Recommended Tire Pressure

CalTremor2020

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Disclaimer: I am not working as a tire engineer nor is what I am saying to be taken as gospel.

I did some research into the recommended tire pressures for our trucks today and I thought I would share what I learned. Goodyear doesn’t publish (that I was able to find) a guide for load ratings vs tire pressure but I was able to find one on the Toyo website. According to them FMVSS says the tires must be rated to carry 20% more than their half of the axle weight rating. This is for LT tires. If you want to switch to a P metric tire, you are supposed to subtract 10% from its rated load when selecting the size and pressure. To make a really long story short, below are the numbers for my truck.

-Weights in pounds
-Pressure in PSI measured cold
(Edit: “Target” is the pressure at which you mathematically achieve the specified corner load)
  • Front GAWR: 5200
    • Corner: 2600
      • Below: 2515 @ 40
      • Above: 2730 @ 45
      • Target: 42 (41.977)
    • With 20% Safety Factor: 3120
      • Below: 3000 @ 50
      • Above: 3145 @ 55
      • Target: 55 (54.138)
  • Rear GAWR: 6340
    • Corner: 3170
      • Below: 3145 @ 55
      • Above: 3340 @ 60
      • Target: 56 (55.641)
    • With 20% Safety Factor: 3804
      • Below: 3720 @ 70
      • Above: 3905 @ 75
      • Target: 73 (72.270)
I don’t tow often so my plan is to lose the 20% safety factor and run at 45 front and 60 rear. I can increase to 60/80 if I need to tow or haul closer to the rated limit. If you want to run the calculations for yourself or look at different tires the link to the guide is below. Our stock tire size is on page 23.

You can see why Ford chose the inflation pressures that they did. If you go by the FMVSS requirement of +20% and round up to the nearest 10 you get 60psi front and 80psi rear.

 
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PapaRaptor

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Long story short I run 55/60 front rear, rides good 7K miles so far no troubles.

Only bump up when towing really heavy.

But I often wonder about lowering the threshold on forscan and running 45/55
 

RaptorTremor

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I'm running 45 front and rear. My truck doesn't really get put to work anymore so I run the low pressure.
 

Dare

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Long story short I run 55/60 front rear, rides good 7K miles so far no troubles.

Only bump up when towing really heavy.

But I often wonder about lowering the threshold on forscan and running 45/55
I changed my settings to 55f and 55r. It really doesn’t feel much different from my old settings of 55f and 60r.
 
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CalTremor2020

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35" Toyo MT's running 55f 55r
So, according to their chart (I’m assuming 12.5 width) on page 27, your load rating per corner is 3115 lbs. I’m not sure if 250/350/gas/diesel GAWRs are the same but (based on my trucks GAWRs) you wouldn’t quite reach full rear GAWR with your current pressures. You would need 60 for GAWR of 6340 or 80 to get the 20% safety factor from FMVSS. Of course you may be like me and not need it but it’s interesting to know.
 

Big John Son

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So, according to their chart (I’m assuming 12.5 width) on page 27, your load rating per corner is 3115 lbs. I’m not sure if 250/350/gas/diesel GAWRs are the same but (based on my trucks GAWRs) you wouldn’t quite reach full rear GAWR with your current pressures. You would need 60 for GAWR of 6340 or 80 to get the 20% safety factor from FMVSS. Of course you may be like me and not need it but it’s interesting to know.

Yeah, I rarely have much load on the truck. I do tow a pretty heavy boat a few times a year and will inflate when I do. I hauled my 2 waverunners about 70 miles the other day and didn't bother airing up. I hardly knew they were back there. Good info for sure. I knew this, but cool to see it in black and white. Thanks for sharing!
 
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CalTremor2020

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Long story short I run 55/60 front rear, rides good 7K miles so far no troubles.

Only bump up when towing really heavy.

But I often wonder about lowering the threshold on forscan and running 45/55
Based on the numbers, it seems like 45 is reasonable when not towing or hauling heavy. It even meets the front GAWR, assuming you have symmetric loading. I’m planning to try it once I get forscan. I’ll definitely be checking how hot the treads feel after my first highway run though (I like to worry about things). That’s a 78% increase in contact patch area (rear) compared to the design pressure.
 
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