Tire Pressure when Cold

[astrotoy]

According to the sticker on the car, the cold tire pressure is listed at 33 PSI. I filled my tires to 34 psi and normally, in the morning they are 34 psi. Our temps in the morning are typically in the hi 50's or low 60's (SF Bay Area). However a couple of weeks ago the temperature dropped to the low 40's, horror! Any way the pressure was down to 32 psi. If I were in a colder clime, with the temperature falling below freezing - then the pressure should even be lower.

So if I were to have the cold pressure at, say 36 psi, under our normal morning temps, then that should be about 33 psi if I were in Juneau or some other cold place.

BTW, the highest pressure my tires get, after 30 minutes on the freeway at 80 mph, is about 38 or 39 psi.

Any advice? Thanks.

[rominl]

it's a guideline, there is no "must", so when it's cold (even say winter norcal cold), if you are around 33-34psi, you are good to go

[Mike_TX]

I have Michelin tires on my car, and I have noticed they seem to fluctuate a lot with temperature - both the air temp and tire temp.

But like Rominl says, if you tried to always keep your tires right on the exact cold pressure you'd drive yourself crazy with the air hose. The 33 psi pressure is an average, and you'll surround it over a period of time ... sometimes it'll be higher, sometimes lower, but it'll average out. By way of reassurance, I've seen pressures rise from 33 cold to 40 psi after running fast in hot weather.

The only half-way solution is to inflate with nitrogen. It's available for a small charge at places like Costco, many tire stores and some repair garages (and even afew Lexus dealers).

I've used nitrogen before, though, and it isn't a perfect solution at all. The pressures still fluctuate.

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[jmcraney]

Up to 1 PSI change per 10 degrees F is considered normal - up for warmer, down for cooler. You should inflate your tires to 33 PSI on a typically cold morning before you drive. The tire pressures displayed in you instrument panel should read 32 or 33 (for the tires on the ground) as you start to move for the first time in the morning. The permeation loss is covered up by the seasonal change from winter to summer. But the permeation loss is magnified by the transition from summer to winter. We will soon see lots of comments from owners having TPMS problems.

[Nospinzone]

So if I were to have the cold pressure at, say 36 psi, under our normal morning temps, then that should be about 33 psi if I were in Juneau ...

And if you drove up to Barrow, you'd need run flat tires!

[snoylekim]

hmmmm...could it be BOYLE'S LAW .......