The tire pressure can change not only seasonal, but from hour to hour and day to day depending on ambient temperature.
I just found an article about NASCAR and it appears NASCAR teams run approximately 50 PSI nitrogen in their tires and they run at about 200*.
They use nitrogen because it has a more consistent temp-pressure relationship than moisture-laden air. At the extremes they run at, air is too inconsistent even hour-by-hour. They found it makes a big difference in predicting and tuning the tires for track conditions and maintaining traction. Those tires are specifically built for NASCAR, they use different designs based on the track type, and have less in common with the tires on your car than you think. They are designed for phenomenal traction at high speeds and tend to wear out before the first tank of gas is drained. You cannot use them in comparison to your standard 50,000 mile all-weather radials. That’s just ludicrous.
They run about 50 psi to maintain the correct contact patch with the incredible amounts of down-force the car body produces to let those cars turn left at around 175 mph. At speed, they ‘weigh’ more than an SUV.
I wasn’t comparing my tires to the ones used on NASCAR vehicles. My tires are not run at 175-200 mph and if they were capable of running under those conditions my 70K mile tires would take a significant beating as well and would run nowhere near 70K miles regardless of whether they had 30 PSI or 50 PSI. Actually the ambient temperature will have about the same affect on nitrogen as it does air.
On the Ford Explorer, Ford also revised the original 26 PSI tire rating to 30 PSI.
Heat build-up in tires is due to friction between road and rubber. The gas in the tires absorbs that heat, but has no place to transfer it. The gas expands as it heats, changing the dynamics of the tire. The manufacturers take that into account when they set the vehicle’s tire pressure recommendations. Ford changed that spec due more to marketing and the Firestone debacle than anything else. A higher set pressure means that maybe more tires will be less prone to being under-inflated by negligent owners. Under-inflation is more dangerous than over-inflation. But the change is only 4 psi, not the 14 psi you’re recommending.
NASCAR and Formula One use nitrogen in the tires because, at the extremes they operate at, the purified gas has a very consistent rate of expansion. Compressed air will vary rates of expansion based on the variety of gases and vapors in the air, like moisture levels, pollutants, sulfides, nitrides, and other things, which can change hour-by-hour. When racing at those levels, a change in 1/2 psi can shave as much as a second off your lap time. Nitrogen allows then to predict better how the tire will react given the conditions on track day. A much better option that carrying a gas spectrum analyzer and having a team of scientists constantly sampling the compressed air to get the same predictability.
However, this issue doesn’t work the same with ordinary street tires. It has been studied, and the same benefit doesn’t translate to street tires. Nitrogen in street tires only benefits the tire store, not the car owner. Over the many years a typical tire is in service, they haven’t yet seen a substantial benefit to using nitrogen over air for the life of the tire except to the tire stores that get an up-sale any time they service a nitrogen-filled tire.
The biggest claim is that nitrogen in tires saves fuel. This is based on the belief that nitrogen ‘leeches’ out of tires slower than air. But, nitrogen still leeches, so failure to monitor the tire pressure wastes more fuel than simply using nitrogen. Keeping tires properly inflated, with air or nitrogen, gives you the same fuel mileage benefit. Read the Consumer Reports study on it yourself. http://news.consumerreports.org/cars/2007/10/tires-nitrogen-.html
The other claim is that oxygen attacks and weakens rubber over time. The manufacturers have already taken this into account, and air won’t weaken a tire enough to make it unsafe from the inside faster than the outside will be attacked by air, UV and other environmental effects. Another article: http://www.associatedcontent.com/article/7897600/nitrogen_vs_air_what_is_best_for_your.html?cat=27
Waste your money on nitrogen if you wish. It is your money, and someone else’s vacation fund.
I don’t use nitrogen in my tires. I was just stating that at ambient temperatures the PSI variation is about the same as air contrary to what many people believe.
Wow, just wow: More incorrect information!
Let’s followup on the one I started: Sidewall Pressure!
First, there is a government regulation that requires that there be a number on the sidewall of a tire, but the regulation does not specify how that number is to be derived. Ergo, no government test!
Is there an industry test? No.
So how does a tire manufacturer decide what pressure to put on the sidewall? Well, there is load vs pressure standard published by tire standardizing organizations. It is the source for all the loads written on the sidewall. On my web site, I explain about load tables:
http://www.barrystiretech.com/loadtables.html
I also explain about the “notes on page 1-34”.
THAT is the source of what is written on the sidewall of the tire. Notice there is no testing involved or implied - unlike the table where the tire is required to handle the load listed at the pressure specified. Also notice that there are no guidelines as to what pressures is to be used when. It appears to be entirely up to the tire manufacturer - and indeed it is! They can use any of those pressures listed and they do NOT have to test, they do not have to justify, and they do not have to explain. It is entirely arbitrary. I know, I used to be the guy that did that.
That is why I say that anyone who points to the sidewall pressure has having any consistent meaning just doesn’t understand how tires work.
Alternatively, the pressure specified on the vehicle tire placard has a fairly consistent derivation (it starts with the tire load table!) and a ton of vehicle testing behind it. You can disagree with what the placard says, but if you point to that - refer to that - derive some scheme that uses that as a base, you will NOT be referring to something that is arbitrary.
And while I am at it: Ford / Firestone? Folks are emphasizing the inflation pressure too much. It was a small contributor to the situation I explain that here:
http://www.barrystiretech.com/fordfirestone.html
And heat buildup in a tire? Mostly due to the internal friction (hysteresis) within the tire components, not the friction between the tire and the road surface. It is this friction that also accounts for a tire’s rolling resistance.
The link below provides a table showing the affects of temperature on pressure using different gases.