TPMS (Trailer Tire Pressure Measurement System)


Below is the text of an email that I wrote to a NASA type in response to his questions re. my TPMS system.

Preface. I’ve had lots of trouble with trailer tires. Most years I’ve ended up with 4 flats. Replacing a trailer tire on the side of a freeway, in the dark, potentially in the rain, with cars zooming right by your ass at 80mph is more dangerous than anything else you’ll do with SpecE30.

TPMS does 2 things for you.

  1. It ensures that you don’t start a roadtrip with a trailer tire that is low. The common wisdom is that’s the #1 cause of trailer tire flats. This assumes that you have a good TPMS system that talks to your display unit all the time like an OEM system. If you have a crappy TPMS system than it might only talk to the display unit every 20min or so. In that scenario you start out on your roadtrip with a display unit that is showing you information from the last time you turned the unit on, which was probably a month prior.

  2. It ensures that you are immediately told of a tire pressure problem, to include a blowout. I can usually tell if I’ve lots a tire, but “usually” isn’t “always”. There’s been a couple times when I detected no sound nor vibration clue re. the flat so I drove a ways on 3 tires. There’s all sorts of ways that could go really bad, to include the “3rd tire” getting way overstressed and suffering internal damage that leads to it’s premature failure.

The TPMS system I settled on is by an outfit names TST. The first two that I tried hard to make work, but ultimately couldn’t get them to be reliable were TyreDog and TireMinder.

Not only is the TST unit more reliable, meaning it’s display unit reliably receives a signal from it’s sensors, but it also gives you real time info. This is a big deal. The first two TPMS systems I had only updated every 20min or so. So I’d turn on the system and it would show me old psi/temp info from the month previous. Since the sensors were not all that reliable about transmitting new info to the display unit, it was always hard to be sure if I was looking at near real time (within 20min) info on the display unit, or if I was looking at last month’s info. The only way I could tell if the display unit was showing me new vs. old info was to make a judgement call re. the temp info it was displaying. Since the system was unreliable, it was very common to do an entire roadtrip with the display unit showing me month old info for one or more of the tires.

I got a flat on the way to CMP last year. I heard a bang and felt the vibration. My eyes immediately glanced at the TPMS display which was showing me no problem. I pulled to the shoulder of the freeway, got out and checked on the trailer tire. Sure enough, it was blown. Then I went back to the truck and fetched the TPMS display unit that still showed the tire as being fine. I set the display unit down near the exploded tire and took a fucking picture of the display unit, clearly showing the tire was fine, leaning against the exploded tire.

The TST unit shows you info only if it has real time info. That way you know for goddamned sure that you’re looking at new info.

Related thoughts.

Internal vs. external. I was, and continue to be, torn re. internal and external TPMS sensors. Internal meaning a design similar to OEM where the sensor is integrated into the air stem and is inside of the tire. External meaning you screw it on the air stem like a big cap. The perfect solution would be the simplicity, reliability, and battery of OEM internal TPMS sensors. But the fact that both of the two TPMS systems I tried to make work required so much dicking around with to keep them functioning made me very reluctant to get a system that was difficult to get to. If an external TPMS sensor isn’t registering on the monitor, it’s easy to remove and replace it. That’s often enough to get it going again, altho it seems to help to have the monitor with you, instead of in the truck, when you do it. If that doesn’t work, you can easily replace the battery. But if you have an internal unit and it’s not registering on the sensor, what do you do, go to a tire shop and have them take the tire off of the rim so you can diddle with the sensor?

If you use external sensors, steel air stems are better than rubber. The external sensor puts stress on the air stem as the wheel rotates. If you have external sensors, then the next time a tire/wheel is in the shop, I’d direct the shop to install a steel air stem vs. a rubber one.

External sensors and air leakage. It takes some time to build confidence that external stems won’t cause an air leak. It wouldn’t be crazy tho to put a dab of goobage on the threads. Don’t overtighten the sensor, one might end up with damaged threads. Certainly the possibility of an air leak at the stem is a disadvantage for the external sensor. That hasn’t happened to me, but I did have one stem that was kind of “sticky” and therefore seemed to want a couple drops of oil when I put air into the tire each month. Otherwise when I removed the air chuck the stem would stick and air would come out. Remember, air stems are designed to spend their lives in the closed position and external sensors force them to spend much time in the open position.