People Say...

[cmartyn]

People say TPMS sensors are not accurate. I guess I got eight magic ones.

[VStar650CL]

Depends on how you define "accurate". They don't generally give lab quality readings, so sticklers who want their pressures identical to a gnat's butthole will probably be disappointed. In my experience, modern ones are usually good to about +/- 1 psi. With some of the earliest systems the criticism was justified. They could be pretty crappy, especially when their batteries ran low.

[cmartyn]

Yeah.. keeping it dead nuts is crazy, I'd have to add air when I had people in the car and stupid stuff like that.. These all match my gauge exactly as well as each other.. temp is dropping by 30 degrees today, might get snow tommorow!

[firebirdude]

Sensors are just an idiot light for people who don't routinely check their tire pressures. Don't rely on them to be super accurate, but rather just alert you that A) you've forgotten to add air routinely or B) you've got a leak. That's it.

[cmartyn]

I was just surprised to see how close they matched my guages. I set them to 31.5 and 34.25 and voila. I'm going to keep on top of these since I don't drive much anymore I'm hoping to get 5 to 7 years or so out of the OEM tires.

[VStar650CL]

Sensors are just an idiot light for people who don't routinely check their tire pressures. Don't rely on them to be super accurate, but rather just alert you that A) you've forgotten to add air routinely or B) you've got a leak. That's it.

Yep, +1. There was a poll on another site about the general utility of TPMS, and my answer was both "useless" and "very useful". For my car it's the former. On the wife's car it's invaluable, the "funny yellow light" has saved a lot of grief over the years.

[KoiMaxx]

I do try to check the pressure with my tire gauge every month. But with temperatures here sometimes hitting 25-30C below 0 (minus 13-22F) this season, admittedly I usually just defer to the TPMS. Though I make it a habit of checking it as soon as the sensors can pull a reading every time I drive.

[PalmerWMD]

On my Nissan 2 of my TPMS are from this year and the other 2 are years old from a previous owner.

So even when all 4 wheels have identical pressure (35.5 psi according to my handgauge) I get 2 readings for 36 (from the new ones) and two readings for 33 (ish) from the old ones.
..or thereabouts.
When one side is is parked in sunshine and the other side in the shade it also makes for different readings but of course those reflect actual different pressures.

[cmartyn]

There is probably something to the fact that as the batteries age the voltage drops and this causes low readings. Something to keep an eye on 4 sure.

[VStar650CL]

There is probably something to the fact that as the batteries age the voltage drops and this causes low readings. Something to keep an eye on 4 sure.

I haven't done any empirical testing in situ, but I have had several types of sensors apart and working on the bench. I can tell you they all use either dual slope or differential slope techniques to cancel out the effects of fading batteries on their sensor measurements. Modern ones all report their battery state as well, so I wouldn't expect to see much variation in readings between full-charge and almost-dead. They all had temperature compensation of some sort as well. The earliest ones from around '05~'09 had some problems (including corrosion issues, not just electrical design), but technology marches on. The modern types are all pretty darn good.

[cmartyn]

Thats cool. I guess they figured out that having them off by 1 or 2 psi would drive some people cray cray. Sort of like the 5 cent clock chips vs the 10 cent clock chips with temperature compensation. One loses three minutes a year and the other 3 seconds but the clock with the 10 cent chip costs 20.00 more. Anyhow. I now notice the drivers side front tire warms up faster than the others. Probably because my big fat butt is riding on that side.. or is it the transmission.

[PalmerWMD]

I think the difference in pressure reading between old and new may also be due to them being simple different manufacturers.
For example when u take 2 regular hand pressure gauges they also tend to read a bit different.