Tire air pressure

tiredrunner

I'll preface this topic by saying that I'm aware of the different schools of thought when it comes to air pressure and vehicular tires. While I have and exercise my preference, I also seek your opinions.

I drive a 2007 Honda Accord sedan with I4 engine. I've owned the car for the past eight years. One of the first things I replaced was her shoes and I went with Kumho TA-11 all around 205/60 16's. The max air pressure stated on this tire's firewall is 44 PSI, so I always fill them to 40 PSI.

Why 40 PSI? My school of thought is; When the weather gets cold or it warms up, the air inside the tires contracts or expands up to 3 PSI. If it warms up, the pressure could expand up to 43 PSI, and when it cools, that number can drop to 37 PSI. In both cases, the air pressure is within the defined spec of the tire.

The Honda manual states tire air pressure should be 32 PSI. I personally find this spec to be asinine and designed to absolve them from liability, which is understandable. I've driven the car with the tires filled to 32 PSI. The car lags very bad and handles like shit. At 40 PSI, it feels just perfect. I simply tap the gas pedal and the car moves normal.

One other concern I have about operating the car with tires at 32 PSI is the firewall sag. I'm middle-aged and have the typical body sags that come with that, but that pales in comparison to what the tires look like at this air pressure. At 40 PSI, the sag is minimal.

So there you have it. What do you follow? The tire manufacturer's spec, or the vehicle's spec? Or what is your preference?

TIA

urbanriot

tiredrunner What do your tires say?

Here in the North we swap tires in the winter and the listed max PSI for my winter tires is different from the listed max PSI for the summer tires and both are different from the door jam PSI.

The listed tire pressure on a tire is typically the maximum pressure and not the optimal pressure, whereas the door jam pressure is the optimal pressure.

32 ~ 34 PSI is a good average for almost every vehicle and tire in existence on a consumer vehicle.

Thane_Bitter

tiredrunner Radial tires tend to look saggy, its how they are built. Under inflation is terrible for them and will cause the sidewall to heat up so much that the material disintegrates via the heat generated (thermolysis) untill its mechanical properties null out and the entire things rips apart, with the sidewall remains being shreaded and fussy, little rubber crumbs may also be present in what remains of the rest of the tire carcus.

Yes the placard markings are for general use, depending on the tire, conditions you may need more are. I am tempted to call them bare minimums but there could be exceptions when going below their recommended pressure is needed or desired in rare cases or extreme conditions.

On that note my all weather tires (not the same a all season) need more air much as you have discovered, I found that using the stated pressures on car’s placard was too low and causing the edges of the cap to wear out faster than the center. The rest of the tire wear was typical and the suspension system was fine as was the alignment, it was just that they needed more for balanced wear. Increasing the pressure (but ALWAYS below maximum stated pressure on the tires sidewall) I was able to correct the wear and then go to a pressure that was higher than what the manufacture of the vehicle stated but below what I had been using to balance out the wear. On a different vehicle the manufacture’s settings are fine and tire wear is nominal with use despite having entirely different tires for half the year (Winter and all season tires).

So there you go, do what works best for you, don’t go above the cold max temperature printed on the tire sidewall and keep monitoring your tire pressure and tires for wear and damage.

Somewhat-Reticent

Depends on the load. ( And weather, as noted. And road conditions. … )

px_eliezer_

IMHO, "Maximum" means Maximum, which could be quite different from Recommended or Optimal.

Do you still have access to the Owner's Manual which may have additional comments.

The tire manufacturer says:

Air pressure for your new Kumho tire should be set in accordance with the vehicle manufacturer`s specification IF IT IS THE SAME as the size originally equipped on your vehicle.

(Text adapted for a glitch in the forum software).
https://www.kumhotireusa.com/us/cont/content.do?menuCd=MN000182

JRB-Ware

Manufacturer recommended tire pressures are based on safety and fuel economy. Set and don't fret.

Andyross

The correct recommended pressure is also on a label, typically on one of the door jambs.

