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Tire Pressure Readings - How Accurate?

Glennn

Glennn

Moped
G'day All,

When I check my cold tyres - sorry tires - with a analogue pressure gauge at home I had PSI pressures of about 40(F) and 43(R).

On the road before the tires have warmed up the TPS on the dash shows 37 and 40 respectivly.

This morning I went straight to a petrol station (within a couple of miles) and put air in the tires with a digital machine to 42 and 42. It put air in the front, and dropped a 1 PSI from the rear.

Back on the road the TPS on the dash showed 38 and 41 and then never got higher than 40 and 42.

Thoughts on the TPS accuracy?  What should I be chasing?

I ask because the handling in corners yesterday wasn't what i would call confidence inspiring.  I haven't messed with the suspension yet - and I mean to - but what looks like the lower pressure in the front wheel I feel would have contributed to the handling (bike felt like it wanted to drop in corners)

TIA,

Glenn
 
When your tyres are warm (we speak Commonwealth here too!) compressed air will cool them off a bit and this might well give the results you're seeing.  Most of us keep the pressure at about the same place you do.

And just because the machine at the petrol station was digital, it doesn't mean it's necessarily accurate either.  The same is actually true of your TPS.  Lots of things can affect accuracy and to have something off by a single PSI isn't all that bad.
 
I have noticed the same thing in the last week. I was reading in the owners Manuel not an hour ago. It states that a pressure gauge will not be accurate because of the TPS sensor. I don't know how I feel about that. I am religious about checking the tire pressure.
 
I had to plug my pr3 rear. So I have been monitoring my
pressure. I aired both up to 42 with my compresser .
the dash read 44 on both. I got the rear up to 46 front
45 I think. every time I start with 44 on both. So they
say 2 lbs different than the pencil ( New) pressure
Guage

Chuck 08 concours14 ABS  ???
 
I've found the TPS readings on my 2010 to be very accurate.  I have a high quality calibrated analog pressure gage that I use for autocross car tires, and I use that to set the C14 pressures cold to 40 front, 43 rear.  Out on the road, TPS reads the same numbers.  After warmup, they each go up 1-2 PSI.  I did this cross check several times during the first few months I had the bike since I didn't think TPS would be that good, but I was impressed! 
 
That's exactly what's needed, Tim - a calibrated standard against which to measure.  Thanks for letting us know how it went.
 
Thanks for the replies, Guys.

On the back of Tim's comments I'll see if I can chase 42 42 via the TPS readings, I'm lucky with a servo so close down the road so it isn't too much hassle to try to get dialled in.  I'm not overly anal about tyre pressure, but at the same time I read about people's experiences here with tyre life so I want to try and give myself the best baseline to start from - this is fully acknowledging how crap the stock tyres are too.
 
I use a quality analog gauge for a reference and the TPS typically indicates 2 psi higher than the analog gauge. With my 2010 Camaro the TPS is spot on versus the gauge, this is also the case with our Highlander so my assumption is the Connie's TPS is a bit optimistic. I'm also curious as to how the TPS could affect the reading of an external gauge...
 
Yup..Agreed with Tim

My mechanic use the high quality calibrated pressure gauge...the reading is exactly the same with TPS

My basic pressure gauge or even the one at petrol pump always read higher..So I have pump in more air in order to get my preferred pressure per the TPS
 
Mine were real close. I would set them for 42 PSI cold. Normally when I would start out it would read 42 or 43 on the dash. Basically, they stayed about a pound or less. I do remember a couple of times where it did read two. But mine always read a hair higher than the manual gauge. I never had it read lower.
 
could be different climate  ;)

Now for sure, we all know the TPS give most accurate reading

IMO...every bikes should have this function (TPS)
 
    I somewhat agree. The TPS is one of the features of the C14 that I do like most. In my case, they proved their worth when they warned me of a tire going flat fast in a fast running, twisty section of road. But I also do not like too much unnecessary technology on the bike just for technologies sake. Although I do think the TPS is a worth while system. It has had a good amount of trouble. And it is also fairly pricey to keep working when sensors go bad or the battery life runs out. So in that case, I'm on the fence whether that price (as well as the extra cost of the bike) is really worth it.  And keep in mind, although extended warranties help cover some of this. Extended warranties do cost money as well.  And they do not cover planned sensor life.
      Then the extra weight and complexity comes into play also. So although I do think that the TPS itself is a worth while system (which could save you trouble or worse). It 's complexity of being tied into another system that I personally don't think the bike needs or should have, is a major negative IMO. Since you can't have one without the other. I would chose for the less weight, and complexity and prefer not to have the system. Even though I do think the TPS itself is worth while (even with the extra cost of sensor replacement). But as a whole, I would prefer that the systems (remember there's more than one tied together) not be on the bike. This is because I could not just choose the TPS alone.  ;)
 
You actually can choose TPS alone - as an aftermarket system.  A quick Google search shows a variety of them available for bikes under $200, which is actually pretty reasonable for a nice farkle.
 
There are several factors that influence the accuracy of your TPMS, and you have to keep in mind that it contains a temperature sensor and a temperature compensation circuit inside the chip in the wheel sensor that attempts to compensate the pressure readout as the temperature in your tire goes up. The system is designed to have the "set" pressure done at around 68 degrees F, and in general, you should increase/decrease your "set" pressure about 1 psi for every 10-12 degrees F away from this temp set point. Hence if you want your tires set at 42psi, and your bike sat overnight in a 55 degree garage, you'd only need to pump them up to about 41psi. If it was 80 degrees in your garage, you should set them at about 43 psi.

