Well, I think it's been mentioned somewhere.

All tires are porous, allowing air to escape. It's a matter of degrees. It seems, you were lucky enough to get a really porous set.

Just for reference, when I had my flat tire the other week, I threw on a pair of my original wheels with the original tires. Once on the car they looked like they were at full pressure (no bulges like when a tire is low). At that's considering I hadn't touched them in some 18 months since I bought the new wheel and tires. Even the newer tires didn't need me to add air. The only reason I used my air compressor to pump in air was because I wanted to adjust the pressure to see if higher or lower was better for me.

Anyway... as a lazy person, 4 times in 6 months seems like a leak to me... albeit, a really slow one. But then again, one of the "Rules of the Road" (at least in Illinois) is checking the tires every week and inflating them as necessary.

So I'm thinking this would be classified as "normal."

 

especially when temps are dropping outside and you're using air (not nitrogen) pressure will drop. 1psi change per 10F ambient temp change.

 

I have aftermarket wheels and TPMS light is on the whole time. I just trained myself to ignore it.

 

Thats OK I couldn't either. You should see the errors after first pass. I gotta get a new keyboard. Or maybe new thumbs. these are really old.

 

I think filling tires with pure nitrogen is a way for tire shops to get more $$$ from your wallets. I find an 80/20 gas mix of nitrogen to oxygen, with a smattering of other gases in the mix work fine, and it's available free!

(for the uninformed, the atmosphere is already about 80 percent nitrogen, so you're paying only for a 20% increase in nitrogen when you pay for straight nitrogen fillups. And if the other 20% of gases leak out faster, the % of nitrogen constantly rises in your tires as you add more straight air and the other gases leak out.)

On the other hand for my bicycles I like straight co2, cartridges usually can be had in bulk for about $1 each, as I no longer can handle a bike pump and use 1 co2 cartridge per bike tire fillup. Heck, I'd even use my welding "gold gas" (mostly Argon, some CO2) mix if my tank was near wherever I was filling tires!

 

Some of the better dealers do it for free. While not perfect, it does slow down the seepage. That said, it is easier to stick with air, and check it OFTEN. Doesn't take long and is not that hard. Gets you looking at other things while you do it. Like tire wear, check the oil, brake fluid and filters.

 

The racing community from F1 on down have been using pure nitrogen in their tires for years because they value a very accurate tire pressure that lasts in the harshest road racing conditions.

Another good reason is water. In our tires with varying weather/temperature conditions water/humidity is a constant presence inside the tires. It can rust your rims as well as break down the rubber faster. Nitrogen dramatically reduces the amount of humidity inside your tires.

Using nitrogen from a tire shop can extend the time between top ups.

Having said that.

If you have pure nitrogen in your tires and then a few weeks later add regular air then the effect is ruined and you've just wasted your money. Kinda like adding water to beer. Just plain rude.

The only way I would recommend using nitrogen in tires are for owners who only check their tire pressure when the dealer does it every six months. It will raise the chances that your pressure will stay at the required PSI longer.

If on the other hand you are like most FitFreaks and check your air pressure every two weeks or when the temperature changes with the seasons or just because that front one looks a little off today....well regular air is the way to go.

For the OP: it is absolutely not normal for a tire to drop 5-10 PSI in a week unless a severe temperature change occurred. And it would affect all 4 tires evenly. Bumping your tire against something like a curb can let some air out. But jees... that would be a serious amount of jolt to break the seal of tire and rim.

If you have to top up your pressure more than 5PSI weekly on one tire...take it in and have it inspected. There is no magic fix available for that one. Sorry.

 

I'm afraid nitrogen passenger tire fills are a bit of a con. It's designed to capture customers, have them come back for tire fills so they can sell more services.

Normal air is 78% nitrogen. Unless they mount the tires in a nitrogen filled room with breathing helmets for the operators, the most they can hope for is a higher percentage of nitrogen achieved through a couple fill/release cycles. But not much higher. The claim of less corrosion/oxidation on the inside of the tire is a bit silly; since the outside of both the tire and wheel are still exposed to the elements (and normal air).

