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Author Topic: Spring Time PSI  (Read 1918 times)

Offline RunsinLight

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Spring Time PSI
« on: March 30, 2007, 06:51:57 pm »
I just checked my tires today a month after my last oil change and I find 38-40 psi in each. 35  psi is what the vehicle calls for. Any particular reason they would do this in the spring time?
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Offline dr_spock

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Re: Spring Time PSI
« Reply #1 on: March 30, 2007, 06:55:40 pm »
PV = nRT

Pressure is directly proportional to temperature. 

It's warmer so your pressure is higher given that the volume of air in the tire hasn't changed.
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Offline RunsinLight

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Re: Spring Time PSI
« Reply #2 on: March 30, 2007, 07:03:04 pm »
Quote from: dr_spock on March 30, 2007, 06:55:40 pm
PV = nRT
Pressure is directly proportional to temperature. 
It's warmer so your pressure is higher given that the volume of air in the tire hasn't changed.

Well know I'm certainly confused.

what you said makes sense, but how do I get an accurate reading on my tire pressure then?  If my pressure is 40 and its +10 out. Your saying I would get Example: 35 PSI tomorrow if the temperate was -10?
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Offline Allen

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Re: Spring Time PSI
« Reply #3 on: March 30, 2007, 07:06:11 pm »
did you check the cold tire pressure or after you drove it? vechile tire pressure is based on cold pressure reading. To what Spock said  if  you started with 35PSI cold and then measured it after a run on the highway the PSI reading would be higher.. I don't think ambient outside temperature could generate that much of a difference    
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Offline RunsinLight

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Re: Spring Time PSI
« Reply #4 on: March 30, 2007, 07:07:59 pm »
Quote from: Allen on March 30, 2007, 07:06:11 pm
did you check the cold tire pressure or after you drove it?

Its been about 3 hours since I drove it
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Offline citydude

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Re: Spring Time PSI
« Reply #5 on: March 30, 2007, 07:26:02 pm »
I always check mine after the car's been parked overnight to let them cool down, then adjust to the recommended pressure.

Citydude
« Last Edit: March 30, 2007, 07:30:12 pm by citydude »
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Offline mmret

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Re: Spring Time PSI
« Reply #6 on: March 30, 2007, 07:51:10 pm »
T is in Kelvins, P is in Pascals
1 pascal = 0.000145037738 pounds per square inch

Now, for a temperature difference of 30 degrees say, from -15 to 15 celcius (258K to 288K), you're looking at a pressure difference of

288/258 = 1.116 or 11.6%.

If you set 35PSI @ -15 then you would have 39 PSI at +15.

Better to have more pressure than less I guess...? ???

Still, given that its unlikely to be minus 15 in most places until next winter, I would guess you should target 35 PSI @ -5 degrees or something. *shrug*
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Offline airbalancer

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Re: Spring Time PSI
« Reply #7 on: March 31, 2007, 08:19:45 am »
Quote from: mmret on March 30, 2007, 07:51:10 pm
T is in Kelvins, P is in Pascals
1 pascal = 0.000145037738 pounds per square inch

Now, for a temperature difference of 30 degrees say, from -15 to 15 celcius (258K to 288K), you're looking at a pressure difference of

288/258 = 1.116 or 11.6%.

If you set 35PSI @ -15 then you would have 39 PSI at +15.

Better to have more pressure than less I guess...? ???

Still, given that its unlikely to be minus 15 in most places until next winter, I would guess you should target 35 PSI @ -5 degrees or something. *shrug*

ouch :P
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Offline safristi

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Re: Spring Time PSI
« Reply #8 on: March 31, 2007, 11:10:56 am »
 ONLY PV=Rts RUN 39 lbs in their TYRES........Gotta loose tooth ya want shaken OUT..... ::) ??? 8)
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Offline cparsons

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Re: Spring Time PSI
« Reply #9 on: April 17, 2007, 07:13:00 pm »
I agree, 39psi has got to give you pretty stiff ride!  The 17s on the G6 GT only call for 30psi.  Gas mileage should be good though!
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Offline tortoise

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Re: Spring Time PSI
« Reply #10 on: April 17, 2007, 10:45:54 pm »
Tire wear, not so much!
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Offline safristi

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Re: Spring Time PSI
« Reply #11 on: April 19, 2007, 05:40:47 pm »
Centre Parting effect if too HI...... :cp2: :cp2:. rubber Police.... :rofl:
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Offline Craig

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Re: Spring Time PSI
« Reply #12 on: April 19, 2007, 06:44:01 pm »
My car came with 45/45/45/40 psi in the tires.  Clearly, Acura dealers know what they are doing, so I won't change it.




psi-ch


Took them all down to 37, just for the hell of it.
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Offline mmret

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Re: Spring Time PSI
« Reply #13 on: April 20, 2007, 10:37:39 pm »
Quote from: Craig on April 19, 2007, 06:44:01 pm
My car came with 45/45/45/40 psi in the tires.  Clearly, Acura dealers know what they are doing, so I won't change it.




psi-ch


Took them all down to 37, just for the hell of it.

Hmm, thats pretty close to the max PSI of those MXM4s isn't it?
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