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Way Off Topic

Discussion in 'General Discussion' started by Baywing, Sep 29, 2005.

  1. Baywing


    Feb 22, 2005
    CT USA
    Ok, this isn't really photography related....wait! Yes, I guess it can be, most of us use cars to get to locations to photograph, so maybe this does have some relevance after all.
    Why is it that we always have to add air to the tires? Have you ever taken any out? No, but about once every few months, you have to put more in! Where does it go? I thought that tires are supposed to hold air? No, I don't have any leaks, punctures or bad valves. I've noticed this with every vehicle I've owned and every set of tires. Soak them in a bucket (ok, a big bucket!) of water, you don't see any leaks.....so then, where does that air pressure go??????
  2. shudderbug2


    Mar 25, 2005
    Raleigh, NC
    Must be you....

    Because I've owned cars for years and never had that kind of problem unless it was leaking past the valve or something. With that said, Air pressure is related to temperature and will build up with heat. Hot days your tires will appear to have more air then on cold days. It's a matter of expanding and contracting molecules.

    Watch a NASCAR race sometimes as they set tire pressures low and then let them build up as the heat builds up. That's why some cars are set up for "long runs" and some for "short runs". They will make the tire pressure higher initially for a short run so the car handles better if they don't have many laps to run. If they have a lot of laps left they'll start the pressures lower so it will build up over time and be at the ideal pressure near the end of the race.

    Hope this helps!
  3. Air molecules slip by the valve, the junction between the tire and rim, even through the material the tire and wheel are made of.

    It is just a slow process, and depends on the material. You might note how a rubber helium filled balloon loses its shape in a few days, whereas a mylar balloon will last a week or more. But inevitably, those little gas molecules slip by.

    I have noticed some variability in this with the various vehicles (and their wheels) I have owned. I have also noticed that a vehicle that spends more time sitting won't lose pressure as quickly. Could be the action of rolling the wheel on the road helps the air escape.

    My current truck, a 2004 Toyota 4Runner has little pressure gauges in the valve stems that cause an indicator on the dash to light up if one of the tires is low on pressure. I find I have to top off the tires about every two or three months.

    The spare, which wasn't touched since new (early 2004) didn't lose enough air to cause this until a few weeks ago. Some few years after it was first filled.
  4. MontyDog


    Jan 30, 2005
    #1064 - You have an error in your SQL syntax;
  5. Baywing


    Feb 22, 2005
    CT USA
    Actually, I wasn't looking for an answer, as the answer is, as a tire rolls down the road, the sidewall flexes allowing a little air at a time to leak by the bead at the rim. Therefore, the more miles you drive, the more often you need to check your tires. Potholes and bumps add to the losses.
    Congrats to Beezle!
  6. Chris101


    Feb 2, 2005
    Very fun!
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