PSI, Up/Down???

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May 25, 2005
How much PSI, Up or Down can we run in our tires without hurting their structure? For example, I like a bit more PSI in the front and either, even or less PSI in the rear.

In other words, if my door jamb label says...F:30/R:30 but for ride comfort I like...F:32/R:29, is this OK?

Or, any combination of there or about!

Another example is, I have a vehicle that states on the door jamb label...F:32/R:32 but, I like, F:30/R:28...Is this OK as well?
I can't see such a small change mattering. I suspect the pressure changes more over the coarse of a day of driving than that--start off on a cool morning with the tires at, end the day after cruising hot blacktop.
I am finding that less PSI give us the ride quality that we desire! Even if it's lower PSI than what is required on the door jamb.

I look at the door jamb as ONLY a guideline, not gospel! Maybe if there were always passengers &/or luggage in the rear of the car but, since there is mostly just a tank of gas, I like lower PSI in the real and about the required PSI in the front.

Otherwise, the ride can pound over even small bumps!
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Originally Posted By: Char Baby
I am finding that less PSI give us the ride quality that we desire!

You can go as high as allowed on the sidewall, 45 or even 51 psi for higher speed rated tires, 35 psi for less exotic tires. I've run them that high for autocross and they were fine.
As for going lower than the placard, you could look at your tires maximum load rating and figure out what you are actually using. But you have to know what you are doing as the max load rating is also at the max psi rating for the tire, not door placard pressure, and the door placard pressure can already be borderline low for highspeed hot driving... Think ford explorer.
Probably all the cars in your sig have much more tire load rating than they need and may be able to run lower pressures, but I'd investigate the SUV just to be sure, if its door says 26 psi, I wouldn't go lower...
This time of year when temperatures drop for every 10 degree drop in ambient temperatures tire pressures drop 1 psig.

I always check tires with a digital gauge in the morning before our vehicles are driven and add 2 pounds over the recommended pressures on the door jam. On a trip with freeway driving add 3 to 5 psig over the recommended pressures.

Link to information regarding tires pressures.

See the part about inflation pressures.

Have been doing this for years and in my opinion for what it is worth you get better fuel economy and less tire wear as long as you don't overdo it.
No, the SUV says F:30/R:30

The '06 Mazda3 is the real concern. It states F:32/R:32 and the most comfortable is F:30/R:28. Otherwise the car practically bounces over bumps. The car weights ~2800 lbs and are running "H" speed rated tires...The new Pirelli P7 Cinturato A/S+.

We like the tires but have always run "T" Speed Rated tires on this car. "H" is what's required!
Should be fine...European and Asian owners manuals used to let people vary the psi depending on it's all dumbed down for cafe...35 psi all the time no matter what.
Yeah, 35 PSI is too much for my liking in any of the cars in my Signature. They'd all ride like a buckboard with that much air.

I am less concerned about tire life as, I remove the tires at ~5/32nds of tread and sell them after I've installed a new set of 4.
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Too much air can hammer the strut bearings and damage them in typical street use - remember tires are an integral part of the suspension spring rate.
Since I drive alone and not at the full GVRW I usually run my rear tires a couple psig below the door placard. If the wear on the tire is not wrapping onto the side tread you should be ok. Unless:where you will be loading up 4+ people and a bunch of travel gear - then you have to run the placard amount or a tad bit more.
This is exactly our driving style. Typically, we each drive along in our own vehicles with no extra loads/stuff.

Only once in a while do we at any time, travel with others. And if there are others and their stuff, I/we adjust the PSI accordingly!
I run 47 PSI in an "H" rated tire with a max of 51.

Better miles per gallon, better tire wear.

Lower PSI increases sidewall flex, and makes tire get hotter.
Hotter tire wears faster, and may fail at highway speeds.

Remember the Ford Explorer?
Dealers were told to put a new door sticker on, original had recommended pressure too low, tires failed, vehicle rolled....
You will be fine. I know what you mean about the car bucking, wondering if maybe that points to suspension related issues? Typically an mfr sets psi at a rate to optimize fuel and comfort. At those pressures im sure you will be fine though..but i would make sure it wont go less than thats when you might be more succeptible to a flat.
I still can't believe ford specified 26 psi for the Explorer. That was way too low for a SUV. My truck calls for 36 psi. Tire wear is fine and it rides OK. If I know I am going to haul with it, I raise the pressure to 40 or 42. They have a 44 psi max. At 40 psi it has a firmer ride which I prefer, but I get increased center wear on the tires. I get an increase in mileage too, but not enough to cover the cost of the increased wear on the tires. Most tires at max psi are rated for more weight than a vehicle can carry, but not always.
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I always chalk test my tires.

Run a line of chalk across the tread, drive 100 feet or so, and see if the chalk line wears away evenly.

Higher PSI in tires to get more MPG is false economy, unless your tires costs less than ~$40 a tire or you drive less than 2,000 miles a year.
Where are you going to find a tire pressure gauge guaranteed accurate to 1 psi?

I bought a Milton S505 tire inflator. Figured I'd buy a good one. The calibration was different from my other gauges which were consistent with each other, including an industrial pressure gauge I fitted with an air chuck. I contacted Milton about calibrating the S505. Their answer was that it was not able to be field calibrated, and any reading within 3 psi met factory standards.

So...don't worry about a psi or two. You could buy something like an Ashcroft 1084 0-60 psi 3" test gauge, accurate to 0.5% of the full scale reading anywhere on the scale (3/10ths psi anywhere on the scale), about $200. Don't use it after you drop it even once. Other pressure ranges are available at the same 0.5% accuracy. Or an industrial gauge at accuracies up to 3%, about $20, but again, 3% of the 100 psi scale range is 3 psi anywhere on the scale. If it's a 60 psi scale, 3% of that will be about 2 psi accuracy anywhere on the scale. For the consumer grade digital gauges we buy--who knows?
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