Overinflating a tire can lead to poor traction and uneven wear because you are riding only on the center instead of the full width. It can also reduce traction in the snow. It's only helpful if you drive in sand. It can also cause an unnecessarily harsh ride.

I personally try to keep it, when not driven for awhile and out of the sun, to no more than 2-3psi over recommended. If I know temps will be going up over the next few weeks, I may keep it near recommended. My car has 4-tire pressure monitoring, and just driving a few miles can increase it 3-4 psi. That is taken into account with the recommendations.

It's also somewhat normal for the recommendation pressure to be a bit lower in the back than the front, especially on a front wheel drive car. Not only due to weight difference, but for most basic drivers, that may let the front end break loose first (understeer), which is easier to control than having the back end break loose (oversteer.)

real_aurgathor

The tire pressure should ensure proper contact area and equal loading over the contact patch, and there are a few different procedures (some with chalk) to determine what is the correct pressure for a given load.

Much higher than optimal pressure can significantly reduce traction on wet roads in particular because of the significantly reduced contact area, and at 40 PSI vs 32 you are most likely well over optimal tire pressure.

Unless you actually verify that you still have a good sized contact area at 40 PSI, you probably don't want to pump up your tires that much. I usually inflate my front tires to about 10% over recommended pressure, but leave the rear tires at the recommended pressure unless I carry something heavy in the trunk, or in the bed.

Andyross Overinflating a tire can lead to poor traction and uneven wear because you are riding only on the center instead of the full width. It can also reduce traction in the snow. It's only helpful if you drive in sand.

Actually, you want to underinflate in sand, not overinflate.

egeezer

How evenly are your tires wearing?
Are they wearing evenly across the tread, or more inthecenter or on the edges? A tread gauge may be a good investment if you're interested in maximizing tire life.
Wear in the middle = overinflation
Wear on both outsides = underinflation.
Uneven wear on one side = possible misalignment.
Also, how often do you rotate the tires?
I bought my tires at a shop that provides free rotation and balancing(if needed) every 7000 miles.

tiredrunner

egeezer Tires look like they're wearing evenly. I rotate them every 5k miles.

Honda says 32 PSI is recommended for this car. At that pressure, not only does the car feel like it lags but fuel economy definitely dips.

Andyross

real_aurgathor
Sorry, did get the sand backwards. Some people think you can do that in snow, but that just causes it to compact and lift you off the pavement.

Rich221976

I tend to add about 1 to 2 PSI when I am adding air to my tires. My vehicle requires 31 PSI for all 4 tires. So I drive to the nearest free air at the gas station and put in 33 PSI.

That will normally get me to 31 if not only 1 PSI over. Since I have to account for the driving to the gas station.

However, I am due to put air in my tires since according to my vehicle sensors I am at 29 PSI

Somewhat-Reticent

A local tire shop gave me an estimate that included pressure sensors.
My vintage rig doesn't have that feature.

real_aurgathor

Of course a 25% overfill will give you a firmer ride and a noticeable boost in mpg -- they are given at that level.

TC1USCG

On my cars, I air to the middle of the door jam and whats on the tire when cold. On the Jeep, depends on my mood. I normally air the same way but rocky area, airing down to 10lbs or so is taking a chance of breaking the bead or pinching the sidewall.

real_aurgathor

TC1USCG

There are a few cases when one should significantly deviate from the recommended pressure -- one such example would be driving on sand, another is when carrying an unusually heavy load.

One time I was helping a then GF to move and she had a pile of bricks that was about 1.5 ft high in the rear of my station wagon -- it was heavy enough that completely compressed the rear springs and the car was riding on the axle. That was one of the funkiest handling I've ever experienced. Luckily, that was a relatively short drive on mostly rural roads with very little traffic.

