About 3 months ago, I had my tires serviced at Costco by their tire tech which included nitrogen air refill. My car’s cold tire PSI is 33 PSI per Totyota spec on the label on the door frame. Now being in summer in July, I checked my tire pressure after it sat inside my garage for about 3 hours. I drove it out of the garage onto my driveway in front of the garage, and the tire PSI on all 4 tires were about 35 to 36 PSI. Is this normal? If not, should I deflate a tad? Does cold tire PSI go up a little during summer, and does it go down during winter?
Nothing to worry about here . Also your tire gauge will have a plus or minus factor of a pound or so .
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The recommended tire pressure doesn’t change. Hotter temps than the shop temp when installed will raise the tire pressure. Colder will reduce it. Being 3 psi high is no big problem. You will need to add air in the winter. Air, not necessarily nitrogen. Air is 80% nitrogen anyway so topping off with air is not an issue.
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You can inflate your tires as high as the pressure to which the tire is rated. You get a little better gas mileage with a higher pressure, a little rougher ride, a little less traction, but not unsafe. Many inflate high. Filling with nitrogen is a waste of money.
PV=nRT : 70°F is 521°R (absolute). A 10% difference, say 48° to 100°, makes a 10% difference in pressure. In sunny Albuquerque, where the temperature can go up 60° in a day, the tires on the sunny side in the morning can be significantly hotter than the tires on the shadowy side.
If you want to do that very unsafe practice fine. But suggesting that on a thread for complete strangers is irresponsible. The manufactures put the tire pressure rating on the door plaque for a good reason.
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Wait until first thing in the morning, check your tires then.
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Yes the pressure goes up and down depending on temperature. Air is more dense in cold weather so pressure is reduced. Also why airplanes can get off the ground easier in the winter. But no that’s not enough to worry about in the summer, but if it gets 10 below in the winter, you’ll likely need to add some air.
If it was me, I’d check them in the morning. If they were between 31 and 36, I’d be satisfied. There’s a little error in the measurement and this isn’t a race car that needs really tight tolerances for air pressure. I’ve found that checking monthly is adequate.
Agreed. And being hotter, they have more PSI than the tires on the shady side. I measured this one sunny morning in Montana. I don’t remember the amount of pressure difference, but it seemed significant at the time.
I always have my tire pressures displayed, so I can say that on a sunny day when I get in my car at lunchtime, the tires on the sunny side are usually 1 or 2 PSI higher than the tires on the shady side.
As a compromise between efficiency and comfort.
If you want to personally take a loss in traction to boost efficiency, that’s one thing. Suggesting it for someone else who might need that additional traction in an emergency stop is irresponsible.
The tire tech at Costo might have over-inflated your tires, deliberately or accidentally.
…or perhaps your tire gauge needs to be calibrated or replaced.
In any case, I wouldn’t personally fret over a couple PSI. You can either let some air out or leave it and let them deflate as they normally do over time, giving yourself a week off of weekly tire pressure checks.
Also, inflating the tires with nitrogen is a total ripoff. If they’re doing it for free, it’s okay to let them, but I’d never pay extra for it unless I planned to race my car on a track and each wheel was outfitted with dual Schrader valves (one to suck the air out, and the other to fill the tire with nitrogen).
I thought the maximum pressure was the maximum safest pressure for traction.
You can’t be serious !
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Correct, temp changes the tire pressure. 10% over is not a major concern. The next cloudy day, they might be back to factory. Again, yes, they’ll drop as winter comes on… time to check again.
If your TPMS shows current pressure, you’ll notice being 3 over (cold) has a similar operating (hot) pressure. (At least it does on my tires.)
Really, I just can’t see the fixation on “proper” tire pressure. Being off a few pounds has never been a problem for me. I monitor the TPMS mainly to see if I’m losing pressure like if I hit a nail or something. Otherwise if its in my normal range of 30-34, that’s all I care about-winter or summer. I’ve never run into anyone or skidded off the road by being off a few pounds so relax.
Why do people get so anal about something as simple as tire pressure?
Check the tire pressure in the morning when the tires are cold, and add air if necessary.
Then check the tire pressure again when you refill the gas tank.
Not rocket science.
Tester
The maximum pressure on the sidewall is the maximum pressure recommended by the tire manufacturer. The pressure recommended by the car’s manufacturer, which is usually lower than the sidewall number, provides better traction, and shorter stopping distance.
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No, not exactly. Lowering inflation pressure increases dry traction. (Snow and wet traction are a bit more complex, so I’m only going to discuss dry traction below.)
Ya’ see, tires don’t follow Amonton’s Friction Law (friction is proportional to load). That’s because the tread rubber penetrates the macrotexture of the pavement and gets a boost of mechanical grip. Maximum traction occurs at about 30% slip. That’s why you’ll see little balls of rubber at the edge of race tracks (sometimes called clag). Those are the remnants of the rubber that was torn off.
- AND - the size of the footprint is larger the lower the inflation pressure. but there is a lower limit on inflation pressure below which the tire can’t operate. For example, the lower the inflation pressure, the more heat the tire generates, and heat will damage the rubber.
So there are charts called load tables where the MINIMUM inflation pressure for a given load is delineated. Vehicle manufacturers use those tables to set the inflation pressures for their vehicles. Those tables are published by tire standardizing organizations (the US one is The Tire and Rim Association) and those tables apply to ALL manufacturers of tires. In other words, it doesn’t matter WHO manufactures the tire, the load vs pressure table is the same for a given tire size.
Side note: Yes, there are other tire standardizing organizations in the world and they have ever so slightly different ways of figuring out those tables, so the max loads aren’t exactly the same, but they are reasonably close that they are considered the same within the industry.
And since vehicle manufacturers use those tables, The tire manufacturers also use those tables to design the tire’s footprint to wear as evenly as possible.
Another side note: Vehicle manufacturers are required by US law (since 2008) to affix a sticker to the driver’s door post specifying the pressure for the tire size used. This sticker is commonly called the Vehicle Tire Placard. Prior to 2008, its location was unspecified, but it was required to be on the car since the early 1970’s.
So what about the max pressure listed on the sidewall? There are circumstances where it is better to use a higher pressure than what is listed on the vehicle tire placard. Like when exceeding 100 mph. That’s why the max pressure is imprinted.
And - No! - the max load is NOT tied to the max pressure.
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