Plan B Forum

When I got sharky corollaline her tires were inflated by the dealership and they consistently for many months read around 42-37 with the back tires slightly lower.

Overnight in the cold they would drop but then in the warm go back up - I do understand that the temperature affects psi.

The tire pressure is one of the statuses that shows up on my phone app so I’ve monitored it daily and not had any issues until recently.

When the temps dropped to where it’s colder during the day like 50s, suddenly the psi is showing up between 33-31. I had a corresponding drop in fuel efficiency from ~40-42mpg to ~35mpg.

So I used my cousin’s cool air compressor to fill them back up today, I set it for 40 in the front and 38 in the back. I got 41mpg on my work commute directly afterward.

So the door sticker does say that 35 front and 33 back is the recommended. On Reddit people said going higher is okay and will get better fuel efficiency but stiffer ride. I don’t mind the stiffer ride because I drove an SUV for 20 years and it was also how I thought this car was supposed to feel until the pressure dropped recently. I didn’t really like the lower psi ride, it seemed sluggish.

So what I want to know is, will setting this higher psi result in a substantially shorter longevity of the tires themselves? What if any negative impact will there be from choosing to inflate more?

I’m assuming it’s not unsafe because the dealership - or factory - set it high to begin with.

Thanks in advance for the motorhead/engineering expertise I know I will receive.

The rougher ride is a result of the tire not being flat on the road surface. Higher pressure pushes the centre further down which may give more mileage, I suppose from less contact friction area. But the tradeoff is uneven tire wear and less safety. (Less tire surface area on the road means less grip). The manufacturers recommend tire pressures for good reason - under and over inflation are not happy things

It handled well in the snow and ice last year - I bought it a year ago this month so it’s been through a winter of being set that high by the dealer/factory when I took delivery and we had a few substantial snow events last winter and the country roads I commute on are typically not very well maintained.

The logic of what you say computes, I’m just wondering why the tires were inflated up by the dealer/factory if it’s not safe?

I don't know if it's a fact, but I once read that tires are overinflated on new cars at the factory so they won't develop flat spots from sitting for long periods of time.

Other than that, Meade's advice sounds good to me.

At a guess, the risk factor is not very high at first (unless ya hit a pothole hard as I did in my Corolla in the first month and popped the tire). The problem with continuing to run hard is the wear over time. If the center is wearing more than it should, then at some point the portion of tire you're actually connecting to the road loses grip. Especially with all those F1 speeds around corners . . . OTOH

You should keep the tiers near the recommended pressure (within a few PSI) and remember the amount you overinflated the tires in the winter will increase in the summer

Okay, your comments all make sense.

But I just have to say, what use is a status sent to my phone daily if it says ‘good’ for overinflated same as it says ‘good’ for properly inflated?

BoSoxGal wrote: ↑

Wed Nov 05, 2025 11:31 pm

Okay, your comments all make sense.

But I just have to say, what use is a status sent to my phone daily if it says ‘good’ for overinflated same as it says ‘good’ for properly inflated?

Maybe daily status is useful in that it would let you know if your tire pressure was too low.

Joe Guy wrote: ↑

Thu Nov 06, 2025 12:22 am

BoSoxGal wrote: ↑

Wed Nov 05, 2025 11:31 pm

Okay, your comments all make sense.

But I just have to say, what use is a status sent to my phone daily if it says ‘good’ for overinflated same as it says ‘good’ for properly inflated?

Maybe daily status is useful in that it would let you know if your tire pressure was too low.

I guess not, because when they dropped in recent weeks they fell to 30, 31 and didn’t trigger any kind of notification to fill them. It kept saying tire pressure ‘good’ despite being under the recommended psi.

I wonder how low they would have to go to trigger as ‘not good’?

BoSoxGal wrote: ↑

Thu Nov 06, 2025 12:47 am

I guess not, because when they dropped in recent weeks they fell to 30, 31 and didn’t trigger any kind of notification to fill them. It kept saying tire pressure ‘good’ despite being under the recommended psi.

I wonder how low they would have to go to trigger as ‘not good’?

The TPMS on my car is supposed to alert me if psi goes 25% below the recommended level. Your app is probably similar to that.

