Tires: E to D load rating, ford f 250, inflation pressure

Question
QUESTION: I own a Ford F-250 Truck and are in need of new tires. I mainly plow in the winter and do some 4X4 in the summer. I have been researching tires and found that in order to get more aggressive tires I would need to drop to a D rating from the original equipment E rating. I rarely have had any load in the truck. I know from reading other posts that it should be replaced with an E, but is there a possibility of replacing it with a D rating?
ANSWER: Matt,

The answer depends on what the original tire size was on the vehicle and what the inflation pressure is supposed to be - and that information can be found on the vehivle placard - which on a Ford truck is located on the drivers doorpost.

So if you will supply that information, I'll give to an answer.

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QUESTION: The current tires are 265/75/R16 and the inflation is 80psi. I hope to move up in size of tire if that makes a difference.
ANSWER: Matt,

Unfortunately, you didn't actually look at the vehicle placard.  I know that because the truck will show different presssure on the front and rear.  (Unless my book is wrong - which it has been known to be.)

So please verify that you looked at the vehicle placard and not the tire.

Thanks

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QUESTION: It is 55 psi front and 70 rear both when cold if I am reading it correctly. If that is correct should my tires by at that psi constantly? I remember checking them when I got the truck and both were 80

Answer
Matt,

It's a good thing I insisted you look at your vehicle placard, because my answer would have changed based on which of the sets of pressures I went by.

Here's the logic:  The pressure for the rear tires is specified at 70 psi.  A Load Range D only goes up to 65 psi, so a Load Range E - which goes up to 80 psi - is required.

However, if 65 psi were to be used, you'd only lose 200# of load carrying capacity.

The only other thing that concerns me is that altering the pressure ratio front to back is the same as altering the springs - and that can cause handling problems.  But since we are only changing it a little, and there is probably plenty of understeer dialed into the truck, it will probably OK

I don't know what the payload capacity is for your truck, but if you promise never to fully load the truck, and make sure the tires are always inflated to 55 front / 65 rear, it will be OK to use a Load Range D.

Now, it is important that you understand that this exception is because the resulting changes are pretty small.  Normally I don't even discuss changing the pressures.  So be cautious when discussing this change with your friends - this isn't always a small change and I would hate to have folks think this doesn't have risks associated with it.

S