Consumer Reports did a piece on it and concluded it's a waste of time and money in passenger cars. I agree. You still have to check pressure regularly.

There is an advantage to pumping clean dry air in your tires avoiding mucking up the TPMS sensors/valves. I never saw an advantage to worrying about air quality other than this.

If you're concerned, get a small compressor to fill your tires at home. A small pancake tank compressor is about $85 and serves a lot of uses. The moisture will drop out of the air in the tank and drain through the bottom, or you can add an additional filter/water-trap for about $25.

 

unless you have 2 valves like some of the kosei wheels, i think it's impossible to fill with pure nitrogen if your car came with air in the tire.

 

Yup! Good investment I think. I have one of those... Very handy... and just keep the tank valve open when not in use... Checking regularly is the key! Just my take...

 

if you have rubber valve stems it's a good idea not to bend them too much in the winter time if you're in 0F temps... ive seen them crack. not enough to leak air as there's a brass valve inside, but if it cracks near the wheel it will leak.

 

I highly recommend Nitrogen filled tires...




To Formula 1 race teams.




I filled my tires with air about 4 months ago and they still have the same pressure as they did then. I guess my tire guy was a pro at sealing beads or something.

 

As an old tire engineer, let me assure you nitrogen has no practical use on the street. N2 has a lower expansion than O2 so pressure changes with changing tire temperatures on track are far greater wiktgh O2 but that's not true on the street. That means less pressure change with N2 than O2 on track and on track thats critical , but not on the street which sees nothing like the tire temps on track..
Nitrogen is a larger molecule than oxygen so it can permeate slower out thru the tire fabric and rubber matrix but both nitrogen and oxygen take so long to bleed thruogh the tire that it is not worthwhile to pay for nitrogen compared to free air.
Its a technical issue that has no worthwhile use on the street.
Next thing we';ll hear is adding water in the tires will make traction sooooo much better. Hey, it works with farm tractors. Just like N2 in GP Pirellis.

 

I too have had the TPS light come on recently. The problem turned to be my nice dial pressure gauge, with brass fittings. My pressure gauge was reading 4 to 5 psi low, so I was under filling the tires. Now I'm using an inexpensive Wal-Mart digital gauge that is much more accurate.

 

I wonder if anyone here actually reads a post before responding to it. Seems 75% of people see 1 or 2 words and go off on a tangent.

 

I can offer no scientific proof, but circumstantial evidence tells me that when I went from the dealer-applied 35 psi to a firmer 40 psi all around, I went (from one tank to the next) from 33.6 mpg to 41.2. I've done the math about twelve times, and I can't make it come out any other way.

 

likely your average for the vehicle is about 37mpg and the first tank was completely filled (resulting in a lower mpg number) and the second fill up wasn't up to the same spot (resulting in a higher number). I track all of my fill-ups and see this as a regular occurrence (one is either low or high, and the next is the opposite) This is why it is better to track mpg over the "long term" and not on a tank-by-tank basis. I suspect the next few fill-ups will show lower numbers (or a similar pattern)

(also, the on-board computer has a tendency to be off a little so manual recording of the odometer rating and gallons is more accurate)

Realistically, there's no way 5psi boosts you up 8mpg. I'm running 35psi and have ranged from mid 40's to high 20's in fuel economy based upon environment variables.

~SB

 

While we have lots of objective test data that shows mpg will increase with higher tire pressure (up to 45 psig), an increase of 25% in mpg is a bit unrealistic.

 

I agree w Specboy and Mahout. Get your ave. over the next few refills. 40psi is a bit high for my comfort zone. Might end up with center wear on your tires. Just me...

 

I agree that the MPG thing is probably a fluke. But I've run 40 psi in my Accord and Civic tires since 1986 (two different Accords and two different Civics), and have yet to see *any* sign of abnormal center tread wear on any tire I've owned, and that's a lot of tires (186,000 on Accord #1, 210,000 on Accord #2, 247,000 on Civic #1, and 200,000 on Civic #2). The manufacturer says 44 psi is the max pressure, so I take them at their word.