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    Stupid question I know, but it's plaguing me....

    Okay, daft question coming.

    Just want to get my tyre pressures correct and it's the manuals fault. They say the pressure should be measured at an ambient 20*C. I know the pressures increase as the temperature rises so...

    Now I'm obviously not going to wait until it warms up as it was only 15*C today. So, simple enough question albeit daft and perhaps I'm taking this too seriously, but what would be the pressure loss of pressure for the 5*C difference. If that makes sense. I mean if the pressure in the rear tyre was 40lb/in2 as 15*C then the pressure would be higher at 20*C.

    Re: Stupid question I know, but it's plaguing me....

    You shoulda got the TPMS system. It does the math for you.

    The secondary TPMS display (forget now what it is called, but it is the instrument panel display mode which is only enabled when the car is stationary) shows you the difference between the current actual tire pressure and the recommended pressure at the tire's current temperature. So you just add or release air until the instrument panel pressure difference reading gets to be zero.

    The shorter answer to your question is that tire pressure changes by 0,1 bar per 10* Celsius (equivalent to about 1 psi per 12* Fahrenheit).

    Re: Stupid question I know, but it's plaguing me....

    Only one way to find out - check it! You must have gotten the little tire pressure checker for free when you got the car.....

    Re: Stupid question I know, but it's plaguing me..

    Yeah, if I had my time again I'd probably get TPMS as it sounds perfect for such situations. So, the 5*C difference is approximately 0.5psi which is helpful, thank you.

    As for getting a pressure gauge, you gotta be kidding. Unless there is one provided as standard with the car. I do have an electronic one though.

    Re: Stupid question I know, but it's plaguing me....

    Hello ResB,

    That is an excellent question, to which there are many many answers! Here in winter it may be -35C, so one has to inflate the tires to those standard values. Ideally, if the weather temps were resaonably stable for a month, one would take the average temperature fro an average day, say the avergae of the high of 22C and 14 low, and ste them at standard when the temps were 18C. Then you would be clse to correct most of the time.

    Here in Saskatoon, I set the tires once a amonths, based on the cliamtic means.

    For urban/suburban driving of shortsi distances, and modest speeds, that is Ok. However, if you were to head off on your favourite road for a 200 mile high speed jaunt that is not it: you should set the tires to standatd pressure for the high temps expected on that day before you leave. That being said, if you were to stop for gas after an exptended 100mph cruise for a few miles of your 200mile trip, the tire pressures would be circa 3-4 lb/in*2 high, and the ride would have been noticeably rough as you drove in to the gas station roads at low speed. Providing there was a service station at the end of your 200 mile jaunt, the ride and handling would be optimzed if you bled off some pressure to the standard. ...they would need to be increased at the end of the jaunt to maintain standard.

    Personally, and to improve the ride and impacts to the car and me, I run 4-6 ponds low all the time for daily suburban driving.......and ensure they are set to standard for any high speed jaunting. I have never ever noticed any uneven tire wear on the NSX or the Carrera in eyars of motoing and various tires. Such tire pressures changes are equivalent to moving your care from sport-springs to standard, and is very useful.

    My 997 3.6L-PASM with the firmer springs is then much nicer daily, effectively back to standard spring rates when I am no where NEAR the 997's peformance potential.......

    Omn track days, the instructors will bleed off prossure as the car and you get to higher and higher speeds, so the optimum is achieved on the correct and standard prossures.

    One note of warning, some car handbooks give higher standard prossures for extended fast driving; my NSX book say that the standard cold proessure are also OK for high speed, and not to bleed them in the midst og fast driving jaunts.

    So--------some care is needed, and some experimentation---also talking to some race-day Porsche drivers/instructors who know what they are doing, and know ehat the Porsche handbook REALLy means.

    Use care, and do not be afraid to run -4 to -6 ibs/in*2 for daily non-extended high speed stuff.

    Cheers

    KiwiCanuck
    taes....

    Re: Stupid question I know, but it's plaguing me..

    Wow, thanks for taking the time to post. Ask and ye shall find.

     
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