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Old 07-21-2014, 04:13 AM   #1
LordSmoke OP
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Tire pressure gauge comparison

Introduction
I purchased a 2014 R1200GSW in April of 2014. Recommended tire pressures for this bike are 36.3psi for the front tire and 42.1psi for the rear.

Given the cost and that this is my first bike with a tire pressure monitoring system, I thought it worthwhile to invest in a good tire pressure gauge. Accuracy information for various gauges proved frustratingly difficult to come by and prices varied greatly. I finally purchased a 2" dial Accu-gage because it was the only one, IIRC, that made reference to an independent accuracy standard, ANSI B40.1.

The gauge arrived, but I still had no idea of the accuracy of this or any other of my gauges. So, I decided to do a comparison of my gauges and the TPC/RDC system on the BMW.

Materials and Methods
Three gauges were tested and shown in the included figure.


These were (left to right):

Accu-gage: 0-60psi. 2" dial. I first noticed the ANSI specification on the website, www.getagauge.com, and as a matter of principal, I should have bought it from them. However, I was ordering a number of items from Amazon, so I just added the gauge to that order for convenience.

Syracuse: 10-50psi. 6" pencil. Purchased sometimes after the breakup of Gondwanaland, this has been rattling around in various toolboxes of mine for years. It was my "go to" gauge. Made in Syracuse, NY, the company appears to have closed its doors in 2008.

Made-in-China: 6-50psi. 3" pencil. I got this from a fish bowl at the checkout counter at Advance Auto. I kept it in the dash pocket of a car that I have since sold, and rediscovered it while tossing out a box of miscellanea from that car that had been sitting in my garage.

The gauges were compared to each other and the TPC/RDC system by first setting the pressure in the front and rear tires using the Accu-gage. The pressure was then read with the 6" pencil gauge and the 3" pencil gauge. The pressure was checked again using all gauges in the order - Accu-gage, 6", 3", and checked a third time. The bike was then ridden down the road enough to get a TPC/RDC reading to which to compare the gauge readings.

Initial pressure was set at 37psi for the front and 43 psi for the back. This is slightly above the recommended 36.3 and 42.1 to allow for air loss during checking.

I didn't record the ambient temperature, but I would guess it to be about 83F. It had been 85-90F during the day, and a thunder storm had just passed that cooled things off. I do recall the temp was definintely above 80F at the time of the test.

Results
The pressure readings are shown in the table below and the included plot. Means and standard deviations for the third set of measurements presented to reduce the effect of systematic pressure reduction with repeated measurements.

FRONT (psi)
Accu 6" 3"
1 37.0 37.0 38
2 37.0 36.5 38
3 36.5 36.0 37 -> mean=36.5, s.d.=0.5

REAR (psi)
Accu 6" 3"
1 43.0 43.0 43
2 42.5 42.0 44
3 42.5 42.0 43 -> mean=42.5, s.d.=0.5

The TPC/RDC readings were about 1.5psi lower than the final, average gauge readings for the front (35 v. 36.5psi) and 2.5psi lower than the final, average gauge readings for the rear (40 v. 42.5psi).

TPC/RDC (psi)
FRONT 35
REAR 40



Discussion
All gauges showed surprisingly close agreement. Maximum difference between any readings was 2.0psi (38-36psi) for the front tire and 1.5psi (44-42.5psi) for the rear. The TPC/RDC reads systematically lower, but its values are algorithmically adjusted to a tempurature of 68F.

Conclusion
I seem to have been worried for naught. Any of my gauges would provide sufficient agreement with the TPC/RDC, assuming it is taken as the gold standard. However, the release button, hose, and 90-degree head on the Accu-gage make its purchase at 21.89USD (plus tax and ~5USD shipping) worthwhile. As per the instructions in the BMW manual, I will probably air the tires to 1-2psi above the nominal value to adjust for the difference in readings between the gauge and TPC/RDC.
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Old 07-21-2014, 08:57 AM   #2
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I have read several comparisons of gauges in magazines and they also reached your conclusion that almost all gauges are accurate enough to use to measure tire pressure. I have also compared the half a dozen gauges that I have collected through the years and found they were also accurate even after many years of use and storage.
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Old 07-21-2014, 03:04 PM   #3
LordSmoke OP
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Yup, it seems the main thing is to get any decent gauge (and most appear to be so) and check the air regularly.
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Old 07-21-2014, 04:55 PM   #4
randyo
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I like the AccuGage for the simple fact it has a pressure release valve

