Tire Pressures

[rickrat]

I had a tire shop tell me today that I an running too much tire pressure. I have an 83 F-350 Steel Flatbed (Im guessing 7000 pounds???) I was running 75 psi rear and 70 psi front. (235/85 16)

They said that empty, I should run 55 rear and 60 front. They went on to show me a chart that shows what pressures should be for an empty truck. They also said that unless I am running a really heavy max. load, that those pressures are fine for that as well. They said I should never need more than 60 in the rear as the truck itself would never be loaded enough for that.

Anyone have any real world experience with this?

 

[Agnem]

They are probably correct. Max air presure is for max load. Any tire is going to develop a radius across the tread without a load at full presure, and this will wear your tread unevenly. As for the actual presure you should use, this would be set by your experience, not so much by what somebody tells you. With your tires inflated the way they are now, do a little experiement. Drive slowly through some fine gravel dust or concrete dust that is thinly spread on concrete , and look at what sticks to your tread. If the dust is all the way across, your fine. If not, air down until it is. Of course if you have a heavy mix of loaded or unloaded, you may have to settle for something in between.

 

[69oiler]

Mel is correct. i run mine around 60 psi for even wear. even when i load the truck down 60 psi carries the load.

trailer tires, on the other hand, should be inflated to max pressure at all times.

 

[Andrew M. Frankli]

I had a beautiful set of Cooper tires last only 1 year. The tread blocks started peeling off the carcass. Went back to the tire dealer and they said I had ruined the tires because of over-inflation. I said the tire says 70lbs.(or whatever) on the sidewall, but he showed me the decal inside the door on my 85 F-250 and it showed something like 55 front and 70 rear. I ran 70 all the way around. They would not warantee the tires. It is interesting, though, that the rear would be 70 when 95 per cent of the time (at least with me), there is MORE weight on the front than the rears. Anyway, that's my experience.

Now I obey the door decal on everything I work on and everything I own.

 

[rickrat]

I would be interested in knowing the weight difference between the front and rear? Im assuming it would be like 70/30 because the weight of the engine.

 

[diesel4me2]

i use whatever is molded on the tire. mine are at 90psi. max load is at 110 psi.
i'll never go over that, but at 90 psi i get even wear across the tire.
chris

 

[Compu Doc]

I run mine at 80. It is what is molded on the tire. I have ran them this way since I had the truck and they ran evenly across. Of course my truck weighs 10,000 empty. But I have also ran my cars the same way and never had a problem.

 

[69oiler]

i think a lot of it had to do with the width of the tire in relation to the rim. a 235 tire will stay flatter at higher pressures than a 265 or wider on stock width rims.

i know if i put more than 60 lbs in my 265s they wear down the middle quickly. even at 60 lbs the middle wears faster but i dont like to pancake my tires out more than they are. also higher pressure usually helps fuel milage.

 

[Full Monte]

If you don't believe the charts, you can adjust your tire pressures using one of the two following tests:

a. Mark a chalk line across the tire tread. Run the vehicle down the street a ways. Stop and look at the chalk line. If it's worn off in the middle of the tread and not on the sides, you have an over-inflated tire.

b. Find or make a small water puddle somewhere. Run your tire through the puddle and travel a couple of revolutions. Get out and look at the pattern the water makes on the asphalt. If the pattern is round, you have over inflation on that tire. If it's square, you have proper inflation. I'm not sure what pattern it makes if you are under-inflated, but you should be adjusting the pressure from the higher air pressures to lower, rather than the other way.

Note that each tire carries a different load and ideally would therefore have a different pressure. Most people just run different pressures front and rear.

 

[Agnem]

That's probably easier than my dust test. As for the door sticker, keep in mind that might only be good if your running the stock recommended tire size too.

 

[dakotajeep]

as 69oiler said you will get better mileage out of running ahigher pressure. I usually run mine 5-10 psi below the max (printed on the tire) evenly all the way around. They will probably wear unevenly but with fuel prices as they are I figureI either replace tires or spend more in fuel.....its probably a wash in the end....

thad

 

[Cat_Rebel]

Not sure but I know load range has alot to do with it too. Load Range E is rated for 80lbs on my 235s & 265s. The tire shop I go in to have them rotated & balenced sets them all at 65lbs & they wear evenly. If they are over inflated you'll notice the center wearing down quick. Still get a nice ride with 60-65lbs

 

[diesel4me2]

Not sure but I know load range has alot to do with it too.

yep, mine are load range F. thats why my door sticker dosen't apply.
chris

 

[Cat_Rebel]

yep, mine are load range F. thats why my door sticker dosen't apply.
chris

Load Range F
I thought E was rather tough!

 

[Mr_Roboto]

The door sticker has the pressures for max GVWR. If you run empty all the time then those pressures are too high.

Same thing the pressure on the sidewall is for max load of the tire, if you are under that load then the pressures are too high.