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Registered 2010 SLK300
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Discussion Starter #1
I know tire pressure should be checked "cold".

but should there be any adjustment for ambient temperature?

manual says front 32psi rear 35psi

I set the pressure correctly at a colder ambient and looking at the dash pressure reading ( after driving 100 yards) fronts at 38 and rear at 40. ambient was about 20F higher from when I set them.
 

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Banned
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7,812 Posts
If you check tyres warm they will always be higher. I think the label inside the petrol flaps tells you by how much.

Just looked + 4 psi
 

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Premium Member
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2,421 Posts
I know tire pressure should be checked "cold".

but should there be any adjustment for ambient temperature?

manual says front 32psi rear 35psi

I set the pressure correctly at a colder ambient and looking at the dash pressure reading ( after driving 100 yards) fronts at 38 and rear at 40. ambient was about 20F higher from when I set them.
bobl, "cold" is "ambient". How much time had elapsed from your setting the pressure 'til you drove "100yds" and the ambient temp was 20* higher? When I check and adjust t/p(as needed), I do it just before I start my drive. Also, since apparently you have TPMS, did you compare the dash pressure reading to whatever gauge you used to set the pressure?
 

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is nitrogren bettter than regular air since race cars use this?
Is it better? Well, if you have easy access to it, it seems to be, but since it isn't available from, say, your home compressor, imo, it isn't worth "switching".
 

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Premium Member 2006 SLK350
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6,796 Posts
PV=nRT
as Temp increases so does Pressure...whether it's the air you're pumping into them (and the compressed air off a hose will be slightly warmer) or after you've warmed them up a bit (or a lot)
 

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Premium Member
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PV=nRT
as Temp increases so does Pressure...whether it's the air you're pumping into them (and the compressed air off a hose will be slightly warmer) or after you've warmed them up a bit (or a lot)
JJ, if that's aimed at my response, exactly :tu: That's why I suggested checking, and adjusting if necessary, just before the driving starts.

I take it you've gotten Kismet out of hibernation :Beer:
 

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Sadly Gregg has passed away
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PV=nRT
as Temp increases so does Pressure...whether it's the air you're pumping into them (and the compressed air off a hose will be slightly warmer) or after you've warmed them up a bit (or a lot)
You gotta love a guy who knows his math and isn't afraid to use it! Atta Boy John!:tu:
 

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Registered 2010 SLK300
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624 Posts
Discussion Starter #9
bobl, "cold" is "ambient". How much time had elapsed from your setting the pressure 'til you drove "100yds" and the ambient temp was 20* higher? When I check and adjust t/p(as needed), I do it just before I start my drive. Also, since apparently you have TPMS, did you compare the dash pressure reading to whatever gauge you used to set the pressure?
the tpms pressure was about the same (maybe 1 psi higher) the day i set the pressure and i drove the same distance,
it was several days days later i noticed the increase at about the same distance
 

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Registered 2010 SLK300
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624 Posts
Discussion Starter #10
PV=nRT
as Temp increases so does Pressure...whether it's the air you're pumping into them (and the compressed air off a hose will be slightly warmer) or after you've warmed them up a bit (or a lot)
i understand that. an increase of 5 psi over a 20F increase in temp seems a lot. the pressure i saw seem to be what i see after driving an hour. i often check the pressure using theTPMS on a trip
 
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