worth it for setting pressure for releasing pressure smoothly and not checking with a stick and finding out you released too much

also easier to get at many valve stems that you can't get a stick on
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Old 07-24-2014, 06:28 PM   #5
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I have the same issue with my first BMW, a K1200 GT. The tire pressures have a decimal ?????
And I was soooo happy checking the pressure in my Guzzi's tires with my foot!!
Oh well it's progress I guess.
To solve the problem I bought this gage ( Fig. 1.0 below ) from Grainger's because it is capable of 1% accuracy. TWO decimal places, and it came with a calibration report traceable to NIST. Then attached it to a filler with bleed off button I had.
Close and consistent enough for me. But I do need to zero it for the changes in atmospheric pressures of our costal weather.
It works a lot better than the on board tire air pressure monitor system that seems to be only 5% accurate 10% of the time.
The BMW system was total crap when I first got the bike and worked rarely. A service bulletin came out that stated the security system transmitter interfered with the TPS and a new PN was available. So, being the accuracy sucker that I am I coughed up the $275 for the new security module. I had also replaced both wheel sensors at $125 each plus charges for the bike to chat with Dur Fuhrer over the internet in order to calibrate the system. Now at least the TPS reads something all the time.
Bottom line, I don't put too much stock in what it reads.
But it will tell you if you have a very low air pressure situation.
Typically I set tire air pressure to the exact BMW requirement out to one decimal because I easily can with this digital gage.
The TPS reads all sorts of pressures and often changes during the ride.
In general the TPS is .7 PSI high for the front and 1.2 PSI low for the rear.
Making and average error of +.15 front and -.35 for the rear.
My bike is an 07 K1200GT and is shown below in Fig. 2.0

Fig. 1.0



Fig. 2.0

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fritzcoinc screwed with this post 07-25-2014 at 09:27 AM
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Old 07-24-2014, 07:12 PM   #6
cameron110
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Thanks for time you took to compare cheap and good gauges, I wouldn't have guessed the results. You may already know this but odds are good some who reads this thread won't so here it goes:


Don't sweat the decimal in the MFG recommended tire pressure they are simply the result of translation from metric (BAR) to SAE (PSI).



In reality there is a range of pressure that is reasonable for your particular bike tire combo. The best number for you falls somewhere in there and is your particular favorite balance between traction and tire longevity. Also a pressure that works great now in the heat of summer might be a bit harder than you want to run in the winter when the temps drop. Making it more complex is that when you change tire model (or the mfg changes compound slightly for your next set) you'll have to figure it out all over again.

The science and wisdom of how much pressure to run is analogous to what weight/brand/type of oil to run. figure out what works for you and go ride.

FWIW The OP's advice to check often it good, I see lots of tires that wear out much faster than they should due to being run too soft.
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Old 07-25-2014, 08:07 AM   #7
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Quote:
Originally Posted by cameron110 View Post
Thanks for time you took to compare cheap and good gauges, I wouldn't have guessed the results. You may already know this but odds are good some who reads this thread won't so here it goes:


Don't sweat the decimal in the MFG recommended tire pressure they are simply the result of translation from metric (BAR) to SAE (PSI).



In reality there is a range of pressure that is reasonable for your particular bike tire combo. The best number for you falls somewhere in there and is your particular favorite balance between traction and tire longevity. Also a pressure that works great now in the heat of summer might be a bit harder than you want to run in the winter when the temps drop. Making it more complex is that when you change tire model (or the mfg changes compound slightly for your next set) you'll have to figure it out all over again.

The science and wisdom of how much pressure to run is analogous to what weight/brand/type of oil to run. figure out what works for you and go ride.

