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Air in tires

Discussion in 'Wheels & Tires' started by mlieberman, Oct 1, 2009.

    mlieberman guest

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    I have a 2010 528i. I just had a tire go low twice in one week. The dealer did not find a leak and said all the tires were low. They claimed that the tires will require air monthly. I found that "unusual." Is this typical or were they lazy?
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    eam3

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    I think it's normal for tires to lose air over time but I have never seen it to the point that they require air on a monthly basis. Did you actually check the pressure? How low did they go? I know that radical temperature changes always cause the sensors in my 5 to indicate that at least one of the tires is low. I'll check the pressures and there's nothing wrong so I'll reset the TPM.
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    John in VA

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    I know nothing about how finicky tire pressure monitors might be, but ambient temp changes can certainly affect your tire pressures. Nights are ~30° cooler this week vs, last here in northern VA.

    From Tire Rack:

    Since air is a gas, it expands when heated and contracts when cooled. In most parts of North America, this makes fall and early winter months the most critical times to check inflation pressures...days are getting shorter...ambient temperatures are getting colder...and your tires' inflation pressure is going down!

    The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower).

    In most parts of North America, the difference between average summer and winter temperatures is about -50° Fahrenheit...which results in a potential loss of about 5 psi as winter's temperatures set in. And a 5 psi loss is enough to sacrifice handling, traction, and durability!

    Additionally, the difference between cold nighttime temperatures and hot daytime temperatures in most parts of the country is about 20° Fahrenheit. This means that after setting tire pressures first thing in the morning, the vehicle's tire pressures will be almost 2 psi higher when measured in the afternoon (if the vehicle was parked in the shade). While that is expected, the problem is when you set your vehicle's tire pressures in the heat of the day, their cold pressures will probably be 2 psi low the following morning.

    And finally, if the vehicle is parked in the sun, the sun's radiant heat will artificially and temporarily increase tire pressures.

    We put some of these theories to the test at the Tire Rack. First, we mounted two tires on wheels. We let them sit overnight to equalize and stabilize their temperatures and pressures. The following morning we set them both to 35 psi. One tire and wheel was placed in the shade while the other was placed directly in the sun. We then monitored the ambient temperatures, tire temperatures and tire pressures through the day. As the day's temperatures went from 67° to 85° Fahrenheit, the tire that was kept in the shade went from our starting pressure of 35 psi to a high of 36.5 psi. The tire that was placed in the sun and subject to the increase in ambient temperature plus the sun's radiant heat went from our starting pressure of 35 psi to a high of 40 psi. In both cases, if we had set our tire pressures in the afternoon under the conditions of our evaluation, they would have been between 2 and 5 psi low the following morning.

    M3Driver guest

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    There are many varying opinions on nitrogen in tires but I have been running it in my M3 and X3 for over a year now. Those temperature swings are one of the reasons I changed. That and the fact that BMW engineers finally gave it the "Ja it' gutes s und wir genehmigen" (better late than never I guess). Now my local dealer has the setup to do do. You might check into that.
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    CRKrieger

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    Nitrogen in tires is pointless for a number of reasons I have elaborated before; mostly, that it is a gas and all gases behave according to Boyles' and Charles' laws. That's not an opinion; it's a fact. Unless it is completely free (and they're outta air), don't even bother.

    mlieberman guest

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    Tire Pressure

    Thanks for all the responses. These are run flat Dunlaps, 18". The car has only 2000 miles. I live is So. California so the temperature change is nominal although both times the sensor indicated low tire pressure in only one tire and in the morning when it is coolest - about 55F. I only filled the tire indicated by the sensor (at 6 am and dark so am unsure of exactly how low) and did not check the others. The dealer filled the other tires. I do not use nitrogen, just plain air that is already 78% N.

    I just think it odd that one tire went low twice in a week. I'll keep up the status if (or when) I have another incident.

    mlieberman guest

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    Thanks for the detailed response. So my understanding would be that my problem might be due to the sensitivity of the sensor system. I would think that the manufacturer rated pressure is optimal enough to not set off the sensor, but might vary from car to car. Hmm, how sensitive are the new BMW's?

    Since you are kind enough not to plug your serviceon this board, I will. I have purchased from Tire Rack for my old M3 and the web site easy to navigate, prices competitive and fast shipping.
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    eam3

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    The TPM on my 5 is hyper sensitive, if we have a (typical south Florida) hot day and it rains in the evening, therefore bringing the temperature down into the 70s, it's a 50/50 chance that I'll get a warning the next day. I have it on my E46 but it has yet to give me a warning but I check the pressures every now and then and they're ok. For whatever reason it's not as sensitive as the 5.

    M3Driver guest

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    Thanks for the science lesson. However it has worked for me.

    Cheers...
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    CRKrieger

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    "Worked" implies that nitrogen did something that air didn't - which is incorrect. What has 'worked' is that your tires have functioned properly regardless of what gas is inside them.

    The OP may have a slow leak - which nitrogen won't fix.

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