I have friend - fellow retired tire engineer - and he reports that those infrared surface thermometers don’t correlate well to the tire air chamber temperature. That’s because the road surface can be hotter or cooler than the internal temperature - and measuring the tread surface tells you more about the road surface temperature than the temperature for the critical part of the tire.
So its still better to monitor the pressure buildup - which shouldn’t exceed 10%, excluding ambient temperature effects ( 2% for every 10 degrees F.)
Ha, I never noticed or paid attention to the TPMS sensors being able to read the temp of the air in the tire, so great, now I am gonna have to hook up my scanners to see if any of them can read the tire air temp…
…and use which pressure value? The one on the door placard or the one in the owner’s manual?
The owner’s manual states to add 8 psi for high-speed operation, some are against this.
This debate has been going on for years, Robert wants to compare the tire temperature of the base inflation pressure to the temperature using the higher value.
For those who must know of their tires’ temperatures, Longacre Racing and other purveyors sell pyrometers, which measure the tread temperature - far more useful than knowing the temperature of the inflation gas inside (oxygen/nitrogen ). The probe penetrates about 1/16" into the tread surface.
A cooler middle tread, or cooler outer tread on both sides, more than 2deg F, tells of over or underinflation. Much warmer tread to one side or the other might indicate issues with camber angle.
I do sometimes use the IR thermometer when airing up my tires, but I do that early in the morning when the car or truck is in the shade. Under these circumstances the air temp inside the tire should be that same or very close to the outside air temp. It is just for verification that all tires read the same.
Then, using 20C or 68F as the base cold temp, I adjust the air pressure target by 0.1 psi for every degree that the actual temp varies from the base cold temp, up for hotter, down for cold. I also add 2 or 3 degrees because I do a lot of highway driving. But there are limits that I impose for my self on this, no more than 4 psi above the placard or more than 2 below.
My wife’s BMW X5 reads the temperature and displays what the pressure should be at that temperature (assuming you correctly calibrated the system when the tires are cold).
I always wondered how a DiscounTire or other tire store would calibrate a TPMS system, considering it may be the middle of the day, plus tires hot from driving there, etc.
PV=NRT , the ideal gas law. Because N, R, and V don’t change, you can figure out the temperature of the air inside your tire from the pressure. Do those TPMS measure it precisely enough? T is absolute, which is about 520°R for 70°F, so T would need to increase by 52° to result in a 10% increase in pressure. If you inflate to 30 psi, an increase of 17° would be 1 psi more, which seems likely.
I don’t understand your question. If a tire is ‘cold’, which is to say the same temperature as the ambient air, at 70°F, and 30 psi, then 31 psi after 30 minutes of driving, its temperature has increased by 520/30 = 17⅓°F. I can imagine a TPMS that reads to .1 psi, which would yield a precision of 1.7°F.
I think the term ‘cold’, in a tire context, is being over-analyzed, by many.
Cold simply means, either, earliest in the morning not yet driven, or, not driven for at least 3 hours.
Local ambient temperature figures little, if any, into this context.
I would like to know the groups thoughts on the following two cold tire inflation scenarios.
The first one represent s fairly steady daily temperatures, with a rising trend typical of June in north American climates. Instead of adjusting cold tire pressures at the coldest part of day, one could argue for adjusting them at the mid-point temperature, perhaps 3-4 hours after early dawn, as represented by the blue line.
One could argue that, but one would be wrong. When the manufacturer figures out the recommended tire pressure, they take into account that the temperature rises during the day.
The other point to make is that people can make more out of this than necessary or warranted. It’s really not that critical. If it was, you would see much more detail in the process of pressurizing your tires.
When I think of ‘cold tire pressure’, I interpret that to mean ‘before any driving that day’. I’m fine checking my tires at noon, as long as I haven’t driven up until then.
