Tires needing air

[Will99]

I have a 2017 Legacy Sport 2.5 with the stock Goodyears. Why are they needing air on a weekly basis?

[ncted]

I have a 2017 Legacy Sport 2.5 with the stock Goodyears. Why are they needing air on a weekly basis?

 

I definitely have to monitor the Goodyears on my Legacy way more than any car I've owned in a long time. Even with the stupid Nitrogen service that came with them from the dealer, I have to top mine off every week or two.

[laz]

2018 with Goodyear’s. Only time one went low was because of a nail. I live in Florida so we don’t have big changes in weather.

[ammcinnis]

Why are they needing air on a weekly basis?

 

1. Puncture (nail, etc.)
   
2. Schrader valve not sealing (body or core)
   
3. Tire bead not sealing
   
4. Porous wheel casting
   
5. Defective tire
   
6. Curb/pothole hit
   
7. Seasonal temperature drop (~1 psi for each 10 degrees F)
   
8. Your measurement technique needs work (i.e. is allowing air to escape)
   

A tire shop can probably find and fix it for you. They do this for a living.

[AWDFTW]

I have a 2017 Legacy Sport 2.5 with the stock Goodyears. Why are they needing air on a weekly basis?

 

Because they are leaking?

[TwoTone]

Because they are leaking?

 

I have to say I was wondering how someone comes on a forum to ask such a basic question.

[tornichoe]

I have to say I was wondering how someone comes on a forum to ask such a basic question.

 

You have to learn from somewhere!

[YeuEmMaiMai]

take it to discount and have them check all tires for leaks.

[ncted]

I lose at least one PSI per week on all four tires. Sounds like others aren't experiencing the same thing with their Goodyears?

[TwoTone]

I lose at least one PSI per week on all four tires. Sounds like others aren't experiencing the same thing with their Goodyears?

 

I doubt the gauge you have is that accurate.

[IcEWoLF]

I dumped the LS2 in a month and got the contis DWS06 and no issues.

[ncted]

I doubt the gauge you have is that accurate.

 

That is an oddly cynical response. I'm measuring Pounds per Square Inch, not Pascals after all. Don't most tire gauges (in the US anyway) measure in at least that increment?

 

Anyway, I check using the integrated TPMS readout on the info screen in the gauge cluster every work day when I get in the car to drive home. I'd say there is a problem with the TPMS system, but the Discount Tire I use for air check/fill always agrees that I am down a few PSI from where I should be.

 

FWIW: I do have a decent Mopar tire pressure gauge I got back when I owned a Jeep and they included them in the toolkit that came with the vehicle. It clearly measures in PSI.

[rec630]

I definitely have to monitor the Goodyears on my Legacy way more than any car I've owned in a long time. Even with the stupid Nitrogen service that came with them from the dealer, I have to top mine off every week or two.

Ditto (without the Nitrogen service)

 

eta: it may not be every week, but certainly a lot more than over the last 10 years when I have run different Goodyears or Contis.

[YeuEmMaiMai]

I roll by Discount once a week for a check, anything abnormal I goes right in.

[balbrec2]

I think the Nitrogen service is pure marketing bs.

Regular old air is already 78% nitrogen. What are you really

gaining?

[waldguy]

My LS2s hold air as well as any. No increased checking needed.

 

Only exception - a screw. Fixed. Good to go.

[tornichoe]

What are you really gaining?

 

You are gaining 21% more N2 instead of the O2 molecules that are smaller. How much smaller, "A nitrogen molecule measures roughly 300 picometers while an oxygen molecule measures 292 picometers. That's a 2.6% difference in size."

 

Real world practical scenario impact, probably minimal. On a new tire inflated the first time, you obviously got 21% o2 molecules, After those escaped and you filled up air again, you now have 21% of 02 of the 21% you lost. Do that a few times, and you should have mostly Nitrogen.

The loss of pressure you have in your tires week over week from escaping molecules should be minimal compared to the temperature differences of your driving conditions.

