I’m interested in safety and wear on the tires

Stick with what OEM recommends, in your case it sounds like 30psi. And if you ask me, 31 is close enough if you like that number!

 

Thanks! That’s what I was thinking too. I’m loving this forum.

 

I've always run mine 3-4 above what the sticker says (because it usually looks flat otherwise) without any wear issues. Supposedly gets more mpg but nothing too noticeable.

 

It is better to be a bit above the pressure stated on the door sticker than it is to be any amount below that pressure. You won't have undue wear from a pressure 5-10 psi above that stated on the sticker, but you will have a stiffer ride (harder tire), some amount of added protection to your rims (more resistance to bottoming out the tire in a hole or bump), better fuel economy, somewhat less dry/wet traction (smaller contact patch), somewhat better snow traction (harder tire and smaller contact patch is more likely to get to the road surface instead of floating on top of the snow).

Pressures below that stated on the door sticker make you susceptible to overheating the tire; the faster you're driving and the more underinflated you are the more risk. And it takes only a few psi below the door sticker pressure to have a meaningful detrimental effect. Your ride will be softer before you die though.

 

It is better to be a bit above the pressure stated on the door sticker than it is to be any amount below that pressure. You won't have undue wear from a pressure 5-10 psi above that stated on the sticker, but you will have a stiffer ride (harder tire), some amount of added protection to your rims (more resistance to bottoming out the tire in a hole or bump), better fuel economy, somewhat less dry/wet traction (smaller contact patch), somewhat better snow traction (harder tire and smaller contact patch is more likely to get to the road surface instead of floating on top of the snow).

Better wet traction.

Hydroplaning speed is directly proportional to tire pressure.
At 28psi, you'll begin to hydroplane below 60mph.

 

I thought it was the other way around. Now I gotta go do research. Lol.

Navy research at Pax river showed that. I've looked an haven't been able to find links to that, but here's a document from Purdue in MPH rather than Kt

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2919&context=roadschool

(link opens a pdf, also attached below)

Converted from kts to mph:
Vp = 10.2 * (sqrt P)

28psi = 54mph
35psi = 60mph

 

Converted from kts to mph:
Vp = 10.2 * (sqrt P)

28psi = 54mph
35psi = 60mph

Is this a fancy way of saying that the weight your carrying doesn’t really factor in to the equation? That’s hard to believe. Maybe I misunderstand.

this is the excerpt:
“This can be more easily understood by realizing that the tire is flexible, and deforms under changing loads. It turns out that the ratio of weight carried by the tire to the area of tire contact on the pavement remains about the same, and this ratio of weight to area will always be very near the tire inflation pressure.”

 

My impression is that the door sticker pressure is the mfr's balance between being low enough for the most ride comfort, but not so low that you would overheat the tires (except in the case of the 1990s Ford Exploders). So it isn't necessarily optimized for those other circumstances. I choose to ride at 40 psi for better rolling resistance and am cognizant that my dry traction has suffered a little bit.

 

imho

The door jamb number represent the floor of what any tire regardless of brand should be at when cold.

The Max PSI stamped on the tire sidewall represents the ceiling of what the tire can accept at cold temps.

Any number in that range is fine, but they come with caveats, such as if you go towards the high end of the spectrum you risk wearing out the center of the tire quicker.

Anywhere near those numbers should be fine for a tire that will be used in driving (toyota recommends airing beyond max PSI during transport to prevent flat spots so whole another can of worms).

 

Actually, the manufacture door jamb PSI (COLD) is a compromise between: MPG, tire life, and passenger comfort. IMO, I think the auto manufactures value comfort and MPG in their PSI recommendation; slightly underinflated for ride comfort.

The lower the PSI: the greater the rolling resistance, the worse the MPG, softer rider, outer edges wear faster
Manufacture PSI reccomendation: sweet spot of MPG, MOST comfortable ride, OK tire life
The higher the PSI: less rolling resistance, better MPG, firmer/harder ride, center of tire may wear faster

NEVER exceed the cold PSI rating of each tire. If you had cheap tires w/ a max PSI of 28, you would be 2PSI over following the manufactures tire inflation recommendation.

