For towing the Ps seemed just too soft.

 

I was thinking of trying the stock 39 PSI. Do you think that is too low?

 

While I agree with just about everything you said about tire inflation and size, this statement is completely wrong.

The OEM P tires are more than capable of handling the max payload of the truck when inflated at 35 PSI. You will exceed the axle capacity before you exceed the tire capacity.

2200 lbs times 4 tires comes out to 8800 lbs. The truck payload limit is around 6800 lbs.

 

No, because you use GAWR not GVWR.

Using those 2000# rated P tires, we'll take a 8800# GVWR truck. That truck has a front GAWR of 4800# and a rear GAWR of 6084# (yeah I know, they add up to more than 8800 but that's how it works, total on the two combined can't be over that 8800).

A pair of 2200# tires means the tires are only rated for 4400# on the rear axle, well below the axles capacity of 6084#. While 4400# for the front isn't significantly less than the 4800# limit...

 

So here are the real numbers on my 2009 Ram CC 2WD SLT.

From the door

Front GAWR = 3700 lbs
Rear GAWR = 3900 Lbs
Vehicle GVWR = 6800 lbs => this is the number the manufacturer recommends not to exceed.

Stock OEM tires Goodyear SRAs with a load index of 115 @35 PSI are rated at 2679 lbs

2679 x 2 = 5358 lbs, plenty of margin for either front or rear GAWR

edit, although I'm running p tires with a LI of 115, the P275/60-20 SRAs have a load index of 114 (2601 lbs). You can also find the General Grabber HTS tires in the P275/60-20 in a LI of 119 (2998 lbs)

 

Yep, I don't think they can legally sell the truck where the tires don't at least meet the axles limit.

The numbers I gave were simply to show how you come up with the rating. They were from a 2001 Ford F250 gasser which you obviously shouldn't use a P tire on.


For 90% of 1500 buyers passenger car tires are fine and will offer a smoother ride, better fuel economy and cost less. Which is why they use them at the factory . In the OPs case however, he's pulling 8000#. Even though his original P tires could technically handle it, they are not a good choice for his use...

 

he's worried about the feel of the tires so he may be better served with stiffer sidewalls. Since he's running 33" tires on 20 " wheels, E rated tires may be too hard for everyday use. Probably a good compromise would be 33" tires on 17" wheels.

Some of the way the truck feels could be due to the way the weight distribution hitch is set up. Many folks, including some in this forum, under appreciate a properly set up hitch. The first thing they do is put on air bags or timbrens as a solution to their improperly set up hitch.

The OP's truck is probably around 5,600 lbs with approximately 56% of that on the front tires ~ 3100 lbs and the rest (empty) ~ 2500 lbs on the rear axle. He and his family add up a few hundred more Lbs distributed to the front and rear so the front wheels are up to about 3,250 lbs and the back to about 2,650 lbs,

Once he hooks up the trailer (800 lbs TW) plus all of the other stuff (hitch itself is about 100 lbs) he's got about 3,700 lbs on the rear axle.

He should be able to move off 200 to 300 lbs of that off the axle with a properly set up WDH. So, basically with the OEM tires with a LI of 114 (2601 lbs ea), he's got plenty of safety margin. he's got 5,200 lbs tires carrying a load of 3,500 lbs. The load is only 67% of the capacity, not bad in my book.

 

Sorry - I thought it was obvious I was referring to the Rear Axle, which seems to be the one in question by the OP. And 4400# is considerably less than you'd want for towing a trailer. BTW, the factory tires are rated for more than 2200# at 35 PSI, I was just using that as an example, as I'm pretty sure you could find some tires in that size range with those specs.

Interestingly, my son just bought a '13 1500 Ram, and it's door sticker says 35 PSI (for P275/60R20, same as mine), but my '15 1500 says 39 PSI. What's up with that? My guess is, a way to improve MPG rating for CAFE.