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Al F

TPMS Limitations? Opinions??

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1 hour ago, Al F said:

Other than your statement seeming to say I am advocating anything at all about changing air pressure as we drive, we are in agreement.  I just don't see anything in my wording about adding or reducing air pressure because the pressure increases as we drive.

My reason for starting this topic is to discuss the possibility that some TPMS systems could alarm way to late for low pressure in a tire.

For example:  assume both steer tires have proper cold inflation of 90psi for the weight of the RV.  Now while driving on a hot day that pressure increases to 105psi (which is normal for the conditions).  However if one of the steer tires develops a slow leak the TPMS won't alarm until the pressure drops to 81psi (10% below the 90psi cold pressure).  That 81psi, given the driving conditions, as far as everything I have ever read about proper pressures, is way, way to low and the tire is likely to be rendered unsafe to drive on, even it it looks OK on the outside of the tire. 

Please reply with the reasons you may believe my above example is incorrect.

Let me preface by saying my comments are limited to the TST system, which I've been using for over nine years and is the only TPMS I've ever used.  Other systems may be as good or better, I just don't have any experience with them.

I understand the point you are making.  For discussion purposes, let's say that it is valid.  In answer, I would make two points.

First, the alternative would be to set the lower alarm at 89 psi.  At that point, it would be going into alarm regularly while the vehicle is stationary and the ambient temp dropped a few degrees.  It would be very annoying to me for every morning when I got in my vehicle to have all six tires going into alarm because the overnight temps dropped 10 degrees.  To me, the low pressure alarm is useful to alert me when I first enter the vehicle that I have a low tire.

Second, there are two more reliable methods to indicate if you have a tire which is losing air pressure while driving.  The first is visual.  That's why I bought a system which has a monitor with a psi readout for each and every tire.  I periodically check those pressures as I'm driving down the road.  If I have a slow leak, it will be obvious upon observation of the pressure readouts, that tire will have a lower pressure value than the others.  And, if the leak is more than a slow, gradual one, the system will alert me to a rapid loss.

Other than these thoughts, I don't have a solution for you to deal with the situation which you have envisioned.  I do know that in my years of using the system I've had two tires start losing air, one from a nail and the other from a tire separation.  Both times, the TST system alerted me in ample time to drive another 20 miles or more to have the problem addressed. 

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In reference to the comment on the limited value of the temperature readings with external sensors, I'll just say that our TST system's temperature readings have alerted us twice to non-tire related failures when the temperature rose significantly without a corresponding rise in tire pressure. One event was a stuck brake caliper on a previous toad, and the other event was a failing rear wheel bearing on the toad. The alerts from the TST monitor likely saved us significant expenses when we were able to resolve the issues before any major damage occurred. As far as I'm concerned, the system paid for itself with just those two events, not even including any tire related events.

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16 minutes ago, Dutch_12078 said:

In reference to the comment on the limited value of the temperature readings with external sensors, I'll just say that our TST system's temperature readings have alerted us twice to non-tire related failures when the temperature rose significantly without a corresponding rise in tire pressure. One event was a stuck brake caliper on a previous toad, and the other event was a failing rear wheel bearing on the toad. The alerts from the TST monitor likely saved us significant expenses when we were able to resolve the issues before any major damage occurred. As far as I'm concerned, the system paid for itself with just those two events, not even including any tire related events.

I absolutely agree.  It doesn't matter where the sensor takes it's reading.  If one tire/wheel/sensor is posting a temperature which is out of character from the other sensors, there is a problem which needs to be tended to.  Same with pressure readings.

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41 minutes ago, bigjim said:

Dutch, briefly how or why did it alert you to the 2 incidents you reference?

The failures generated enough external heat that they triggered a temperature alarm for the affected wheel, but the tire pressure did not increase proportionately. Of course the alerts didn't specifically tell what the failures were, but they did get my attention so I could check into them. I could feel the heat radiating from the overheated brake disc and smell the brake pads when I approached the wheel, so that one was obvious. The failing wheel bearing was found when I checked the wheel hub temperature.

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We had a similar issue. We had a very high temp reading on the left front truck tire sensor.Turned out to be a brake problem but it allowed us to stop before any damage or worse occurred We have been using the TPMS since 2006  both pressure pro and TST will not be on the road without it.

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