 

I can say this, when I air up my bicycle tires with co2 cartridges, I loose pressure much sooner than if I just pumped with a floor pump. Molecule size is a real thing and at a volume of just 700cc that molecule size is much more noticeable.

[ammcinnis]

What are you really gaining?

True answer: Bottled nitrogen is guaranteed to be dry, with ~0 water vapor content. Shop air typically contains a substantial amount of moisture unless the system is well filtered and properly maintained. Water vapor in a tire can condense (or even freeze) at cold temperatures, which will affect tire pressures. That said, for tire inflation there is no practical difference between pure nitrogen vs. dry air.

[ncted]

I think the Nitrogen service is pure marketing bs.

Regular old air is already 78% nitrogen. What are you really

gaining?

 

Agree 100%

[crudzinskas]

https://www.arpnjournals.com/jeas/research_papers/rp_2015/jeas_0615_2109.pdf

 

This debate of air vs pure nitrogen in tires comes down to a simple diffusivity/permeability problem that your average chemical engineering student should be able to calculate. Here is a nice paper that settles the debate. Air diffuses over 2 times as quickly as pure nitrogen through a tire!

 

Wow a huge difference, right!? In practice, no. This is basically the difference between losing 0.5 psi per month with air compared to 0.25 psi with nitrogen. Now if tires lost 1 psi every day and that was just an accepted way of how tires worked, nitrogen would be a bigger deal. For example, instead of having to fill your tire every 2 days, you might have to do it only every 4 days. Since on a well sealed tire you might have to add air only every month or two (at least in my experience), Nitrogen doesn't make a substantial enough difference to justify paying any money for it.

 

And for those who spend the time to think about whether or not to put in air or nitrogen, you are probably the type of person who checks their air pressure regularly, so might as well just use air

[ncted]

Well, either way, the Nitrogen in my tires comes out at a less than ideal rate. I am down a pound as of this morning, but it was really cold, so I will check again before I leave today.

[BobbyR]

I understand the molecular size explanation and how the smaller O2 molecules are supposed to pass more easily through the tire wall but I really doubt that this is what is actually going on. The more likely explanation is the water content of normal air results in more pressure variation with temperature and, even more likely, nitrogen fill is just hype, doesn't really make any difference (my experience) and is pretty much a waste of money.

JMO.

[Brisvegas]

even more likely, nitrogen fill is just hype, doesn't really make any difference (my experience) and is pretty much a waste of money.

 

True Dat

[08SpecB_DE]

You are going to drive yourself crazy over 1 psi difference from one day to the next. Has one tire ever gone 5-10 psi less than the others or is 1 tire in particular constantly losing pressure while others maintain? Do you have metal tpms sensors? They are known to corrode and leak ever so slightly. Spray a soapy solution on and around the sensor to see if it's leaking. Aluminum wheels can corrode around the beads or maybe you have a tiny pinhole leak.

[ncted]

You are going to drive yourself crazy over 1 psi difference from one day to the next. Has one tire ever gone 5-10 psi less than the others or is 1 tire in particular constantly losing pressure while others maintain? Do you have metal tpms sensors? They are known to corrode and leak ever so slightly. Spray a soapy solution on and around the sensor to see if it's leaking. Aluminum wheels can corrode around the beads or maybe you have a tiny pinhole leak.

 

If you're reply is meant for me, thanks. I am not going crazy yet, but I am having to pay more attention than I am used to with previous cars. No idea what kind of TPMS sensors I have. Car has ~7k miles now, so I would hope no corrosion is present yet. If there are any leaks, they are present in every wheel or tire or whatever. It isn't that big a deal, especially since I discovered Sheetz has free air. I just stop by once a week and top off. If it gets worse, or new tires have the same or worse problem, I'll probably investigate more. I am going to mention it the next time I take it in for service, in case it does get worse, so there is a record once the warranty expires.