Summertime tire pressures - what counts as "cold" for setting tire pressure

[Neggytive]

Before you drive the car and add heat to the tire by friction, Heat causes pressure to go up, by way of Boyle's Combined Gas Law

That is why you get a low pressure warning when the tires you filled at 75 degrees ambient sit outside on the first cold night of fall or winter and drop to 40 degrees

Normally your pressure will go up about 3 degrees when you drive the car and get some heat in the tires.

Set the TP hot, the car cools off, the pressure drops 3 PSI or more, and we are looking at the Ford / Firestone fiasco of the 90's, which is why we have Federally mandated TPMS monitors

If you notice the TPS monitor comes on at about 2 to 3 pounds below its target pressure.

So my answer is... when the car has sat for a while, overnight is better, and has no added heat that would cause the pressure to be higher than it would at static rest

https://chem.libretexts.org/Bookshe...The_Behavior_of_Gases/14.06:_Combined_Gas_Law

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[fishinrich]

Use common sense and you'll make it through this.

 

[ChitownStang]

I have always done 32psi cold.
That’s what is recommended in your door sticker.
Always had great traction and tire wear

 

[Achlys]

Cold tire: sitting for about 8 hours in the shade. Pressure should read at the proper PSI from your driver's door panel.
Hot tire: a tire that has driven over 1 mile. No, it is not ready to drag-race; only the tire's interior temperature affects PSI.
Cold weather: based on regular air, not nitrogen, for every 10 degrees drop in ambient temperature, a tire will loose 1 PSI. So if you go a month, say in October when temps change, your PSI could be low, which could affect tire wear and traction. Nitrogen removes the majority of these issues.
For the OP, messure the tires at the outside temp, after a mile or so, they will warm up to the proper temp. Or find a retailer that uses nitrogen, and all will be well. Nitrogen does not fluctuate like regular air, hence the reason nitrogen is used in jet plane tires.

 

[MCS]

I run 32 cold in the summer
I run 32 cold in the winter when it's sitting in my garage

I have a portable air pump that I set to 32 every 6 months.

 

[LouG]

What did surprise me was the 32 spec. It seemed low, my last car had 42psi Fr and 30psi Rr for 245/35-20 tyres.
But it works

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