Author Topic: TPMS accuracy.....yes, I know but....  (Read 3397 times)

Offline rcannon409

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TPMS accuracy.....yes, I know but....
« on: June 24, 2012, 03:40:40 pm »
Mine has been 4lbs off (low) compared to  my good gauges.  No big deal at all since I use the gauge for accuracy and the tpms for a emergency.

So, I was very bored today.  Not bored enough to change the air in my tires as my ocd neighbor does.  He does this once a month in his 2009 Toyota Tundra.    I bet even ZG does not do this.....

I decided since I have a free supply of Nitrogen, I would fill them with this.  Anyway, I put the bike on the centerstand, and let the air out by removing the valve core. I put new valve cores in as I am just ocd enough to care about this.  Nothign else was done to the tire or wheel.

I filled them with 45lbs of Nitrogen, then dropped it down to 42 with the accurate gauge.  As soon as the tpms registered leavign the driveway, it was dead on at 42 and has stayed accurate during 3 short rides this afternoon.

Is it possible these things can calibrate themselves?  Maybe most of the moisture being out of the tire changed somethign?  I'd be interested to knwo what the hell happened.


Offline jamiemac

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Re: TPMS accuracy.....yes, I know but....
« Reply #1 on: June 24, 2012, 05:20:01 pm »
Nitrogen is inert, & doesn't expand in the heat as much as straight air does. My only explanation.
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Offline lt1

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Re: TPMS accuracy.....yes, I know but....
« Reply #2 on: June 24, 2012, 05:54:40 pm »
As best as I can determine, the TPMS "inaccuracy" is primarily due to owners ignoring ambient temp factors.  Moisture in the tires will also affect the sensors  readings, and possibly elevation changes may affect the readings as well. 
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Offline B.D.F.

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Re: TPMS accuracy.....yes, I know but....
« Reply #3 on: June 24, 2012, 06:12:00 pm »
Yeah, kinda' what Clyde said- the temperature at the time you filled the tires and when you first rode the bike (to turn the sensors on) was probably just in a place where they coincide.

There is nothing on the data sheet of the control device that would indicate it is self calibrating.

There should be no difference in pressure readings of any gas, even mixed ones such as 'air'. 42 PSI is the same regardless of the gas compressed to that pressure. Besides that, you are simply comparing two different pressure reading devices and I cannot think of any difference or property of any gas that could cause them to diverge. ??

Brian

Mine has been 4lbs off (low) compared to  my good gauges.  No big deal at all since I use the gauge for accuracy and the tpms for a emergency.

So, I was very bored today.  Not bored enough to change the air in my tires as my ocd neighbor does.  He does this once a month in his 2009 Toyota Tundra.    I bet even ZG does not do this.....

I decided since I have a free supply of Nitrogen, I would fill them with this.  Anyway, I put the bike on the centerstand, and let the air out by removing the valve core. I put new valve cores in as I am just ocd enough to care about this.  Nothign else was done to the tire or wheel.

I filled them with 45lbs of Nitrogen, then dropped it down to 42 with the accurate gauge.  As soon as the tpms registered leavign the driveway, it was dead on at 42 and has stayed accurate during 3 short rides this afternoon.

Is it possible these things can calibrate themselves?  Maybe most of the moisture being out of the tire changed somethign?  I'd be interested to knwo what the hell happened.
Homo Sapiens Sapiens and just a tad of Neanderthal but it usually does not show....  My Private mail is blocked; it is not you, it is me, just like that dating partner said all those years ago. Please send an e-mail if you want to contact me privately.

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Offline jjsC6

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Re: TPMS accuracy.....yes, I know but....
« Reply #4 on: June 24, 2012, 07:32:54 pm »
I agree on the temperature issue.  I think Kawasaki did us a disservice by having them temperature compensated because it confuses the hell out of figuring out whether to fill them by a gauge, or by what the readout on the bike says when we are riding.
Jim
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Offline rcannon409

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Re: TPMS accuracy.....yes, I know but....
« Reply #5 on: June 24, 2012, 09:21:01 pm »
Great points on the temperature issue. It was at least 95 degrees in my garage and the tires were nto in the shade. No idea how warm they were, but it woudl have been very hot!

Offline B.D.F.

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Re: TPMS accuracy.....yes, I know but....
« Reply #6 on: June 24, 2012, 09:36:10 pm »
The 'rule of thumb' is that you change the tire pressure about 1 1/2 PSI for each 10 F of temp. change. 95 F is about 25 F above the 'standard' temperature (usually 68 F) so the TPS sensors would drop the displayed pressure about 5 PSI at those temps. The on- board sensors are not really full temp. compensated though so they probably read 2 or 3 PSI higher at 95 F than they would at 68 F. Because of that error, the whole idea of temperature compensation becomes confusing.

I use that general rule to inflate tires based on the starting cold temp.. So far it seems to have worked out OK but who could know if the pressures are really ideal or not?

Here is an inflation vs. temp. chart I found: http://www.rvcruzer.com/smartire.php
I have no idea if it is accurate or not but it seems OK.

Brian

Great points on the temperature issue. It was at least 95 degrees in my garage and the tires were nto in the shade. No idea how warm they were, but it woudl have been very hot!
Homo Sapiens Sapiens and just a tad of Neanderthal but it usually does not show....  My Private mail is blocked; it is not you, it is me, just like that dating partner said all those years ago. Please send an e-mail if you want to contact me privately.

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Offline rcannon409

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Re: TPMS accuracy.....yes, I know but....
« Reply #7 on: June 25, 2012, 06:24:30 am »
Brian, the temp figures you gave (68/100) are just about the exact temps I was dealing with, and makes sense.    I imagine they build tps sensors to not be sensitive or the first time a tire showed 45 psi, from being hot, people would start letting air out. 


Offline B.D.F.

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Re: TPMS accuracy.....yes, I know but....
« Reply #8 on: June 25, 2012, 10:20:46 am »
That is why the sensors are temp. compensated in the first place- can you imagine having someone riding a C-14 on a hot day and watching the pressures climb up and up until they reached a scary reading? Quite a few people would stop the bike and let some pressure out and of course when the tires cooled down they would be seriously underinflated. The mfg. would have a deluge of nasty phone calls about the 'defective' tires, wheels, sensors, etc. and nobody would be happy.

The reason we don't normally see the pressure in any vehicle's tires increase is because we cannot read the pressure while they are rolling down the road. Now that we can a lot of people (including me I think) would be put off watching the pressure ride 10, 15, maybe 20 PSI.

Brian

Brian, the temp figures you gave (68/100) are just about the exact temps I was dealing with, and makes sense.    I imagine they build tps sensors to not be sensitive or the first time a tire showed 45 psi, from being hot, people would start letting air out.
Homo Sapiens Sapiens and just a tad of Neanderthal but it usually does not show....  My Private mail is blocked; it is not you, it is me, just like that dating partner said all those years ago. Please send an e-mail if you want to contact me privately.

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Offline Necron99

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Re: TPMS accuracy.....yes, I know but....
« Reply #9 on: June 25, 2012, 02:42:05 pm »
I only use the 78% nitrogen mix... nothing else will do.

BTW, if you were serious about it, you'd call it CDO, not OCD.
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