Tire Pressure Monitoring

As a general rule (i.e. I'm sure somebody could find an exception), the TPMS senders that are inside the tire have centrifugal switches of some sort and operate only when the wheel is turning above a certain speed, and do not have replaceable batteries. As already noted, the TST sensors transmit all the time regardless of tire rotation. They shut off when removed from the wheel. The auto industry is transitioning to "indirect" tire pressure sensing using the wheel speed sensors already in place for the ABS system. The advantage for the end user is no battery hassles, and the disadvantage is reduced accuracy. The advantage for the auto industry is that the indirect system is free on a per-car basis because it's all software.

Dutch_12078 wrote:
As the others said our TST 507 sensors report their readings even when standing still. We've been stationary on this site since last Sunday, and today I flipped on the monitor and had the current pressure and temp readings within a few minutes.

Correct

fj12ryder wrote:
"Before buying a high tech, super deluxe system check the price of battery replacement, up to $50 per sensor!"

FWIW the TST system using common button batteries. My last ones were about 30 cents each.

X2

JimK-NY wrote:
I have owned two Ram trucks with TPMSs. Both stopped working when the Truck stopped moving and would not update again until the truck moved for a few minutes.

It's very possible that those TPMS's worked in conjunction with the ABS sensors, and I don't believe they measure actual tire pressure so much as sense a difference in tire circumference and deduce a difference in tire pressure from that.

At least I've been led to believe that some OEM TPMS's work that way.

As the others said our TST 507 sensors report their readings even when standing still. We've been stationary on this site since last Sunday, and today I flipped on the monitor and had the current pressure and temp readings within a few minutes.

I have owned two Ram trucks with TPMSs. Both stopped working when the Truck stopped moving and would not update again until the truck moved for a few minutes.

fj12ryder wrote:
"Just try to understand how TPMS work. They go to "sleep" when you park the car and will be waken when wheels start rolling. Some system act faster, some need couple of minutes to start showing. So morning walk around still apply.
Battery replacement is another story as most of them are sealed and require whole sensor replacement. But sensors are getting cheaper and cheaper."

Well, a little misinformation there. Many TPMS don't go to "sleep" when you park. They are active all the time. You can see the air pressure in the tires shortly after the monitor is activated. I turn on the monitor when we start getting ready to tear down and leave. By the time I'm ready to hook up, the tire pressures are being shown. A walk-around is a good idea as it can alert you to issues.

Battery replacement isn't an issue since a lot of them are just weather sealed and batteries are a user-replacement item. You can get TPMS sensors that mount inside the wheel, but honestly who needs the aggravation.

Absolutely as fj12ryder says. My TST will show the pressures even if my 5er has not moved in days. And standard 2032 button batteries can easily be changed in a few minutes.

"Just try to understand how TPMS work. They go to "sleep" when you park the car and will be waken when wheels start rolling. Some system act faster, some need couple of minutes to start showing. So morning walk around still apply.
Battery replacement is another story as most of them are sealed and require whole sensor replacement. But sensors are getting cheaper and cheaper."

Well, a little misinformation there. Many TPMS don't go to "sleep" when you park. They are active all the time. You can see the air pressure in the tires shortly after the monitor is activated. I turn on the monitor when we start getting ready to tear down and leave. By the time I'm ready to hook up, the tire pressures are being shown. A walk-around is a good idea as it can alert you to issues.

Battery replacement isn't an issue since a lot of them are just weather sealed and batteries are a user-replacement item. You can get TPMS sensors that mount inside the wheel, but honestly who needs the aggravation.

Over 10 years ago I spend small fortune for TPMS system for my motorhome.
But than motorhome used 22.5 wheels and the Michelins I used retail $550 a piece.
So beside safety, if the system can save single tire from shredding due to low pressure - it will pay for itself.
New cars come with TPMS for a decade and California made checking tire pressure a part of biannual inspection so even government considers that important.
Just try to understand how TPMS work. They go to "sleep" when you park the car and will be waken when wheels start rolling. Some system act faster, some need couple of minutes to start showing. So morning walk around still apply.
Battery replacement is another story as most of them are sealed and require whole sensor replacement. But sensors are getting cheaper and cheaper.
Factory TPMS are mounted inside the tire, so you have to pay for tire removal on top of that. But I have factory TPMS on my 11 years old sedan and batteries still work after 180k miles.

agesilaus wrote:
Yeah well the physics are:

P1V1/T1 = P2V2/T2 where P=pressure, V=Volume and T-Temp in degrees Kelvin

Since V1=V2 you can drop that from the equation (yes volume may change slightly but we can ignore that)
and P2 is twice P1 then the temp in degrees K would have to double. Like from 270 deg K to 540 deg K and that obviously is not happening. That would be a 270 deg Celsius temp jump since our tires are not running at over 500 deg F. That's what physics says.

Good info. I once pulled into a rest stop and saw smoke rolling out of the left front tire. Turns out I had a caliper that was dragging for some longer period of time - and things were pretty toasty. My laser temp gun would not measure that caliper because it's limit was 1,000 degrees. I didn't think this scenario was even possible so I checked and double checked, but I can say it was still smoking when we finished our business at the rest stop. So we had lunch. My point is that I could believe that in rare circumstances temps can easily go over 500 degrees. But if that can happen then I wonder why my tire didn't blow. And no, I did not try measuring the tire temp ... Just saying ...