Originally Posted by DoggieDaddy
Just to mention that it is important to know the temperature of the tire also. The chart pressures are at "cold tire" 65 degrees. The pressure in the tire rises with the temperature. When monitoring the tire pressure you need to adjust for the ambient temperature of the tire. The operating temperature of most tires is somewhere between 90 and 120 degrees depending on the day. If your tire temperature goes above that, there could be a problem. So you need a system that will alert you when the tire goes out of the temperature range also.
This is straying a bit off topic for the OP's question on whether a TPMS is a "yes" or "no" but perhaps some of my rationale for what it can do is close enough to the topic at hand.
Maybe I am misunderstanding what you just said. Let me clarify what Michelin says.
Michelin does not state what is considered a standard "cold" temp. See page 2 of link. BTW, I think I have seen some tire pressure calculators that factor in temps but I don't recall them having much to do with typical RV use. Perhaps the only use they might have is if you have one set of tires in the sun and need to compensate for that factor.
If the ambient temp is 80*, then that is your "cold" tire. It doesn't matter if it is 10* or 80*, if your tire chart says to use 100 PSI you use 100 PSI at the time you make any adjustments.
Now, if you drive from an area of 10* to an area of 50* and let the tires adjust to that 50*, you will find that your 100 PSI has increased to a higher figure because the higher temps expand the air inside the tire and increase the pressure. In that case one would need let the tires get "cold" and then remove air to bring the tire back down to 100 PSI. Of course, the converse is true.
there is also some impact of changes in barometric pressure but for the most part they are much more less a factor unless those changes are caused by significant altitude changes.
The 2 worse situations to be encountered after properly inflating tires are:
1. Encountering major DROP in temps.
2. Encountering major increase in barometric pressure such as driving from high altitudes down to lower altitudes.
In both cases that would reduce the tire pressure and, IMHO, low tire pressure is much more a problem then high pressure. Of course, if you are running tires as the max PSI, then high pressure might require a bit for attention.
The value of a TPMS is that it can help to help identify if those factors are significant enough to warrant action. Also, as a bonus they can help you know if tire temps are reasonably equal which is helpful when trying to avoid being fooled by tires heated by the sun.
FWIW, I set my TPMS pressure alerts to 5% below my target PSI and 25% above my target. My rationale is that I want to know quickly if a slow leak has encountered and also if colder temps have reduced my PSI. I am less worried about over pressure and found that 20% above target PSI gave me a few nuisance alarms.
BTW, I fire up the TPMS the night before I plan to travel to quickly see if my tires are within range and reasonably equal across each axle. From that I can generally predict if I will need to adjust tire pressure before I kick off the next day. I generally like to air my tires shortly after dusk for 2 reason. Tire temps should be reasonably "cold" and those temps should be reasonably close to early morning the next day unless other weather factors interfere.