Acceptable tire psi loss per month?

[supton]

I swear, on my VW I've never had to put more than a couple of psi in, once a year, over several sets of tires. Maybe they weren't that good, but, pretty darn good--I eyeball them once a month, and they are never obviously low; and when I measure them every 2-3 months with a gauge they might have lost 2 or 3psi. Usually they just need topping off when I rotate summer and winter tires.

I aired up my truck tires for a trip at the begining of August, and just checked today. I put in 38psi back then. Today, the two fronts were down 4psi or so, one rear was down 8psi, and the other 13psi (down to 25psi!). One month! Ouch.

What's an ok amount to drop in a month? It's not that I can't add air once/week (well, more like every other, since stuff always comes up, and it'll be harder in winter), it's just that I've never had to stay on top of tires like this before. Seems to me the auto dealer isn't going to be able to do much here, since it's a very slow leak.

[Oh, and don't remind me, yes I have TPMS, and no, it didn't trigger anything last weekend when I last drove it. I don't think that one tire suddenly lost all its air in the last few days... Methinks it's time to disable it--what good is it?]

 

[The motor guy]

My tires don't lose any unless an extreme temperature swing. I used to check them once a month but it was just a waste of time so now I just look at them for anything abnormal.

 

[Errtt]

I dunno but I have 1 vehicle I have to add every month while the other two vehicles get a little air every few months or so.
http://forums.nasioc.com/forums/showthread.php?t=109351

 

[Colt45ws]

The fronts are normal, the rears are not, especially the 13 psi one. I would get that one checked.
Also, it depends on when you checked them. If you aired them up at the beginning of August after driving a couple of miles and today you checked them cold, you will see more variation. Main thing I look for is consistency. If all the tires are down 5psi, thats fine and Ill accept that. However, if three are down 5psi and one is down 20; I would be taking a closer look at that one.

 

[Falken]

1psi per month as per Tire Rack, assuming stable temps.

 

[DBMaster]

I check twice a month and rarely need to add more than 1-2 psi. Most of that is really due to temperature variation. I use a bicycle pump. I get a small bit of exercise and am at least putting DRY air into the tires. Have you ever seen how much water sprays out of your average gas station "air" hose?

I also pretty much always find out about nails or screws in tires this way. If one tire is more than a couple of psi lower than the rest I check it and, usually, find something stuck in it.

 

[Falken]

I keep a small electric tire pump that I got for 7$ on sale at Canadian Tire in a thick Ziploc bag in my spare tire well.

Works well and as mentioned, steer clear of wet air from some old compressor.

 

[DBMaster]

I use a large bore high end type bicycle pump (Avenir, in this case). I have tried the small compressors in the past and they seem to take a lot longer than 10-20 strokes form my manual pump.

My opinion would probably be different if I had those big balloon-like SUV tires. Low profile performance tires like mine don't contain that much air.

 

[supton]

It's a big tire, 255/70R18 IIRC. Makes the home compressor a worthwhile thing to have handy. I put air in while cold--well, whatever ambient is--but the tires were aired up in August so it was 70+, today it was barely 60 when I topped off.

Ok, will see what the dealer will do. They put the tires on, and maybe they'll deal with it, CPO and all. I'm a bit dubious, since they are a dealership and not a tire-ship. These are steel rims, not alloys, and they do have the TPMS sensors, not sure if that has any relevance.

Push come to shove I guess I could just buy snows and have a tire shop put them onto these rims, checking the rim etc; and have the all seasons put onto a different set of rims come spring.

 

[jhellwig]

The tpms has nothing to do with the tire looseing air. It just tells you when the pressure has dropped below a preset point.

Get some soapy water in a spray bottle and find the leak. You could have picked up some nails that dont leak very fast.

 

[Eddie]

1-1.5 PSIG PER MONTH

 

[Kestas]

Most of my psi maintenance comes more from temperature swings than from leaks.

Like DBMaster said, regular checks are a good way to determine if you have a nail in your tire, or are developing corrosion at the bead sealing surface.

 

[Kestas]

Originally Posted By: DBMaster
I get a small bit of exercise and am at least putting DRY air into the tires. Have you ever seen how much water sprays out of your average gas station "air" hose?

I disagree. Air in = air out, in both cases. Gas station compressor air doesn't somewhow concentrate the water from the air, nor does the bicycle pump somehow remove water from the air.

 

[Cardenio327]

Rule of thumb is: 1 psi per month for car & light truck; 2 psi per month for heavy truck tires.

Did they rebuild the TPMS sensors when the new tires were mounted? If your wheels have the sensors mounted behind the valve stems they should be rebuilt periodically. The rebuild kit will contain new o-rings, seals, cores, caps, stems, &c.