FWIW The OP's advice to check often it good, I see lots of tires that wear out much faster than they should due to being run too soft.
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Old 07-25-2014, 09:24 AM   #8
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Quote:
Originally Posted by randyo View Post
I like the AccuGage for the simple fact it has a pressure release valve

worth it for setting pressure for releasing pressure smoothly and not checking with a stick and finding out you released too much

also easier to get at many valve stems that you can't get a stick on
quite true. I'm a Accu-Gage fan also because it's a good company that stands behind their product with excellent customer support. I mentioned it before, but since they've come up in discussion, I'll toot their horn again:

http://advrider.com/forums/showthrea...ight=accu-gage

I actually just bought a second one, as i got tired of moving it between vehicles and tool box. now there's one for the box and one for the cage.
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Old 07-25-2014, 09:34 AM   #9
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Long ago, when racing, we'd set out pressues so they would raise a couple/three PSI (cold > hot) . . . .

Even the pro teams follwoed that rule of thumb . . . .

Accuracy is good, but less necessary than repeatability, IMO.
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Old 07-25-2014, 09:37 AM   #10
fritzcoinc
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Quote:
Originally Posted by cameron110 View Post

Don't sweat the decimal in the MFG recommended tire pressure they are simply the result of translation from metric (BAR) to SAE (PSI).


FWIW The OP's advice to check often it good, I see lots of tires that wear out much faster than they should due to being run too soft.

Dummkopf!! only Mein Fuhrer knows proper air pressure for a BMW. Und YOU MUST FILL WITH AIR TO DICIMAL point!!!!!!!!! ( click of boot heals )Sieg Heil!!!

Seriously, your correct and +1 on the minimizing of tire wear by careful attention to air pressure.
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Old 07-25-2014, 09:38 AM   #11
fritzcoinc
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Quote:
Originally Posted by bomber60015 View Post
Long ago, when racing, we'd set out pressues so they would raise a couple/three PSI (cold > hot) . . . .

Even the pro teams follwoed that rule of thumb . . . .

Accuracy is good, but less necessary than repeatability, IMO.
+1 as long as the same gage is used and that gage is not adjusted.
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Old 07-25-2014, 12:35 PM   #12
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Tps

I have a 2008 BMW K1200S, and the owner's manual says that the TPS uses an algorhythm (Sp?) so that the PSIs are recalculated to what they would be at 67 deg F. In other words, the PSI reading that shows when the tire is at 95 deg is not the real PSI, it is what it would read if the tire is at 67.

I now ignore my TPS readouts. What bullshit.
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Old 09-24-2014, 12:16 PM   #13
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Ya can learn something new evert day.

Had a flat on the old K1200.
Took the tire to a shop for a patch.
The dude forgot to put my valve cap back on the stem. It was the kind of cap I always use on my bikes, the metal one with the core removal tool made on top.
Patch didn't hold. Stuck at work I jump in the company PU and go get a cheap rope type plug kit. While I'm there I pick up a package of metal valve stem caps with the core removal tool on top.
Plug the tire, it holds air, I get ready to put the new cap on and happen to see a warning on the back of the package " Not for use on TPS systems ".
Sure enough I have a metal cap on the front stem as well.
I change them out to plastic and " fuck me running" the pressure now reads very close to what I set and the system picks up the wheel signal almost instantly with the plastic caps in place.
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Old 09-25-2014, 09:59 AM   #14
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Quote:
Originally Posted by randyo View Post
I like the AccuGage for the simple fact it has a pressure release valve

worth it for setting pressure for releasing pressure smoothly and not checking with a stick and finding out you released too much

also easier to get at many valve stems that you can't get a stick on
Agreed, I have that gauge and really like it. Mine's several years old with weekly use on five vehicles and it still works perfectly.


One time I forgot to release the pressure in the gauge after taking a measurement. When I grabbed the gauge a week later, it was still on the same reading and hadn't leaked down at all.
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Old 09-25-2014, 03:19 PM   #15
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Same conclusion I have come up with . Except to use a gauge with the proper range. Setting a dirt bike tire to 10 psi with a 60 lb gauge does not work , a 20 lb gauge is better .
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