30 PSI (manufacture recommendation) vs 31 PSI; IMO, the difference will be negligible. After many tanks of gas, the difference might be noticable.

I vote go to 33PSI for a week or longer. You might notice the ride is a little firmer or not. MPG might be slightly higher. Tire wear might not be any different.

If you were to have the car fully loaded (people and/or stuff in trunk and rear seat), increasing the PSI would be good, esp if on a long trip. You would just need to adjust the PSI back down when COLD, and not longer carrying all the extra weight.

Don't forget to check your spare tire at least 4x's a year. Remember, temperature and PSI are proportional. A tire properly inflated for summer temps, will be under inflated in winter temps, in addition to loosing a few PSI per month.

 

And FWIW, I've always run my inflation high, and I do monitor my tread depth across the face for uneven wear.

The most common argument against elevated inflation is "You'll wear out the middle of your tire"
Maybe inflated to 55+ like many "hypermilers" do, but I've not encountered that in probably a million miles (seriously). I still wear the edges slightly more than the middle, or they wear evenly.

My crime against tires is not regularly rotating them.

 

The most common argument against elevated inflation is "You'll wear out the middle of your tire"

I have found this to be a myth too.

 

OP should experiment tire PSI. Lets say current tires show MAX PSI is 45PSI

Trial 1) inflate to 45PSI, drive around for a few days. You will MOST likely feel it, and NOT like it. The ride will be hard, but MPG will be best due to decreased rolling resistance.

Trial 2) inflate to 40PSI, drive around for a few days. Make a note of what you feel, hear, like/don't like.

Trial 3) inflate to 35PSI, drive around for a few days. Make a note of what you feel, hear, like/don't like.

Trial 4) inflate to door jamb PSI, you already know what it is like and the MPG you have been getting.

I think OP will like 35PSI, b/c slightly better MPG (possibly 1-2MPG better), and no significant ride/noise difference, and likely no adverse tire wear difference (possibly better tire wear).

36PSI-40PSI will give better MPG, but might feel a harder rider and possibly hear noise.

 

I’m going to experiment a little for sure.

 

Dang folks we running RCTs for tire pressure?

Side note, do tire mfgs stamp minimum PSIs on tires? I understand the door jamb is the "best" psi based on their internal targets and testing but what about the tire mfgs opinion?

 

Dang folks we running RCTs for tire pressure?

Side note, do tire mfgs stamp minimum PSIs on tires? I understand the door jamb is the "best" psi based on their internal targets and testing but what about the tire mfgs opinion?

They generally stamp only max. As HP indicated, they may indicate an upper range, that may be an Aus thing, as I've not seen that here.
On some tires (used to be all) it was "Max Load at XXpsi"
Indicating that the load capacity of the tire was dependent upon the pressure... and it still is, but it would be extremely uncommon to find a passenger car tire of insufficient load rating for modern lightweight vehicles.
Light truck tires OTOH, will generally indicate such, and heavy tires such as load range D and E can have sidewall max inflation as high as 85psi. The tires on the C5500 trucks at work require 105psi.

The whole Firestone/Ford Explorer issue was because Ford was recommending inflation of 28psi (for comfort) on LT/SUV tires that should have been run at 35psi or higher.
Tires overheated at highway speeds due to sidewall flex, and they shed their tread.

And yes, trusting the door jamb will give you an acceptable compromise between comfort, handling, MPG, and tire life... favoring comfort.
But in reality, you can often get the same size and brand/model tire with max PSI perhaps 5-10psi different, perhaps due to the speed rating or load range.
Anything at or above the door jamb pressure is going to be safe. I would never go below, and flat out ignored the old stickers in the 70s and 80s that listed 32 for the front and 28 for the rear.