I haven't checked the air pressure in my tires since it got cold out, I haven't driven it much. The door tag calls for 35 psi front and rear. Well today I checked them, it was about 60 degrees outside, and they only had about 26lbs in them. That is close to 30% below the recommended pressure. I would have thought the message center would have set off a message, but nothing came up.

At what point does it set off an alarm? I would think near 30% would trigger something?!?!?

I put them back up to 35 cold, not driven (it was 60 degrees outside) but what about when it gets to 95-100 degrees like it does here in the summer?

I thought it was riding rough a few weeks ago, I can't imagine how rough it will ride now that I added more air to the tires.

 

Tire pressure decreases and increases proportionate to temperature. That's why they measure them "cold". They will vary and increase slightly when heated up from driving. But on average, you will lose approx. 1 PSI of tire pressure per month.

TPMS sensors work in conjunction with ABS speed sensors(If I recall correctly, if I'm wrong I'm sure someone will chime in but I worked at a tire shop for 3 years when they started using them so I might be wrong now). They basically work with them to tell differences in wheel speed to judge low or high pressure. They will not specify a wheel in question or if it's high or low. But how it reads them is by difference in wheel speed. Long story short, if all the tires are within approx 1-2 PSI of each other(higher or lower) it will not show the TPMS light.

Hope that helps.

 

I realize that temps have an affect on tire pressure, that's why I measured them "cold". But what constitutes "cold"? Is it "cold" in Minnesota, or "cold" in Florida?

I just thought that with all 4 tires almost 10lbs low (which is almost 30% below the recommended pressure), something would have went off. It kind of surprised me when I checked them that they were that low and no message had come up.

 

Checking them cold = no heat in them from driving.

 

But like I said, what constitutes "cold"? Nathan's "cold" or the "cold" we have down here? -10F or 50F? What exactly is "cold"? It hasn't been driven in over a week, but over that week it has been as warm as 70F and as cold as 18F, what is the real tire temp to go by when its been sitting there?

 

I think 'cold' refers to basically the current outdoor temp whatever that may be that day. And the tire is that same temp until you drive. Then the heat build up makes it hotter than the outside air and the tires start to build more pressure. Its not referring to Canada cold vs Colorado cold.

 

I realize that, but like I said before, what do you do when its been sitting in the garage and not driven but its been in the teens one day and 70+ the next day?

That's a big swing when trying to determine what to go by when reading the door sticker that says "35 psi COLD". Hell, "cold" here could be a huge range depending on what time of year it is (if you're calling cold the temp it is when it hasn't been driven). "Cold" in January could be 10 degrees, but "cold" in June could be 105 degrees.

 

They mean not driven. I understand the change in temps each day. You should check them if today is 30* and you last checked them at 70*.

I also have to watch if the car is parked in the driveway and only one side is getting sun (spring and fall the sun is pretty slanted here - 42* lat). The sun is pretty intense because of 4200' and it makes a difference of up to 2# depending on the sunny vs the shady side of the car. So I check them as soon as I back out of the garage.

I have the same issue with change of altitude. So if I'm going for a hard cornering drive down to the valley all I can do is check them before I leave. They will increase in pressure not only from driving them but from dropping altitude. But when I return home and park, when I check them the next day they are almost always right on the money.

I have learned for extra stickiness down a certain road to Ashland, that if I drop to 30 (mine call for 32 cold) they stick better. Prob because by the time I get heat in them and drop a few thousand feet they're prob up to 35ish+ from 32* - which provide less traction with the KDWS.

 

Well anything under 70 degrees and these Goodyear F1:G2 are like hockey pucks, with this kind of torque you can lite them up at 60-70 mph with ease when its cool outside (60 degrees). They are worthless until you get some heat into them. I was just wondering what kind of cold (not driven yet) temps they should be at. I don't want to wear them out on the outside if they are too low or the inside if they are too high considering how much it costs to replace these tires ($1500-2000) and they only last about 10-15K miles.

