Uneven tire pressures questions


#1

I was curious to wonder what can happen to a car with uneven tire pressures across it’s 4 tires. e.g. left side vs right side, front vs rear, where one side/set is 1-2 psi off from the other.

Is it going to cause any problems long term if left that way or negligible? If problems, what kinds? And ok to leave it that way for a few days to a week or two? Or should really readjust pressure ASAP? Also, if you were to normalize the pressure across the tires and assuming you buffer extra in the tires (e.g. up to 5 psi extra), then what do you usually do - bleed down the higher pressure tires or pump the lower pressure tires up to match the higher one?


#2

Set all the tires to the pressures recommended in your owner’s manual. Those numbers are also on a label on your driver’s door jamb.


#3

To answer the OP’s question, the tire pressure listed on the door jamb and in the owner’s manual is typically determined to maximize the tire’s contact patch with the road. This allows for best overall traction and tire wear. So, uneven tire pressure would then lead to uneven traction and tire wear issues. Also can lead to vehicle instability problems, since the tires are designed to flex, but uneven tire pressures causes the tires to flex differently. Tires on the same axle, like both fronts, have the same recommended tire pressure and it is not unusual to see different recommended pressures from front to rear. I think most passenger cars can easily tolerate a difference in tire pressures of 2 psi above and below recommended. At 4 psi below recommended, fuel mileage can suffer. Underinflated tires tend to wear out the edges of the tire tread as the tire tends to cup. Overinflated tires wear down the center of the tread.


#4

One or two pounds difference is not enough to lose any sleep over…Anything over three pounds should be corrected…Today, all car owners should carry a small 12volt compressor designed for inflating tires…Avoid the cheapest ones, choose something in the $20-$30 price range…Harbor Freight has a nice selection…Pick up a decent tire gauge while you are at it…The $1 pencil gauges are better than nothing but not by much…


#5

And check pressures in the morning, before you drive anywhere. Driving heats the tires, increasing the pressures. The pressure on the sticker is for a ‘cold’ tire.


#6

You can see 2 psi difference across cold tires side to side based on the sun shining on one side. 2 psi is not worth worrying about. Your gauge is not likely better than +/- 0.5 psi anyway. That means the measurement could be off by 1 psi just from the gauge. As long as the TPMS doesn’t flag the difference, it is unlikely you’ll feel the difference.

BTW, There are people who CAN feel the difference. They work for the automakers developing cars and get very familiar with each model assigned to them.


#7

texases wrote:
And check pressures in the morning, before you drive anywhere.

If the car is in a garage in the morning, then don’t forget to add 1 PSI for each 10 degrees that the garage is warmer than the outside air.


#8

@cdaquila–You might want to be aware that posts are disappearing from this forum…again.

I posted a comment at around 7:30 this morning, and although it did appear in this thread at that time, it is now among the missing.


#9

@VDCdriver‌, oh, no! If it’s happening to anyone else, let me know. Thanks for keeping an eye on it.


#10

put the recommended pressure in all tires when there cold. driving and sitting in the sun or in a hot garage may raise the pressure a little so try and get the reading cold. exceptions can be made from front to back in 2wd cars for performance applications. but for awd and normal circumstances same tire and recommended pressure on each tire. this assures more even tire wear and handling. over inflation and under inflation can cause problems with handling and tire wear and may be unsafe to drive on. uneven tire pressure can do the same along with putting a strain on the drive train if the tires are to uneven.


#11
"...the tire pressure listed on the door jamb and in the owner's manual is typically determined to maximize the tire's contact patch with the road."

Since the door jamb pressure is the same for all 4 tires, and a typical FWD car has 60% of its weight on the front tires, this can’t be true. Also, the maximum tire patch occurs when the tire is flat. I set my rear tires at “door jamb” and front tires at “door jamb” + 3psi (FWD car).


#12

The disappearing post has happened to me twice in the last week.


#13

@oldtimer11, do you recall which threads contained the disappearing posts?


#14

I get very long life from my tires, and I am pretty aggressive in cornering, not many others can keep up with me on a curvy back road. I use the tire placard as a guide, but I do go a little overboard. First I have a non contact IR thermometer and I check each tire for temperature. I prefer to check them early in the morning before the sun shines on any of them, but my driveway is shaded for most of the morning.

Some vehicles have different recommended pressures between the front and the rear. Mostly that is with trucks, but my Subaru recommends 33/32 front/rear. I add 3 psi to this. My reason for this is that tires lose air over time, about 1 psi per month and I only check them quarterly. I over pressurize the tires and then bleed down to what I want. I use a digital gauge that reads in 0.1 psi increments and had a calibration certificate traceable to NIST standards.

It is also important to be vigilant for odd tire wear patterns. As long as the tires are wearing evenly and at a normal rate, I do not mess with the alignment. As soon as an unusual pattern shows up, I check the alignment. But if the tires are not showing any unusual wear, I leave the alignment alone. I won’t even allow a tire store to give me a free alignment check.


#15

@keith, are you kind of suggesting an alignment check can be bad if nothing appears to be wrong with the tire wear or steering of car? Or you are just being overprotective in that sense?


#16

“Remember to add 1PSI for every 10F the garage is warmer…” “And check pressures in the morning, before you drive anywhere…”

Really, we’re talking about measuring tire pressures with a cheap-o pen gauge, and maybe bothering to correct things if you’re more than +/- 4 PSI off or so. While I might grant ideal gas laws and whatnot, I don’t think a thermometer reading of your garage is necessary to tell if your tires are flat, nor do I think that a sedate jaunt to the local gas station will make using the air there moot.

I mean, when you diet, do you account for the position of the moon to correct the scale reading? Theoretically, you should; you can probably even measure the difference between moon overhead vs. lunar midnight on a good scale.


#17

I have a Black and Decker Air Station pump. The dial gauge is accurate and there is a rotating ring around it that sets the auto stop on the pump. You can do something else instead of tending the pump. The pump runs on 12vdc and 120vac. It cost about $50, and is worth it for the features and accuracy. I still use my dial pressure gauge, but all that seems to do is confirm the accuracy of the pump gauge.


#18

meanjoe75fan wrote:
Really, we’re talking about measuring tire pressures with a cheap-o pen gauge, and maybe bothering to correct things if you’re more than +/- 4 PSI off or so. While I might grant ideal gas laws and whatnot, I don’t think a thermometer reading of your garage is necessary to tell if your tires are flat, nor do I think that a sedate jaunt to the local gas station will make using the air there moot.

My garage can easily be 20 to 30 degrees warmer than the outside air, which translates to 2 to 3 PSI. If you want to consider that as inconsequential, you’re welcome to your position, but I don’t agree. When you consider how many people don’t check their tire pressures often enough, starting with tires that are 2 to 3 PSI low and then letting them drop from there (especially this time of year with outside temperatures dropping) seems like a bad idea to me.