TPMS accuracy

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Rogwp

Rogwp

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Has anyone been able to test the accuracy of the car’s TPMS readings?

My tire pressure gauge is a bit vague, but even with a digital gauge my readings are very different from the car’s. I get higher readings than the car, and the car shows imbalanced readings across axles!
 
I upgraded my digital inflator at home to a commercial-duty unit (±0.2 psi accuracy), and the sensors consistently read 1 psi lower, even though the tires have started warming by the time I’ve driven far enough to get readings.
 
SameGuy said:
I upgraded my digital inflator at home to a commercial-duty unit (±0.2 psi accuracy), and the sensors consistently read 1 psi lower, even though the tires have started warming by the time I’ve driven far enough to get readings.
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That’s my experience too, it’s really hard to get accurate readings from the car as the tires are getting warmer each time I try! (OCD is a wonderful thing?). :)
 
ColdCase said:
I'm missing something, why is that a problem? Are they suppose to balance automatically? The sensors are independent.
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What seems to happen is that to get the exact same reading on the two tires on the car I have to adjust one tire so that it reads higher on my gauge than the other one. Then the car shows balanced readings for both tires. Could just be that one tire is a little below the car’s reading and the other a bit above. Of course every time I test them they are getting warmer!
 
It’s more likely that both the sensor and your inflator are within their margins of error, so 38 psi to the inflator on one tire might actually be 38.3, and 37.7 on the other, while the sensor might decide one is 38 and one is 37.
 
SameGuy said:
It’s more likely that both the sensor and your inflator are within their margins of error, so 38 psi to the inflator on one tire might actually be 38.3, and 37.7 on the other, while the sensor might decide one is 38 and one is 37.
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That makes complete sense to me, thanks. I also noticed that the car shows different readings at first (when I start out) then shows the two tires having the same reading when they have warmed up a bit.
 
I mean we’re not running the inside groove at Talladega, so it’s a little OCD and inconsequential as far as real worries go, but I totally get it; it bugs me so much!
 
Mathematically, if the sensor is within 1psi of actual, it is possible the TPMS could show a 2 psi difference between tires that are actually at the same pressure. One sensor 1 psi high, the other 1 psi. Folks that want to set the tire pressure precisely use a calibrated gauge.

Keep in mind also that the TPMS sensor is indicating absolute pressure inside the tire, not relative pressure to atmosphere like an external gauge would. You want to inflate your tires to relative pressure to get the ideal ride and profile you want.You can get a 4psi difference between 10000 feet and seal level. Lots of folks get low TPMS pressure warning when driving at altitude when the tires are actually inflated to spec (relative). So you may need to consider what altitude you are making your measurements to determine how accurate to expect the indicated pressure to be. I believe the sensors are calibrated for sea level.

... It's easier to just make sure the tires are still round... and go ride.
 
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By the way, if you are checking tire pressure at 2000 feet altitude or so you would expect to see about a 1 psi difference between TPMS and external gage values, if both are spot on accurate.
 
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SameGuy said:
I upgraded my digital inflator at home to a commercial-duty unit (±0.2 psi accuracy), and the sensors consistently read 1 psi lower, even though the tires have started warming by the time I’ve driven far enough to get readings.
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I'm looking at replacing my home tire inflator - what model did you get? Mine has a really in-accurate gauge on it. :(
 
That said, I’d love to get an auto-inflator some day. Just set, hit the button, done. But $200 seems a bit much for the few times a year I’d need it.
 
I have been using an highly rated Makita DMP180ZX 18V Cordless Inflator for a couple years. It seems to be accurate, digital guage, consistent, durable, well made. Sets in 1 psi increments. I got it for free as part of a buy one tool, get one free sale, so the price was right. Otherwise $140 if you already have the batteries, $240 with battery and charger. This is one of those you get what you pay for decisions, which is subjective.
 
SameGuy said:
I got the JACO FlowPro 2.0 — it’s on sale right now at Amazon for $38!
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The river site is somewhat confusing, at least for me. This FlowPro appears to be a gauge, and not an inflator. Others listed as inflators appear to be only gauges, so you connect the air at one end, and use the hose attached to the unit to connect it to the tire. The Makita seems to be a true inflator. Maybe the site is just messed up.
 
I think most people think of an air valve with a gauge and a Schraeder chuck of some sort as an “inflator.” An “automatic inflator” just stops at a preset pressure. The air source doesn’t need to be part of the assembly — though there are literally hundreds of “portable inflators” listed on Amazon.
 
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