The other thing you need to know is that your TMPS sensors work a little differently than most gauges, since they don't have a reference to ambient pressure available to them. They use a very tiny chamber inside them that is pressurized to sea level (0 psi or 1 Bar). This is used as reference value for the pressure transducer to measure the difference against. Most standard digital gauges use outside ambient pressure, so they are measuring the differential between the pressure in your tires and current outside barometric  pressure (otherwise known as gage pressure). And since the barometric pressure fluctuates with weather, this can also be a factor, as can altitude. So depending on weather and your local altitude, you may never get your TPMS to read exactly the same as your digital tire gage.

Also, the humidity content of the air inside your tire can play a factor in how accurately your TPMS reports pressure, since air with more moisture in it will expand more than dry air will when it warms up. You should try to use a compressor that has a drier on it when you fill your tires to keep moisture out of them.

I check mine at about 800ft elevation, and if I'm careful to set them at the proper set point temp, they generally are within 1psi of my digital tire gauge standard I use. I also use a drier snake on my hose when I fill them to keep the air in them as dry as I can.

I also wouldn't even waste time or money on mechanical tire gauges anymore. The mechanical parts in them induce error, and even a cheap digital gage will usually be far more accurate than even an expensive bordon tube gage. Digital gages also don't suffer from parrallax errors. Accutire make some of the better digital gages I have used, and even the $5 keychain ones on Amazon.com (Accutire MS-4652B) are very accurate.
 
Fred_Harmon_TX said:
There are several factors that influence the accuracy of your TPMS, and you have to keep in mind that it contains a temperature sensor and a temperature compensation circuit inside the chip in the wheel sensor that attempts to compensate the pressure readout as the temperature in your tire goes up. The system is designed to have the "set" pressure done at around 68 degrees F, and in general, you should increase/decrease your "set" pressure about 1 psi for every 10-12 degrees F away from this temp set point. Hence if you want your tires set at 42psi, and your bike sat overnight in a 55 degree garage, you'd only need to pump them up to about 41psi. If it was 80 degrees in your garage, you should set them at about 43 psi.

The other thing you need to know is that your TMPS sensors work a little differently than most gauges, since they don't have a reference to ambient pressure available to them. They use a very tiny chamber inside them that is pressurized to sea level (0 psi or 1 Bar). This is used as reference value for the pressure transducer to measure the difference against. Most standard digital gauges use outside ambient pressure, so they are measuring the differential between the pressure in your tires and current outside barometric  pressure (otherwise known as gage pressure). And since the barometric pressure fluctuates with weather, this can also be a factor, as can altitude. So depending on weather and your local altitude, you may never get your TPMS to read exactly the same as your digital tire gage.

Also, the humidity content of the air inside your tire can play a factor in how accurately your TPMS reports pressure, since air with more moisture in it will expand more than dry air will when it warms up. You should try to use a compressor that has a drier on it when you fill your tires to keep moisture out of them.

I check mine at about 800ft elevation, and if I'm careful to set them at the proper set point temp, they generally are within 1psi of my digital tire gauge standard I use. I also use a drier snake on my hose when I fill them to keep the air in them as dry as I can.

I also wouldn't even waste time or money on mechanical tire gauges anymore. The mechanical parts in them induce error, and even a cheap digital gage will usually be far more accurate than even an expensive bordon tube gage. Digital gages also don't suffer from parrallax errors. Accutire make some of the better digital gages I have used, and even the $5 keychain ones on Amazon.com (Accutire MS-4652B) are very accurate.
Click to expand...

Moisture? Are we suggesting that we use pure nitrogen in our tires? (As opposed to the normal 79% pure stuff.)  :deadhorse:

What part of Texas, Fred?
I live about an hour west of DFW, on top of a "mountain" (a Texas mountain, not a Colorado mountain), so I usually fill my tires at about 1200 ft elevation. Most of my riding is done between 600 and 800 ft though. What's the psi difference between 1000 ft and sea level?
 
I find it to be very accurate. I would assume if one went bad it would be obvious. I would imagine a low tire is very noticeable due to the weight of the bike.
 
wally_games said:
I usually fill my tires at about 1200 ft elevation. Most of my riding is done between 600 and 800 ft though. What's the psi difference between 1000 ft and sea level?
Click to expand...

Ignoring weather conditions, the difference in pressure between sea level and 1,000 ft is about .626 PSI.
 
Fred_Harmon_TX said:
Ignoring weather conditions, the difference in pressure between sea level and 1,000 ft is about .626 PSI.
Click to expand...
Interesting - I'm at around 1,800 feet above sea level.
 
Glennn said:
Fred_Harmon_TX said:
Ignoring weather conditions, the difference in pressure between sea level and 1,000 ft is about .626 PSI.
Click to expand...
Interesting - I'm at around 1,800 feet above sea level.
Click to expand...

Ignoring weather, at 1,800 ft, the difference from sea level is about 1.1 psi.

http://www.calctool.org/CALC/phys/default/pres_at_alt

If you factor temperature and/or humidity changes into the equation, it gets a lot more complicated, but this will get you in the ballpark.
 
Taking Fred's comments and Bob's comments and kinda rolling them into a thought - I use a digital gauge to set my tire pressure and the TPMS readout to tell me when something's seriously wrong.  Personally, I can't tell the difference a lb of air, one way or the other, makes.  And I agree with ChipDoc - if you don't have 'em, get 'em. :motonoises:
 
Well lets remember I started out the thread with the TPS reading 37psi and I'm chasing 42psi - a 5psi difference, in my opinion, is a fair whack. :)
 
Glennn said:
Well lets remember I started out the thread with the TPS reading 37psi and I'm chasing 42psi - a 5psi difference, in my opinion, is a fair whack. :)
Click to expand...

Glenn, my guess is part of the problem you are having may be due to high moisture content in the air in your tires. It will help if your air source you use to fill your tires with has a drier on it. It will also help if you try to set your tire pressure at or near 68 degrees F.
 
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