Spare tire. Most space saver spare tires recommend 60 PSI inflation.
This happens with my Insight every year when the temperature drops. It just happened a week or two ago. Each time I check all four and they’re all a pound or two below spec. When I pump them back up to the proper pressure the light goes out. Your issue is almost certainly due to a drop in pressure due to the temperature dropping.
I spent a little extra on a compressor where you can set the pressure and it will stop*. Easy way to make sure all tires have equal pressure.
- Bought after my last compressor started smoking and simultaneously finding out Pirelli tires can handle 130psi.
While I maintain that this happens every year when it gets cold, this turns out to be the car who cried wolf too many times. The rear passenger side tire was indeed low. I suspect a valve stem problem since the tires were rotated and checked last week when I got my oil changed. Since someone brought up filling them with nitrogen though, I have another question. I bought these tires in July and they *were *inflated with nitrogen. What are the implications of having three tires filled with nitrogen and one filled partially with generic air? I don’t know if the oil change place used nitrogen or not when they topped them off last week but I increased the 4th tire from 25 to 35 psi last night with plain old air. Is the pressure in that 4th tire just going to fluctuate more with temperature changes? When I get the valve stem repaired (assuming that’s the problem) should I ask the shop to deflate the tire completely and refill it with all Nitrogen?
You can, but I wouldn’t worry about it… or pay extra for it. Air is 78 percent nitrogen anyway, and it is unnecessary to fill your tires with nitrogen. Airplane tires, race car tires? Sure. Passenger vehicle? Waste of money.
This is repeated ad nauseum by tire shops and others, but it is simply not true. Nitrogen and atmospheric air both obey the ideal gas law to very high accuracy. For either gas, the pressure temperature relationship can be modeled as:
P[sub]2[/sub]/P[sub]1[/sub] = T[sub]2[/sub]/T[sub]1[/sub]
(always remember that pressures and temperatures must be expressed in absolute terms for this equation to work)
So whether your tire is filled with nitrogen or air, if your tire gauge says “32 psi” when the tire is at 70F, and you drop the temperature to 25F, your tire pressure gauge will now read “28 psi.” That’s a drop of more than ten percent, which may be enough for some TPM systems to trigger a warning (especially if you used an inaccurate gauge to set the pressure in the first place).
The one situation where nitrogen can make a difference is IF you have a tire that operates at very high temperatures, AND if there is any liquid water inside the tire at room temperature. Very high temperatures (>150F) are not encountered outside of racing applications, and liquid water isn’t likely to be a problem unless you’ve filled your tires with one of those little glovebox air compressors (the kind with no storage tank) on a very humid day. If you don’t have both of those factors (high operating temps + standing water in tire), the tire pressure-versus-temperature behavior will be almost identical regardless of whether you’ve used air or (dry) nitrogen.
Yeah, it’s a scam. If they’re racing slicks and you need the pressure to remain even during a hot lap it’s worth it, but otherwise it’s a waste of time.
I was under the impressing that filling tires with nitrogen was to reduce air loss through migrating through the tire wall. Either way, it’s a pretty minimal solution.
We put nitrogen in aircraft tires as pressures in them are a little more critical. Also nitrogen doesn’t support combustion which might be a factor in a hot brake situation. Even with aircraft, good old dry air was OK if nitrogen wasn’t available.
I surprised that no one has come up with the old ‘winter air’ joke…
Again, no temperature-versus-pressure difference between nitrogen and air.
This is the biggie. I don’t know about the small tires used on lightweight general aviation aircraft, but big commercial airliners fill their tires to around 200 psi. At that pressure, if the tire is filled with air the partial pressure of oxygen inside the tire is enough to be dangerous. See Mexicana Airlines Flight 940, which crashed in 1986 due to a tire that had been filled with air (instead of nitrogen). The tire caught on fire on the inside (due to an overheated brake) and built up enough pressure to explode before the thermal fuse (designed to release tire pressure in the event of an overtemp) could respond.
Car tires are only filled to ~35 psi; the partial pressure of oxygen inside the tire under these conditions isn’t really enough to constitute a major fire hazard.
Depends on the car and tire rated for it really. Mine’s over 40, I took this after reading the OP.
My sensor light had been coming on too and yes, it’s annoying as hell when you set the pressures with a gauge and it’s still indicating on the dash. I had the dealer replace them all (it was time) and we discussed where to set the onboard computer to register and it’s been perfect ever since. I can make minor setting changes via the dash but something bigger like that did need dealer input.
Agree with all said on nitrogen. It definately makes a difference for Ferraris on the track but with your standard passenger car it’s a gimmick.
Agreed. I think it’s valuable to let you know while travelling if a situation has developed but to actually measure, set and periodically check your pressures a gauge is far more accurate.
Yep, mine has no spare so it’s prudent to keep a real close eye on all tires for pressure, wear, damage, etc.
That’s interesting. I was reading all the tire stuff in my owners manual yesterday and it said never to use that stuff because it can mess up the TPMS.
Thanks everyone for all the great info. I’m off to get the tire repaired after work today.
As others have said, cold temps affect tires filled with nitrogen as well as ambient air. My Honda’s tires have nitrogen and every time the weather turns colder, the warning light comes on. It is not true as somebody posted that the sensor recognizes the difference in pressures and not the pressure itself. When this first happened to me, the guy at Honda said he could tell by the light which tire it was, but I had rotated the tires.
The problem with having nitrogen is that I have to go to the Honda dealer to fill the tires.
Things go flat in the cold. Playground balls are another good example. In the winter, if the car sends you that message, ignore it.
No, this is bad advice. As discussed in this tread, the light goes on for a reason. Air up your tires so you’re running at the recommended pressure.
Your first two sentences are absolutely correct. Your third sentence is absolutely terrible advice. Car tires need to be filled to rated gauge pressure, regardless of ambient temperature. If they are low - whether because they’ve been leaking, because it has become cold out, or because you drove from your home in Leadville, Colorado (elevation 10,152 feet, ambient pressure 10.1 psi ) to La Jolla, California (sea level, ambient pressure 14.7 psi), the sidewalls will flex more than they are designed to take; they will fatigue, and they will fail catastrophically.
There is another possible factor, phase change of any (humidity) in the air in the tire, once the temperature goes below freezing. Cold air holds less humidity and it can percipicate out into a solid.
It still has volume.
The vapor pressure of water does vary with temperature, although the freezing point isn’t of any particular signifcance.
In the event that there is enough water present to result in 100% relative humidity inside the tire at 70F, then when the tire is cooled to 25F, the condensation of water vapor will lower the pressure by 0.3 psi.
However, if you have filled the tire with air from a compressor with a storage tank, you won’t get much water into the tire. This is because when the compressor operates, it fills its storage tank with hot freshly-compressed air, which then cools back down to room temperature, causing much of the water vapor to condense out (anyone who owns one of these compressors knows that you have to periodically drain the condensate from the bottom of the tank). Then when you dump air from this tank (typically at 125-150 psi) into your tire, the pressure is lowered, and so is the relative humidity. If the tank was at 150 psi and 100% humidity, then when you put that air into a 32-psi tire, the humidity drops to 33%; now there’s 1/3 as much water to condense out when the tire’s temperature drops. If we take this tire from 70 to 25 degrees F, the pressure will only drop by 0.12 psi.
Most service shops will use one of these types of compressors. In fact, they often have dryers in the line to further remove any moisture, as this prolongs the life of pneumatic tools. So the air going into your tires from these places is often very dry.