If you run without valve caps dust and water will etch the valve cores & stems, causing them to lose air slowly.

The tire that loses more air needs to be dismounted and checked carefully for punctures, torn bead, cut liner, corroded rim, &c.

 

[supton]

Brand new tires, about 3k in the five months I've owned t. I will take a look for a nail, but I think this tire took quite a bit air the first time I brought the psi up (dealer put in 33, but I've read of better life at 36, and I wanted better mpg too). No idea if they rebuilt the TPMS, but when the tires come off I plan to remove the sensors. I can't say I like the system in either of my vehicles, neither seem to be functional.

 

[147_Grain]

Originally Posted By: Cardenio327
Rule of thumb is: 1 psi per month for car & light truck; 2 psi per month for heavy truck tires.


Originally Posted By: Kestas
Most of my psi maintenance comes more from temperature swings than from leaks.

 

[user52165]

Originally Posted By: Kestas
Originally Posted By: DBMaster
I get a small bit of exercise and am at least putting DRY air into the tires. Have you ever seen how much water sprays out of your average gas station "air" hose?

I disagree. Air in = air out, in both cases. Gas station compressor air doesn't somewhow concentrate the water from the air, nor does the bicycle pump somehow remove water from the air.


You have obviously never owned an air compressor. Unless a water separator is used or the tank is emptied very often (probably daily for a high use item) thru the drain valve, water will collect in the tank and be transferred out with the air. This is one way air tools may be damaged unless oiled.

Even in a dry climate like San Diego, I still have to be very careful. The process is compressing the air will squeeze the water out of air. Takes much less time in high humidity air.

 

[JHZR2]

Originally Posted By: DBMaster
I use a large bore high end type bicycle pump (Avenir, in this case). I have tried the small compressors in the past and they seem to take a lot longer than 10-20 strokes form my manual pump.

My opinion would probably be different if I had those big balloon-like SUV tires. Low profile performance tires like mine don't contain that much air.


Me too. Far prefer a manual pump, and the cheapos pack easily for trips.

I think that temperature changes have as much to do with it as anything. If you top up in July at 88F and now it's 72F, pressure will change.

 

[DoiInthanon]

Originally Posted By: user52165
Originally Posted By: Kestas
Originally Posted By: DBMaster
I get a small bit of exercise and am at least putting DRY air into the tires. Have you ever seen how much water sprays out of your average gas station "air" hose?

I disagree. Air in = air out, in both cases. Gas station compressor air doesn't somewhow concentrate the water from the air, nor does the bicycle pump somehow remove water from the air.


You have obviously never owned an air compressor. Unless a water separator is used or the tank is emptied very often (probably daily for a high use item) thru the drain valve, water will collect in the tank and be transferred out with the air. This is one way air tools may be damaged unless oiled.

Even in a dry climate like San Diego, I still have to be very careful. The process is compressing the air will squeeze the water out of air. Takes much less time in high humidity air.
Everyone above is correct in my opinion.

Moisture in air is a function of psychometric properties and independent of the type of compressor.

Air tanks do need to be purged daily to eliminate accumulated water.

Often service station air systems, even if the tank is purged daily, will deliver water due to the configuration of the piping system. The system needs to be designed to drain water to collection devices for separation or purging.

More than you ever wanted to know - In engineered systems, lines are sloped where possible to allow gravity to collect the water in drip legs or separators. Prior to sandblasting or breathing the air, the procedure is to operate these devices to clear the water. Because of use in confined spaces, the air system is monitored for carbon monoxide, carbon dioxide, hydrocarbons, and other constituents as required. The limits can be very low. So low that diesel powered tanker trucks bringing fuel to the air plant have shut down the whole shipyard system from truck exhaust sucked into the air plant intake. Air intakes at forty feet above grade. Air samples were routinely taken on a random basis and run through a mass spec analysis to insure the process remained in control. I left that facilities job 35 years ago. Today, the systems are probably more flexible, safe, and efficient. Sorry for the tread jack.

 

[DanielinTheLions]

I would say that what I've observed is about 1 to 3 psi per month being normal in my vehicles. There's definitely something wrong with psi loss your seeing on the the rear tires. One common source of a very slow leak like that in my experience is the valve stems. Interestingly a guy once told me to put ATF in a tire that was leaking very slowly like that. I thought he was crazy but I tried it once on an old 96 dakata that I had very old tires and it worked. When I broke the tires down later the ATF was no where to be found. I guess it must have absorbed into the rubber and softened it up. I'm not sure I would recommend the ATF solution, or that I would use it on one of my current vehicles....I guess it depends on whether you like to experiment with crazy home brew fixes.