLE pwnt!
------------------------------------------------------------------------
pkplonker's Profile: http://www.unicyclist.com/profile/13484
View this thread: http://www.unicyclist.com/thread/53774

I never trust the guage of a bike pump to give me an accurate reading.
Guages on car tire pumps at gas stations are espesially horrable known
to be off by as much as 15psi. I know this becuase I have access to a
300$ digital tire guage used to get the pressure on the tires of rally
cars to the exact desired pressure for the stage up to .001 psi. auto
parts store will sell cheaper versions of this which give the same
results, they look like a big dial indicator with a female presta end
with a pressure release button and ussually cose 15-20$. You pump the
tire up more than you want then stick the guage on, and push the
pressure release valve to get it down to what you think you want.

this probably sounds like over kill for most people (and is), but for
trials i like to use different psi for different lines and it's nice to
know exactly what i'm working with.


--
onetrack

"People over here have a dangerous habit of adding quotes to signature
lines."
-Klaas Bil

I pulled a sick trey varial hickflip over an 8 set yesterday, but
unfortunately it was supposed to be seat in to seat out. I've named it
the dioflip
------------------------------------------------------------------------
onetrack's Profile: http://www.unicyclist.com/profile/6374
View this thread: http://www.unicyclist.com/thread/53774

johnfoss wrote:
Once upon a time I bought an electronic tire gauge from Performance
Bike. It seems to work very well, even though it might be 20 years old
now and still on the original battery. But I've never tested it to see
if it's right...




now thats quality!



I know my gauge isnt accurte


--
dan de man

\"underestimate zombies and you get eaten\"
i got post 77000&99000 in 'm'
(http://www.unicyclist.com/forums/showthread.php?t=27264)'r'
(http://tinyurl.com/m6hs6)
'.' (http://tinyurl.com/gsfgg)'.' (http://postsecret.blogspot.com/)'.'
(http://tinyurl.com/f7bag)
-_chug_counterfeit_tobasco_sauce_while_holding_b ananas_and_riding_on_goats_for_christ_-
pm me to rent a . any site you want (nothing rude though)
tomtrevor wrote:
Im gunna punch you in the face with a ski boot
------------------------------------------------------------------------
dan de man's Profile: http://www.unicyclist.com/profile/11403
View this thread: http://www.unicyclist.com/thread/53774