quote:

Originally posted by Aeteocles:
Pressures indicated on the door plate is for normal daytime temperature, and unladen.

You will have to compensate for temperature if the air is cold (like wintertime) or if the air is hot, or if the tire is warm from rolling.

Heavier loads require more pressure to maintain the proper amount of deflection as the tire rolls. If the tire is under inflated for the load, the tire will deflect too much at each revolution which creates excess heat. The excess heat can cause the tire to delaminate and blow out while driving.

Makes sense, thanks! I've always added 3 or 4 extra pounds if I'm carrying a load more than a short distance.

When in doubt, and if using the stock tire size as is listed then go by the plate on the door. If you've changed tire size or gone from a p metric to a lt then there's a calculator online that will get you close then chalk test it.

Example: my 4runner came with 265/70/17r size tires. Standard psi would be 32. It currently has lt275/70/17r on it so current psi is 39 cold after using the calculation to get close and then chalking it to figure out the tread wear.

I always do what's on the door plus 2-3 psi and fine tune from there to where I like the ride comfort. My cars normally come with runflats and I replace them with goflats and if I went by what's on the door, the ride is too soft.

At my last alignment they started to lower the pressure and saw that I no longer had runflats so they put it back to where I was before they threw weights in the car to start the alignment. I actually told them to just put 200 lbs in the driver's seat and do it from there since I'm alone 90% of the time.

 
The chalk test for the win. Every vehicle I have ever chalked results in a pressure 2-3 pounds higher than the door plate. I suspect the door plate reflects the manufacturer's desire to provide a "smoother" ride, thus enhancing the experience of their vehicle. Chalk it if you want maximum wear from your tires.

Air carries the load. The more air the more load a tire can carry up to the max pressure on the sidewall. There’s three ways to get more air: bigger tires, more pressure, or more tires.

More tires like with a dually pickup vs a single rear wheel pickup.

More pressure, like light truck tires (LT). You can find load inflation chart for your size tire that will tell you what it’s rated to carry at various pressures. As pressure goes up, so does the weight it can carry. An example would be the door jamb sticker for an F250 with 275/70r18s calls for 65psi front and rear while the same size tire on the F350 SRW calls for 65psi front and 80psi rear.

That leads into the question, do you put more air in the tires of a pickup when you carry a load? I do for the rears up to the max pressure, 80psi, on my tire’s sidewall. Empty, there’s only 3,300 pounds on my rear tires. The load inflation chart for my 275/70r18s says the tire are rated for a little over 4,000 pounds for the pair at 35psi. I don’t go that low as they feel too mushy under about 55psi. I run 60psi which according to the chart is a little over 6,000 pounds for the pair. That’s more than enough for most of the time when I’m not towing our 5th wheel, big boat, or hauling a pallet of mulch. Then it’s 80psi good for 7,280 pounds. I don’t run 80psi all the time because the tires a way over inflated at that pressure on loaded and the truck rides like a wooden wheeled wagon.

That leaves tire size. As an example, a 275/65r18 is an option on the F250, but not the F350 SRW. It’s only a little smaller than the 275/70r18, but because it has less volume it’s only rated for 6,830 pounds. That’s less than the 7,200 rear axle rating on the F350 SRW.

What those guys said in the click clack link posted earlier about risking a blowout if you run the max psi listed on the sidewall is not true. More pressure equals less flex and less heat in the tire. I don’t remember if it was my parents’ VW or BMW that had a higher recommended pressure for the rear tires if you planned on sustained speeds above 80mph.

Too little pressure for the load is what causes blowouts. The tire flexs like crazy, heats up to the point the layers start to delaminated, then the tire loses its ability to hold are and boom! You’ve got a Ford Exploder with Firestones.

Correct me if im wrong but the door plate is for the OEM tires. Aftermarket tires can change the PSI.

The door plate is for the rated load of the vehicle and the correct/recommended pressure of tires installed on the vehicle.

The pressure is factored on the weight/loading of the vehicle and should be adjusted to a PSI that is correct for the load and driving conditions.

The plate, if followed, will be within safe margin.

As stated, the "chalk" test will give a good indication of best pressure as loaded.

It should not be overthought, unless the tires installed are greatly different than the range of tires the manufacture installs, the plate data should be followed.

Dealers put a wide range of make and model tires on the same vehicle model. So, there typically is no "OEM" tire, as in one type/make/model tire for all specific models.

There are exceptions to certain vehicle models that do have a "specific" tire as part of the package.

(When I bought my 2010 F-150 Lariat, the lot had about 20 trucks I looked at and most had different tires, from sport style, to heavy off-road)

The door sticker is for that size and type of tire. I mention type because a lot of people switch tire type on their SUV, 150/1500 pickups, and Jeeps. They’ll switch from a P-metric to an LT tire. At that point you need to ignore the door sticker and go by the load inflation chart for the tire you installed. A P-metric may call for 35psi while an LT tire of similar size will probably need 50psi for the same load.

quote:

Originally posted by Beancooker:
Chalk test. It’s the best test I have used, for tires on a fast sports car to my offroad Jeep.

Buy sidewalk chalk. Park car with tires at operating temps. Scrub a line of chalk about three inches wide across each each tire. Drive forward slowly, without turning. Pull far enough forward to see the chalk on the tires.

If the tires edges are chalked, pressure is too high. If the center is chalked, pressure is too low.

It takes some time to get the pressures dialed in, but it is a very effective way to make certain you have the largest contact patch if the tread on the pavement. I have done this on every car I have owned for more than 15 years.

This video (Jeep tires are a lot easier to see) demonstrates it very well.


[FLASH_VIDEO]<iframe frameborder="0" height="630" src="https://www.youtube.com/embed/W0qL20nBNRI" width="1120"></iframe>[/FLASH_VIDEO]

Most of the time I agree to use the pressure on the door tag ... on other times depending on the situation I do what Beancooker shared here with the caulk.

quote:

Originally posted by NavyGuy:
I run my Tacoma higher than what's on the door. Door says 35, I run at 38. I've done the chalk test and with my load, 38 gives the cleanest line side to side. Plus a bit higher should help a tinny bit with MPG.

Similar I go up 1 PSI at all 4 corners in my truck. DD car I stick to the plate listed PSI. Performance car I’ll run a few PSI lower than the plate and my bikes I definitely do not run suggested PSI at all.

It’s a variable thing but you daily driver type vehicle, just stick to the plate if you haven’t altered size or width of the tires, and check PSI at least once a month. Once every 2 weeks when temp is fluctuating. And rotate them hos on the reg.

Go by the plate on the door. I usually add another 2 psi to whatever the plate says just because I like a slightly firmer ride etc.

As I understand it the ‘correct’ answer is to go by the door jam, with OEM tires, or rated the same replacements.

That said, I feel there’s room to improvise if desired. When I drive a 2500 truck, I was usually a fair bit below 80 psi driving around empty, most of the time.

Yes, the door jam factors in ride comfort, component stress, handling & other issues. I had a Tacoma years back, the truck would almost want to hop off the road with high psi & bumps.

It’s close to an oil discussion, multiple ways to go without causing problems.