Accuracy of TPMS
Rennlist Member
Joined: Jul 2009
Posts: 5,963
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From: Vancouver, BC
I think I did this a while ago when I first was bothered by TPMS discrepancy. I'll do it again since I don't remember the details except to have become disappointed with TPMS.
I have three gauges, all non-cheap ones, in different cars, will try to test them all tomorrow or the next day. Got a feeling they will agree with each other and disagree with the TPMS. Why? because they're all electronic, two different mfgrs, two from same mfgr bought a year apart.
If they do disagree, I'll put the one that matches or closely matches the TPMS in the P-car!
Will report back.
I have three gauges, all non-cheap ones, in different cars, will try to test them all tomorrow or the next day. Got a feeling they will agree with each other and disagree with the TPMS. Why? because they're all electronic, two different mfgrs, two from same mfgr bought a year apart.
If they do disagree, I'll put the one that matches or closely matches the TPMS in the P-car!
Will report back.
So, if one is putting air in the car, your gauge shows it instantly and if you looked at the TPMC reading it may not be updated yet, since the larger discrepency.
Drifting
Joined: Dec 2009
Posts: 3,035
Likes: 15
Also, TPMS is slow to re-act. I remember when I had a flat and was trying to inflate without having a tire gauge... it was a few seconds behind before the pressure was updated... like I had to put air in, step back to the dash, wait for a few dozen seconds for the new pressure to be read.
So, if one is putting air in the car, your gauge shows it instantly and if you looked at the TPMC reading it may not be updated yet, since the larger discrepency.
So, if one is putting air in the car, your gauge shows it instantly and if you looked at the TPMC reading it may not be updated yet, since the larger discrepency.
I hope I can get some sleep I'm so excited! (joking
)
Racer
Joined: Nov 2009
Posts: 335
Likes: 6
From: Seal Beach, SOUTHERN california
My understanding is that TPMS is highly precise, but inaccurate.
that is to say, it cannot be calibrated so the absolute values are off, but once you know how to translate the TPMS #s into the real tire pressures, it is very precise. that is to say that it will reliably show tire pressure fluctuations to within a fraction of a PSI (argh, PSI is so medieval)
that is to say, it cannot be calibrated so the absolute values are off, but once you know how to translate the TPMS #s into the real tire pressures, it is very precise. that is to say that it will reliably show tire pressure fluctuations to within a fraction of a PSI (argh, PSI is so medieval)
Rennlist Member
Joined: Jun 2001
Posts: 3,295
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From: Bay Area CA
Mine is consitently off by 3-4 pounds per tire, and it likes to show a difference left right that doesn't exist - at least if the Tire Rack Psiclops is accurate (it inflates both sides to the same pressure at one time)
it useless for anything but notifying you of a true flat tire...
it useless for anything but notifying you of a true flat tire...
Three Wheelin'
Joined: Jun 2009
Posts: 1,835
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From: ATL
Strange stories - I have Porsche guage, an Accutire, another on the pump ($50 Home Depot - nothing fancy), and the TPMS. The Accutire and TPMS have the most detailed readouts respectively, but even when I compared with the other guages, they are all close - I use the one on the pump to give me an idea when I am close and I usually am within 1lb. Then I use the Accutire to bleed off any over - and the TPMS agrees +/- .5lb - all way more accurate than I think is necessary.
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Joined: Apr 2002
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From: Los Angeles, CA
Gen1 TPMS was very slow, in particular to calibrate.
Gen2 TPMS is very fast and fairly accurate and more reliable
It's purpose is to let you know you are loosing pressure.
There is no substitute for a good tire gage....
Gen2 TPMS is very fast and fairly accurate and more reliable
It's purpose is to let you know you are loosing pressure.
There is no substitute for a good tire gage....
Drifting
Joined: Dec 2009
Posts: 3,035
Likes: 15
Okay, Here are the test results as promised (what I do for you guys?!).
Three are electronic units by "Accutire," whatever the heck that means nowadays. All three definitely bought at different times and places. The other round unit is a good quality mechanical item bought at a speed shop years ago.
Anyway, gotta hand it to the "Accutire" people. I guess they prove it isn't hard to manufacture a consistent product. I don't know about you guys but I gotta bet they're accurate too. Why go for consistency without ACCURACY?
Result: Get with it and stay with it Beru/Porsche! If "Accutire" can do it! You should too! I dunno..., I guess 1.5 lbs isn't a big deal but it DOES bug me. Nah..... It's not as bad as I thought it was.
BTW, Givens: Car is hot, just parked, TPMS noted on paper, I was very careful not to leak significant air during the four tests on front tire. Back tire? Testing order of units is different from front tire. Also very carful about air leakage.
Three are electronic units by "Accutire," whatever the heck that means nowadays. All three definitely bought at different times and places. The other round unit is a good quality mechanical item bought at a speed shop years ago.
Anyway, gotta hand it to the "Accutire" people. I guess they prove it isn't hard to manufacture a consistent product. I don't know about you guys but I gotta bet they're accurate too. Why go for consistency without ACCURACY?
Result: Get with it and stay with it Beru/Porsche! If "Accutire" can do it! You should too! I dunno..., I guess 1.5 lbs isn't a big deal but it DOES bug me. Nah..... It's not as bad as I thought it was.
BTW, Givens: Car is hot, just parked, TPMS noted on paper, I was very careful not to leak significant air during the four tests on front tire. Back tire? Testing order of units is different from front tire. Also very carful about air leakage.
Drifting
Joined: Apr 2002
Posts: 2,958
Likes: 107
From: Wilmington, NC
I think the key is to check the tire pressure ea time you drive regardless of methods and look for pressure drops. LIBR that's pretty funny, thanks for sharing. Now I know not to depend on mine, I have 2 of those pictured plus my favorite from Radio Shack.