Another time with a bit more weight with paving stones, but that time in the back on my Bronco, which is essentially a 1/2 ton truck. I noticed the funny handling -- checked my tires and the rear ones were hot even though it was after sunset and cool outside. So I ended up going from 40 or so to 55 into my C rated tires, and that fixed the handling and led to much cooler rear tires. (that was a 300 miles long drive, not just a few local miles)

RayGeode

I just took delivery on a brand new Forester. The air pressure was near 40 all the way around. To ignore the recommended 33/32 pressures, I can guess they meant to improve the gas mileage which stands at 23 after about 475 miles, half local and half highway driving. Ouch! They advertised it at 28 mpg combined.

takeahike

RayGeode

Are you going by what the mileage calculator–mine is on the center dash–is saying or the old-fashioned way by dividing the miles driven by gallons it takes on a fill up? The calculator is certainly a challenge on mine, a 2023 Forester Premium. Around town it doesn’t report well but then again my GF who usually drives is kind of a lead foot–typically around 20-22. But on the freeway it does a lot better, usually getting up to about 33 or more after a while. I am a more conservative driver, and I’ve had it up to as high as 43 after a while on the freeway (just once). I don’t think that you can rely on the calculator too much as a reflection of what’s really happening because of the way it just moves very gradually from the last reading and therefore takes a while to adjust to what is actually happening at any given moment. Of course the best and most accurate measure is that old-fashioned way of setting the trip odometer back to zero at fill up and then dividing the miles recorded by the amount of gallons it takes on the next fill up. Unless that’s what you are already reporting on, if you have time let us know what that method shows.

Have you heard that the best mileage is obtained by driving like there’s an egg under the pedal? Slow starts are of course the key because of course accelerating from a standing start is when the MPG is poorest.

tiredrunner

RayGeode In the fours years I’ve lived here so far, one thing is certain; Norwalkers love their Subarus.

🙂

I’m personally not sold on Australian engineering. Blown head gaskets should be an American thing only.

real_aurgathor

RayGeode

MPG in local driving can vary a lot depending on traffic, so it may not be a good measure of the car’s capabilities. I have a ’95 Ford Bronco, and I didn’t even bother much to calculate in-city MPG because that was in the don’t even want to know category. 😒

On the other hand, with careful driving, I could normally get 1 - 3 MPG better than speced on highways.

RayGeode

takeahike I am a more conservative driver, and I’ve had it up to as high as 43 after a while on the freeway (just once).

I’m also that kind of conservative driver so I can’t wait to start one of my road trips I’ve been planning on and catch some 30+ mpg driving.
I’m just using the reported mileage on the instrument display until I learn my way around the ins and outs of settings.
Thanks for the words of advice.

egeezer

takeahike

I always check miles driven versus gsallon at fillup. Since the shutoff on gas station nozzles may be different, I average two or three fillups under similar weather and driving conditions.
My Sienna under usual driving averages 21 MPG cold weather, 25 warm weather.

Windy weather can hit mileage pretty good too. I noticed the real time mileage on the Sienna can drop 5-7 MPG, and increasing 4-6 mpg with the wind(accuracy may not be great, as this is an informal observation).

Oh, BTW I inflate tires to 38 PSI on the Sienns, 35 PSI on the Avalon. I use BlueDriver when I do real time observations on the Avalon.

RayGeode

tiredrunner In the fours years I’ve lived here so far, one thing is certain; Norwalkers love their Subarus.

🙂

I’m personally not sold on Australian engineering. Blown head gaskets should be an American thing only.

Are you a Norwalker too? If so welcome, and hope you enjoy it here. I’m lifelong , 71 years truth be told. Garavel expanded quickly and took over a huge piece of choice real estate and looks like business is good for them. I bought from them because of their presence and also the Consumer Reports rating. It’s my first Subaru after Datsun, (yes), Mazda, Toyota, and VW.

So what’s Australian about? And I wouldn’t want a blown head gasket either. I baby my cars

RayGeode

real_aurgathor I have a ’95 Ford Bronco,

Wow, classic, take that down to the classic car rallys

tiredrunner

urbanriot My tires say 44 PSI max. I use them all year round.

The label in my door jamb says 32 PSI.

Eff that.