So what’s the easiest way to let air out of the tires, but not too much?

It's easy if you have a tire gauge. Just press the pin in the valve stem a little bit at a time and keep checking the psi. It doesn't take much time for the pressure to lower, so quick blasts are the best way. And as you probably know, it's best to adjust tire pressure only after the car has been sitting for a while.

One other thing follow the recommended inflation on the tires not necessarily the automakers recommendation (they should be the same if not very close 2~3 PSI either way)

One thing of note is over inflating tires (to a degree) is less dangerous than under inflating. Increased heat and friction speed up tire wear and breakdown. Over inflating decreases friction due to reducing the tire contact with the pavement while that can improve mileage it also degrades handling and more importantly breaking as friction is exactly what makes it work. Incidentally as increased friction equals better traction in a pinch letting some air out of your (drive) tires may help if you get stuck in a poor traction situation. (Carrying a portable compressor would be recommended before trying this)

I agree; one other thing, I do think setting a threshold of 25% to trigger a notification on your phone makes a lot of sense; any less (given how tire pressures fluctuate due to ambient temperature and driving), and many people will either ignore or disable the app. Likewise, as CP notes, people do differ as to the inflation pressure; I also try to use the pressures recommended by the tire manufacturers rather than that of the automakers and a constant alarm/notofication because of this woudl likely lead to the app being disabled.

FWIW, I do think the pressure monitors are useful because it is difficult to see whether a tire is going flat by visual inspection due to the modern low profile tires usually used.

Also, my dealer says it inflates all tires with nitrogen which does give some benefits (mainly no oxidation of the rubber from ambient air under pressure, but I really don't know if it is a benefit--it is used in auto racing to reduce the risk of fire to heat buildup, but this is not as much of a danger during ordinary driving, so I really can't assess the benefit of it.

Two things. Tire pressure gauges are notoriously inaccurate - the only ones I trust for an accurate reading are at tire dealers. They pay a lot for their gauges and they can (or should) calibrate them regularly against a verified source. My local gas station has a pump which costs $2.00 and the first (and last) time I used it, the gauge was off by 10 psi or so. I went in and told them. They told me that it wasn't their problem, the compressor is owned and operated by a separate company. I wanted to say (but didn't) "Fuck you!" My tire place will check them for free.

Secondly, driving does not make a huge difference. Certainly the tires heat up; but maybe by 25°C from ambient in normal driving. Given that absolute zero - the use temperature for the Gas Laws - is negative 273°C, you might get an 8% shift in normal driving. That's why they tell you to check pressure when the car and tires are cold.

Modern cars and modern tires are much more forgiving than they used to be.

OK three things. There is absolutely no benefit to using nitrogen in your tires. (Except to the dealers who is laughing all the way to the bank.)

I think there might be some slight benefit, but it's not worth it if you are charged for the nitrogen *unless you are also paying for air). But my dealer provides this for free. (and, FWIW, I think the nitrogen concentrators they use are fairly expensive and it would take a lot of nitrogen fills to overcome that up front investment; I think my dealer does it to provide the illusion of premium service to customers. Personally, I wouldn't pay more for it, but if I am getting the service done by them, it's fine)

As for tire pressure, I have one of those pen gauges where the pressure is read on how high it drives a piston inside the sleeve up and I have found it pretty good, generally as good as the tire sensors, and a lot better than service station air pumps. Indeed, if you think you may have to add air sometime, I would recommend buying even a cheap gauge as it will be better than the setting on the pump.

FWIW - Speaking of tire gauges, coincidentally, yesterday I received a notice from my Consumer Reports online subscription about tire gauge ratings. I don't think a link would work for non-subscribers but here are the top 5 - but lower on the list, the Victor 00876-8 for $5.90 at Amazon, is rated at 5/5 (highest rating) for accuracy - the same as the top 3 listed here (4 & 5 are rated at 4/5)

The one I have and have had for years is like the one in the middle - but it wasn’t $55.

BoSoxGal wrote: ↑

Thu Nov 06, 2025 7:31 pm

The one I have and have had for years is like the one in the middle - but it wasn’t $55.

And now that one is listed at Amazon for $77.99 and they say that's a 22% discount!