Safe tire pressures with upgraded tires

[Kanuck]

I ordered LT tires on my 2021 XLT and it came with General Grabbers (Summer tires). The door sticker states 41 PSI. The TPM's alarm at 30 Psi and I have to bring the pressure up to around 40 PSI to clear the low tire warning. I have Dura Tracs on for the winter and run they around 35 PSI, still alarms at 30 and needs 40 PSI to clear.

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[diambo4life]

I run 38psi in mine. It rides comfortably.

 

[Kensretired]

I ordered LT tires on my 2021 XLT and it came with General Grabbers (Summer tires). The door sticker states 41 PSI. The TPM's alarm at 30 Psi and I have to bring the pressure up to around 40 PSI to clear the low tire warning. I have Dura Tracs on for the winter and run they around 35 PSI, still alarms at 30 and needs 40 PSI to clear.

I wasn't aware of an alarm when pressures fall below a certain number. Is the alarm a sound or a flashing icon in the cluster? Maybe both? Can you calibrate this 30psi to a preferred setting such as 35psi?

 

[diambo4life]

I wasn't aware of an alarm when pressures fall below a certain number. Is the alarm a sound or a flashing icon in the cluster? Maybe both? Can you calibrate this 30psi to a preferred setting such as 35psi?

You sure can....in Forescan.

 

[Kanuck]

I wasn't aware of an alarm when pressures fall below a certain number. Is the alarm a sound or a flashing icon in the cluster? Maybe both? Can you calibrate this 30psi to a preferred setting such as 35psi?

The alarm is a notice on the IPC when you first start the truck and then an icon in the upper left corner. I suspect it can be adjusted with Forscan. But you can always look and see what the pressure is on the center screen.

 

[jadatis]

If you go from OEM P-tires, wich are allowed to carry maxload up to 99mph AT 35 psi, to LT E- load AT 80 psi, you need about 20 psi higher pressure for the same load as the P-tires.
But mostly OEM adviced pressure is 35 psi, because reference-pressure of P tire, and not calculated for the speed and GAWR's.
If it would be calculated, it most likely will get about 26 psi, so then the LT needs about 45 to 50 psi to cover the same GAWR's
But normal driving axle weights are lower, so yustifies a lower pressure.

The conclusion I drew from the Ford-Firestone- affaire, is that the OEM tires where semi offroad tires, with profile blocks that covered part of sidewal, wich gave higher temperatures.

When this " pigheaded Dutch selfdeclared Tirepressure specialist" calculated the needed pressure for the Ford Explorer, rear came yust to 26 psi with european calculation.
The US calculation before 2006 also came to that thanks to the 10% derating for P-tires for SUV.
So a streettire with same specifications would not fail at 26 psi used.
This all assuming max speed 99mph.

I made a spreadsheet to make pressure /loadcapacity lists, if you give specifications of tire
Then it gives 90% of the loadcapacity calculated for the pressure, with a extra tight formula.

Then you " ONLY" have to determine the axleloads acurately, and search them back in my list.
So dont add reserves yourselfes or devide by 2, all done for you.
Succes with that determining the axleloads, the most tricky part in it all.

That 90% used of loadcapacity for 99mph, I determined to give maximum reserve, with still acceptable comfort and gripp.

If you compare same sise of a LT AT 80 psi tire and P-tire AT 35psi, the P- has more lbs/psi then the LT.

So its logical that LT needs higher pressure for the same load.

Why this is? My idea is next.
The LT is a stiffer tire, to hold the higher pressure in.
This makes the overgoing curve from unloaded radius to flat on the ground, larger.
By that lesser surface on the ground at the same deflection.
Assuming the LT has the same deflection as the P-, to give the same heatproduction, the smaller surface needs higher pressure, to carry the same load.
See the picture I made with paint for it years ago

 

[Polo08816]

80 PSI is the maximum tire pressure for the max load for the tire and nothing more. My 2500 truck had 4 tires rated for maximum load capacity at 80 PSI but I ran the front tires at the Chevy recommended pressure of 55 PSI and the rear tires at 80 PSI as the rear tires carried the payloads.

I would never put 80 PSI tires on a 1500 class pickup as they cost more and the extra capacity cannot be used even with the max payload package. The gating factor for the F-150 is the load capacity of the leaf springs and not the tires.

It's true that the extra capacity cannot be used both legally and mechanically because the limitation is the spring rate of the leaf springs.

However, they will improve your towing experience as the vehicle will feel more stable with the stiffer sidewalls. Of course, this will be at the expensive of unloaded ride comfort.

Load Range E tires will likely outlast P metric tires as long as you put enough miles on them per year before tires dry rot.

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