14

How much air does a tire typically lose each month?

Do nitrogen-filled tires actually lose less air (well, nitrogen) each month? If so, what's normal for them?

According to a tire store manager I spoke with, a tire will lose about 2 PSI each month, whether filled with air or nitrogen. Does this sounds about right?

From my small sample size (the one vehicle I brought to him), he was right on the money. The tires were all 9 PSI low, and I hadn't checked them in about 4-5 months. (The spare was about 20 PSI low!)

If he is correct, and this is typical, we all should be adding air every month, as even a 2 PSI difference is significant.

  • Four car tires on a boat trailer parked up since 2003 (14 years) trailer on blocks - wheels clear of ground in a farm shed, result three tires flat but the fourth seems to have mostly full pressure, - will measure this pressure, no air has even been put into these tires in the above period, (wheel nuts were seized back in 2003 so hub was removed then less the bearing to remove wheel), this must be a world record! – hughtc Jul 14 '17 at 10:23
10

The tire store manager is pretty much on the money. A better way to say it, though, might be:

A normal tire can lose up to 2 psi a month.

Why is this important? Every tire/wheel combo is going to be different in the rate at which they lose air pressure. There are several ways (besides a puncture) a tire can lose air pressure. Those might include a bad valve stem seal, valve core issues, bead seal, or even a bad/damaged wheel. Some tire/wheels may never lose air pressure or may lose it at such a slow rate it is fairly imperceptible.

As far as using nitrogen goes, a Google Search turned up this quote:

First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings.

Remember, though, the air we breath is about typically 78% nitrogen and 21% oxygen (and 1% of other gases). Which means most of the gas we put into our tires normally is nitrogen ... if the above quote is true, it's mainly the oxygen which is escaping through the tire. Having nitrogen in your tires means if you want it to stay as such, you need to check and refill using nitrogen. This may pose an issue of travelling to your local tire shop to get the pressure checked, unless you have a portable source of nitrogen lying around.

With all this said, the most important thing you could do is to check your tires on a monthly basis to ensure proper pressure resides inside. This will keep you, your passengers, and vehicle safe from tire failure due to under-inflation.

  • 2
    So if we keep filling the tire with 78% Nitrogen and 21% oxygen, and only the oxygen escapes, theoretically the percentage of Nitrogen to oxygen increases asymptotically until it gets 99.9999% nitrogen. Meaning every time we refill a tire, it should be longer until the next time we need to refill than the last time we refilled! So the amount of air you lose per month actually decreases with the age of your tires. Pretty cool to think about... – dberm22 May 7 '15 at 20:13
  • 1
    @dberm22 - Well, that's the logical conclusion I get to as well, though I think the tire would wear out first in most cases '-) – Pᴀᴜʟsᴛᴇʀ2 May 7 '15 at 20:49
  • And it also sounds like a good method of obtaining extremely pure nitrogen :) – I have no idea what I'm doing Feb 3 '16 at 9:38
  • @IhavenoideawhatI'mdoing - Except for that pesky "1% other gasses" thing ... '-) – Pᴀᴜʟsᴛᴇʀ2 Feb 3 '16 at 11:18
  • I should add that on vehicles having active tire pressure monitoring system (TPMS) not based on ABS wheelspeed sensors but rather based on tire pressure sensors, checking the pressure on a monthly basis is not necessary. The TPMS will warn you about too low pressure. On passive ABS wheelspeed sensor based TPMS systems, you need to check tire pressures on a monthly basis, as it doesn't detect the case where pressure loss is equal in all tires. It only detects the case where one tire has lost more pressure than the others. – juhist Feb 5 '17 at 12:50
7

Normally a tire loses around 1-2 psi a month. However this figure is absolutely a generic statement. In real life, the figure depends upon various factors:

  1. How many miles/kms you drive daily?
  2. What is the condition of the road/tarmac that you generally drive on?
  3. What is your driving style? Aggresive or Defensive?
  4. Is there any puncture in your tires? (considering the tires are tubeless)

Now, coming to the specifics of the above points:

  1. If you drive your car daily for a considerable number of miles(~20 miles), then you may not see even 1psi drop in tire pressure over a month(if you dont have any puncture and considering all other scenarios to normal). However if you drive occassionally, then you may see a big drop(+2-4 psi) in tire pressure over a month. That explains why your spare showed so big drop (20psi) is tire pressure as you dont use the spare while on road.

  2. The broken the tarmac, the more drop in tire pressure is expected.

  3. If you drive sedately, avoiding sudden braking or acceleration or wheel spin, then you will not find big drop in tire pressure. On the contrary, an aggressive driving style will make your tires lose air pressure quite much and will also reduce the tire life.

  4. Lastly, quite obviously, if you have a puncture in your tubeless tire, you may see a good drop(~10+psi) in tire pressure. However, if the puncture is a tiny hole, then you may not see any difference if you drive your car daily for good distances.