 

I never let the tire pressure get low enough on the Shelby to have it go off but on the other two DD it seems as if both went off when a tire went below the 26lb range.

 

The OEM tires/wheels had a small leak in them on the left front; the tpms sensor went off at anything below 30 psi. Took it to the goodyear place around the corner from my house, they remounted, balanced and resealed the bead and I never had an issue with them afterwards (1000 miles). My OEM's were the same tires yours are, RBB.

Re: cold tires, ambient temperature is considered cold, regardless what ambient temperature is (19F or 90F). I know what you're asking, and the answer is conditional, because what you're really asking is how hot the tires get when they're "warm", and how big the difference is between THAT temperature, and whatever is referred to as "cold." I would say that anything below 40F is going to be negligible, since they're "not supposed to be driven in temps below 40F" (in quotes because it's what the manufacturer says about the tires themselves). The easiest way to get an answer, honestly, is to take readings at the coldest point of the coldest days, and contrast that with readings at the warmest points of the warmest days. The difference in temperature will tell you what the rate of change is for the pressure. If the difference is >5lbs, I would adjust the pressure accordingly (add air if it's low in the cold, remove it if it's high in the heat). It would also help if you could get an idea of what Goodyear considers the tire's "optimal" operating temperature. I would imagine that info is available somewhere, though you might have to dig around the net for it. Heck, you might want to shoot an email to Goodyear support and ask them your question; they might be able to give you some solid numbers to use without you having to do any measurements yourself.

Edit: I realized after reading this that it's a bit ambiguous; you won't be able to take the temp of the air inside the tire; rather, the tire pressure and the temperature of the tire itself will give you an idea of the air temp inside the tire. It's the internal air that increases the pressure on the tires, the temp of which naturally can't be measured.

 

Yeah, I got kind of sidetracked on the temp issue, but what you stated is what I was referring to on that point (mainly how much its going to rise during the summer).


The main point that I was curious about was how low they had to be before the tpms would give a warning. Interesting yours went off on anything below 30, and not a peep out of mine.

 

Back to a previous post that it ties in with the ABS, the difference is he had one tire that was low so it picked up the differential. Whereas all 4 of yours were low correct?

 

Yes. Didn't think about that. They all had 26 - 26.5 in them.

 

Last summer I dropped my rear tires down to 24 lbs. at the drag strip. The sensor did not go off until I left the track and had driven about 4-5 miles on the highway. It apparently is not an instant alarm.

 

I don't even have TPMS sensors in my winter tires/wheels, and the warning doesn't go off until I've driven the car for about 20 minutes.

 

Early Tire Pressure monitors used the ABS wheel sensors but very few, if any use that anymore. You will notice that the valve stem is no longer rubber. It is actually the top of a large device that fits inside the rim and measures the pressure directly. It is battery powered and sends the pressure wirelessly to the car. It goes to "sleep" when the car is not moving and takes a little while to wake up. Also, it only sends the pressure every so often. This is all to save the battery.
Check out tire rack to see what they look like.
http://blog.tirerack.com/blog/hunter...e-at-tire-rack

 

As stated it's all about the difference between all sensors when they're compared. If they're all reading the same pressure then they're going to act the same. If one is down 10psi compared to the others then you should expect it to go off. In my experience if all four are reading even 20psi together, the system will show no issues.

 

I understand the "cold" as sitting overnight (no driving). I check them every Saturday morning right before it gets backed out of the overnight sleep in the garage for its bath. I set the pressure to 34 pounds.

I do this now per the recommendations of my local tire shop. I had the TPS light come on once awhile back; the pressure was 27 in two of the 4 tires.

Since using the recommended Saturday check, I've not had a problem. I have 39K on these original pirellis, and the tire indicator is still "under" the tread.

Granted, I do not have the HP and TQ of your Mustang, and don't crank my rear tires as some might.