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Temperature Considerations when setting tire pressure

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by s1njin, Jan 20, 2011.

  1. s1njin

    s1njin New Member

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    Hey Gang,

    So I'm wondering how you guys figure out how much air to add or remove to hit your desired PSI when seasonal temperatures are concerned. I would imagine this is more of a concern for the 42/40 crowd than it would be for the 40/38 or 38/36 crowd, but it still applies.

    It seems to me that itd be easier to hit your target PSI in the winter when the temperature swings maybe 20 degrees. For me, I put a thermometer in the garage overnight and see what it reads in the AM. Its usually about 40 degrees. Knowing my temps at this time of the year go from 15-35, I'd use 30 as a target.

    So, my garage is 40, my target is 30, so I know I can add a extra pound of air.

    But, what happens in the summer? Garage might read 70, but black tires on black pavement in the parking lot when I head home from work - heck that could be over 110 degrees. How do you set your pressure in this case? Do you figure maybe 90 degree target, SUBTRACT 2 pounds from your goal psi? Seems I'd be running pretty flat in the AM but on target or above on the ride home.

    ????
     
    #1 s1njin, Jan 20, 2011
  2. Bob64

    Bob64 Sapphire of the Blue Sky

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    Uhh... the tires are built to tolerate a wide range of psi. Some of us run 60psi. No, the tire doesn't blow up when you go over 44. The max sidewall pressure is the maximum weight the tire can hold, going higher then the max sidewall pressure won't allow it to hold more weight , but can reduce its rolling resistance.

    Besides, you only need to worry about the "cold" pressure. You know what they say about putting air in tires right? Don't put air in tires when they've been driven? That's their way of preventing people from thinking the tire is "too full" when its warmed up after being driven. So measure the pressure when the tire is COLD in the mornings, and just set it then. Don't worry about compensating for temperatures that are generated during driving.
     
    #2 Bob64, Jan 20, 2011
  3. s1njin

    s1njin New Member

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    Sorry if I was unclear - I always set my pressure in the garage in the AM. That's why I put the temp gauge in the garage the night before - so I know where I'm setting the pressure.

    I was just worried that if I set my tires close to the max sidewall pressure when the car is 'cold' in the summer at 70 degrees, is it dangerous when I get back into the car after work after the car has been sitting in the parking lot and could be 110 degrees? That's 4 pounds of air differance due to the temp rise, which would concievably take me over max sidewall pressure.
     
    #3 s1njin, Jan 20, 2011
  4. qbee42

    qbee42 My other car is a boat

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    You were clear, and so was the reply. Tire pressures are stated as cold pressures. If you stay below the recommended maximum cold pressure you are fine. The recommended maximum includes headroom for pressure rise due to temperature.

    Tom
     
    #4 qbee42, Jan 20, 2011
  5. s1njin

    s1njin New Member

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    Thanks guys.
     
    #5 s1njin, Jan 20, 2011
  6. fuzzy1

    fuzzy1 Senior Member

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    I would also presume that includes margin for elevation change in the mountains. The difference between sea level and the high Colorado passes would about 5 to 6 psi (separate from temperature change), yet I've never seen any recommendation or facilities to release pressure on the way up and re-add it on the way down.

    But I do know from direct experience that when a dealership at about 6000 feet reduces the 'dangerously high pressure' in my highway-warmed tires down to 40 psi, then 36 hours later at sea level they will be underinflated.
     
    #6 fuzzy1, Jan 21, 2011
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