42/40 tire pressure gets 47/45 in hot afternoon

The max pressure is 44 psi cold. The manufacturer has taken into account pressure increases due to road heat, aggressive driving, etc.

You worry too much!

 

1 psi or so per ten degrees F. All accounted for in the safety
margins designed into the tires.
.
_H*

 

Well, we're testing the limits today and tomorrow: 102 today, 106 tomorrow... and the forecast estimates have consistently been lower than the actual high temp. I don't think I could live in Arizona.

I'm currently running at 38/36, so the temps haven't made the ride too rough.

 

I run 40/38 cold. It was 105+ yesterday here. You could hear the tar sticking to your tires as you drove down the road. Yuk.

 

Hi All,

I had this concern as well. So, I set the tires at 40/38 first thing in the morning, before the Sun makes it over the trees to where the car is parked. The dew point effectively limits the temperature drop, and probably the pavement temp drop. If anyhing were to try to get colder, the dew would form on it, and the latent heat of vaporization of the water vapor condensing on the surface would raise the object's temperature back up. Lately the dew point has been around 70 F or so. This method may not work for the desert dwellers out there. So, early in the morning (before 6 am here) when you see dew on the car, the asphalt and the air, and the tires are all at about the dew point temperature. Setting the tires at this time to 40/38 PSI if the dew point is 70 F allows a maximun service "cold" temperature up to 110 F if the 1 psi/10 degreeF is right.

How to get a cold temp when the sun is out is difficult. Measuring the tires a few hours later and one side of the car (shaded side) will still be near 40/38, but the sunny side will be 42/40, when the temp is still only 75 F. The black asphalt, and tires heat up from solar gain allot more from the sun of course. While one can measure the tire rubber temperature, the air temperature inside might not have caught up with any temperature variation in the recent history of the tire. Air does not conduct heat very well.

Yesterday was an extreme event here in Chicagoland. THI was at 110 F, with the air temperature at 95 F. They let us leave work early as the AC had failed on Thursday, and the repair was not complete till overnight last night (Monday). The Prius AC did a good job saving me from heat stress. In the morning I had to pick off a bunch a tar from the left front tire on the way to work to get the car road-worthy. The tar apparently came from where oil dripping from another car had sofftened a tar crack-patch in the 95 plus weather we have had on Saturday and Sunday. After 8 PM I went back out to get the rest of the stuff off the tire. The asphalt was still at 90 F plus.

So, I think to do this tire pressure setting right, you need the surface the car is on , and the tires to be cooled to the same temp, and out of the sun. As you probably have guessed, I do not have a garage.

 

"Cold" as it applies to tire pressures is a relative term that has nothing to do with needing a sweater. As long as you measure the pressure before you drive anywhere, that should be accurate. If it's beastly hot *and* you're loading up the car *and* you're going on a long trip, 42/40 might be pushing the margins of safety a little. But not that I've noticed so far!

 

zzz