84 f250 351w 4x4 no door stickers. What should tire pressure be for some 265/75/16 and also for the stock 235/85/16?
Thanks

 

I believe I am right in saying most of these trucks came from the factory with bias ply tires. I don't know when they switched to radials. So the tire pressures on the sticker would not be correct anyway.

Looks like you might have f250 or f350. If you are going to be hauling with it, on the 235's the max pressure on the sidewall is usually 80psi correct? If you will be hauling heavy, I would run at least 70 psi in them. If not I would run at least 50psi in them for good fuel mileage.

For the wider tire, is it still 80 psi max? (I am assuming these are 10 ply tires). If so, you have to be careful with these on a narrow rim, it will want to wear the middle out of the tire. I would start with 50 psi and see how they wear. A wider tire really needs a wider rim to avoid this problem.

 

On an F-250 or F-350 I'd say the sticker is wrong 95% of the time anyway, even if it's a 2015 truck with the OE tires on it. The load on the truck makes a HUGE difference in the tire pressure you should be running and the sticker assumes you're fully loaded. The 80 psi that's on the sidewall of a 235/85-16 or was probably on your door sticker is great when you're loaded to the max, but it'll give you bad traction, bad ride and bad tire life when you're empty.

One rule of thumb is to draw a chalk line across the tread and drive straight for a few tire revs. If the chalk wears off in the center you should let some air out, if it wears off on the edges you should add more air. You're looking for even wear.

Personally I've always thought that gave a little less air pressure than I wanted to run. Maybe best for tire wear, but lower than I wanted for handling and gas mileage. Still it's a good number to have as a reference.

With 235/85-16 on my '85 F-250 RCLB I ran around 50 F / 35 R empty. Now with my heavier '97 F-250 CCSB I run 60 F / 50 R.

With a wider tire Dave's right, on a narrow rim you'll also wear the center of the tire more, so a lower pressure will be needed, especially to optimize tire wear. Also a wider tire has a larger footprint, so a smaller pressure times a larger area give the same load-carrying force, which would also point you to a lower pressure. However a 265/75-16 is 10.4" wide, 31.6" dia, and a 265/85-16 is 9.3" and 31.7". So the difference in size is pretty small, therefore they'll work pretty well on the stock size rim, and you'll end up pretty close to the same ideal pressure.

 

On my 86 and 87 F250s with 235/85/16s I run 60psi front and rear.

 

There is so much variation in tire size, capacity, ply rating, axle weight, etc. it's impossible to say unless someone has the exact same tires and truck loaded in the exact same way as you.
The best way is to do a chalk test. How to Chalk Tires (5 Steps) | eHow
Or, if you know your axle weight, you can call the tire mfg and they'll tell you what the best inflation is for your specific tire based on the axle weight.

 

Thanks 2 all, I'll get some chalk and give it a try. It has been a long way coming but the old truck isn't to bad, a bit ugly but a strong runner.

 

When would I want to do the chalk test, when tires are cold or when they are hot after driving?

 

At operating temp, since that's when the most wear occurs.

 

If you are looking for longevity I'd set the pressure how they recommend. I change my tire pressure with the weight of my load, terrain, and how long I will be on the road.

If I'm going to the scrap yard or junk yard I will lower my tire pressure to 50 PSI. This helps keep from getting a punctured tire.

Off road I will go down to 40 PSI.

Long highway travels usually 70 PSI

Everyday driving to and from work 60 PSI

Hauling anywhere from 60-75 PSI depending on load

Truck weight will change things as well. Mine is 8,000 lbs unloaded (I have winches mounted to it)

I Have just bought new tires for it though so all that is subject to change, as I will have double bead locks on 37" tires, so I will have to play with the pressures to find what works best.

 

Except tire manufacturers don't provide tire pressure data for vehicles. All they provide is the mas psi at max load.
If you call they will give you the pressure based on your axle weight. At least Cooper will.

 

I meant you all lol I would refer back to the method of chalk you guys refereed to.