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Old July 11th, 2003, 11:11   #1
DMM
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Default Difference Between Cold/Hot Tire Pressure

I know this is probably not the most intelligent question but does anyone know the general difference between cold tire pressure and hot tire pressure.

Meaning if the cold tire pressure is 30psi what is the likely hot tire pressure psi?

Also how much driving does it take to reach "hot" tire pressure?

Thanks,
DMM
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Old July 11th, 2003, 12:20   #2
spicy_red
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Default Difference Between Cold/Hot Tire Pressure

Maybe 3-4 pounds?

Hot driving... uumm tough one.
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Old July 11th, 2003, 12:20   #3
dieseldorf
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Default Difference Between Cold/Hot Tire Pressure

the differential is probably 3 - 4 psi. It's best to check your tires in the AM assuming the car sat overnight.

I suspect it takes several miles of driving for your tires to begin warming up.
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Old July 11th, 2003, 12:23   #4
SwimmerDave
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Default Difference Between Cold/Hot Tire Pressure

No more than a few pounds for most people, where "most people" means:

a) 80% median of the tires used
b) 80% median of temperature changes

Where you would fall out of the norm would be temperature changes of say 50 degrees or more (it's 32 degrees in the morning and 30psi and who knows how many PSIs when it's 82 in the afternoon and you're driving on the highway) and/or non-mainstream tires (racing tires, for instance).
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Old July 11th, 2003, 13:48   #5
jjvincent
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Default Difference Between Cold/Hot Tire Pressure

For non-mainstream tires (racing tires, for instance) you might have 35psi cold and 45 to 48 hot. For a street car, if you want to keep your tires properly inflated, just be consistent. Try this; Check the tires in the morning after the car sat the night, even if it is the winter or summer. You'll be just fine.

If you really want to worry about it, then you better take into account the barometric pressure, altitude and gauge variation. What about using nitrogen? What are the tire temps? What is the asphalt temp? How about heat cycles? Durometer readings? Do you make more left turns or right turns? Should you let the air out of the tires overnight and let them "rest"? What about the valve stem inserts and Coriolis Acceleration?

As you can see, the tires can become quite complex if you look into it too much.
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Old July 11th, 2003, 14:20   #6
ruking
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Default Difference Between Cold/Hot Tire Pressure

Quote:
I know this is probably not the most intelligent question but does anyone know the general difference between cold tire pressure and hot tire pressure.

Meaning if the cold tire pressure is 30psi what is the likely hot tire pressure psi?

Also how much driving does it take to reach "hot" tire pressure?

Thanks,
DMM
There is actually a lot involved, but to cut to the chase, here are some ball park fiqures. Operating temperature adds between 3/4 #'s. Try it out, before you take, say a half hr freeway trip, get a "cold" reading. Assuming NO ambient temperature change you should get 33-34 psi (operating) with a cold pressure of 30 psi. It takes as little as 1 mile to go from cold to "hot."

Also for every ten degrees of temperature change it represents #1 of change. So a 30 psi cold checked at 50 degrees should be 35 psi cold at 100 degrees (variations like this are common in the desert for example) Since sun can also shine on the tires. (and black REALLY absorbs heat!!) I have pumped up (cold) tires EXACTLY the same and have the sun shine on two of them and the difference can be as little as 2#'s (so a minimum of 20 degrees difference)

On a recent trip in a Z06 Corvette, I went from 104 degrees to a low of 20 degrees,(84 degrees of variance) not to mention snow, rain, altitude and intense desert sun!!
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Old July 14th, 2003, 13:37   #7
rexhart
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Default Difference Between Cold/Hot Tire Pressure

Quote:
...Coriolis Acceleration
Wow that is deep. As for how long it takes to get a hot tire I agree with ruking: there is a lot of friction on the tire and it doesn't take long to get "hot"
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