That's my cent.

  • 3
    also, what is the recent temperature change is a factor, as described by Boyle's laws. If the temperature drops significantly, the tire air pressure will drop and vice versa. also (as i am a whitewater enthusiast), people rafting rivers who put on early in the morning will slightly underinflate their rafts knowing that the mid day sun will kick the pressure to be just right – amphibient May 7 '15 at 16:13
  • 2
    @SouravPurakayastha Thanks. That's great information. Why does driving a vehicle result in less tire pressure loss than not driving it (assuming driving on smooth surfaces)? – RockPaperLizard May 7 '15 at 21:05
  • @RockPaperLizard When the vehicle is being driven, the tire heats up, causing the air to expand and thus the pressure gets bumped up. The pressure stays in that 'bumped up' condition for a considerable time. – Sourav Purakayastha May 8 '15 at 6:22
  • @SouravPurakayastha Thanks Sourav. But wouldn't the pressure go right back down as the tires cool overnight? – RockPaperLizard May 8 '15 at 9:30
  • @RockPaperLizard Yes, the pressure will go back to the normal rating overnight, but think of a situation where your Merc C250's tires rise to 45 psi from the normal 40psi after driving and then they get back to 40psi overnight, and again you take it out the next day, the pressure again goes back to 45 psi...and the cycle continues. So, over a period of a week your average psi will hover around 40psi. However, on the contrary, if you keep your ride in your backyard for a week, the average psi will come down to around 38-39psi. – Sourav Purakayastha May 8 '15 at 13:27
3

I guess it is not a general rule that tires are lose some pressure every month. Temperature changes creates pressure difference most of the time.

Every 5.6 degree Celsius (10 F) equals 1 PSI. So, 32 PSI at hot summer day easily becomes 30 PSI when its get colder vice versa..

Note: Consider the temperature of the tire itself, ie. check them when they cold.

1

I disagree with an answer saying that tires normally lose 1-2 psi pressure per month. Yes, the upper limit (2 psi) can be okay, but the lower limit (1 psi) is definitely not correct.

Where I live, tires need to be swapped twice per year, as winter tires are mandatory during the winter. Typically, when I filled a tire to 2.3 bar for my 2011 Toyota Yaris when installing it, a year later (when it has been half a year in service and half a year in storage) the pressure is typically something like 1.9 bar. This is a difference of 0.4 bar, or 0.03 bar per month. In psi, it is approximately 0.5 psi per month.

The tires in an older 1989 Opel Vectra seemed to hold pressure much better: often times, when installing the tires (or actually the wheels), the pressure was correct and the tires needed no inflation. Based on this, the lower limit is indeed much, much lower than even 0.5 psi per month. However, once one winter tire had lost considerable amount of pressure during a year, but the remaining three had correct pressure. I don't know what caused this but the problem didn't repeat.

So, I would say that tires normally lose 0.1-2 psi pressure per month. I suspect the ultimate lower limit is caused by diffusion of air through the rubber. Nitrogen diffuses slower than oxygen, so nitrogen holds up pressure better. Remember, however, that about 80% of air is nitrogen. The possible 2 psi per month pressure losing is probably caused by a seal between the wheel and the tire that isn't completely airtight. If this seal is bad, I suspect nitrogen won't help at all.

Interestingly, bicycle tires lose pressure much faster, and high-pressure tires need to be filled approximately twice per month. I suspect this is caused by the fact that bicycle tires have less rubber so the air can diffuse through the rubber easily. Also the fact that bicycle tires have only part of the rubber (the inner tube) as an airtight seal probably plays a major role in this.

1

I really feel there is not an absolute rule for this. From my own personal experience, for the longest time I did not maintain my vehicle myself, I would never check or top of tires. From time to time the mechanic would top them up, but normally when I was having something large done.

Now I have started to do it all myself including checking pressure. Over the past 7 months, 1 tire has had to be topped up twice, needed to add about 4 psi each time. The other three tires lost nothing, were right on 34 psi as spec. I know for sure no one else filled this up. 0 psi drop in 7 months.

I travel 750km's a week on this vehicle.

My suspicion is that each tire will have different microscopic imperfections, same with rims, same with installation. I ponder whether removing and reinstalling a tire that regularly leaks a lot, would address the issue.

As I lost 8 psi in 7 months, my experience would be summed up as 1.x psi a month is reasonable.

If you are getting a couple of psi a week leaving you, its probably worth getting it looked at.

  • Assuming no nails, screws, or glass, you probably have a bead leak in that tire. – RockPaperLizard May 20 '17 at 4:07
-1

Depends on the tire. After 3 months, my Michelins had gone down by 3 psi, the cheap Chinese tire I had on went down by over double that.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.