So the temperature dipped from a nice 86 yesterday to a cool 57 today. I expected this to happen so surely it did, and got a nice message showing check tire air pressure. I know for a fact by looking at it my tire pressure is fine. Question do I just pump some air to have the message disappear?

Curious to know what the actual threshold for having the TPMS go bunkers actually is

 

Regulations for TPMS are to alert after 30% difference in air pressure. If it goes off on the coupe you have a tire at 25 psi or less. Trust me, you can NOT visually see this. The tire will look perfectly fine. Check your pressure ASAP!

 

Tire pressure decreases by about 1 pound per square inch for every 10-degree drop in outside air temperature

 

Mine seem to be far more sensitive, it triggers when 1 tire differs by 2-3 psi from the others.

 

If your tires were filled at the dealer, they set it to the recommended cold pressure even though you just drove it there. This means it can be 2-4 psi below normal when "cold". Add in the ambient drop and it isn't too surprising that it went off.

These numbers are based of my TSX that gives real time pressure. We've dropped out of the 100s and it is now raining for the second time this summer. I am definitely checking the pressure in the morning.

 

I certainly agree, in spite of those who belittle TPMS because they “check their tires regularly” and therefore don't need it. The reality is one cannot necessarily “see” hazardous low tire pressure, and that’s what TPMS is designed to address before something bad happens.

 

If you have a TPMS indicator, the tire is low unless it's malfunctioning. Buy a tire gauge. Check them once a week minimum, every 2 or 3 days is better.

The lower the profile of the tire, the more difficult it is to visually detect if it's a little low.

My experience is that it comes on when they're about 8 or 9 psi low.

 

I noticed recently that one of my sister's tires seemed a little low, so I checked them. Three of the four had 23 PSI in them and the fourth (the one that looked low) had 17 PSI. The three that had 23 in them looked fine, and had the fourth not been so low, I wouldn't have even checked. Your tire's got to be extremely low for you to actually see that it's low. Steel-belted radials aren't like those old bias ply tires. They don't balloon up when they're overinflated and they don't look flat when they're low.

Your tires will lose a couple of pounds a month, and they'll lose a few pounds as the weather cools. If you last filled them up mid summer after driving on them for half an hour or while they were sitting in the sun, you probably have 10 pounds less, which would put them at 25 instead of 35. What was the TPMS threshold again? 25?

You should invest in a pressure gauge. You can get them at your local auto parts place for about a dollar. They're not perfect, but they'll do the trick. Check your tires every time you wash the car. It'll add about 2 minutes to your wash time, but it'll show you how much they fluctuate. In fact, check them once early in the morning before the sun hits them, then again after you go pick up something for lunch. If they're 35 in the morning, they won't be after you drive around at noon.

 

definitely can not tell 10 psi difference by eye. If the weather gets cold and the tpms goes off.. that means you do need more air. air shrinks the colder it is.

 

Thanks everybody, and definitely true. All four tires were at 30 psi vs. what is recommended on the door jams of 33 psi. I pumped it up and message disappeared, therefore TPMS did exactly what it should.