Question about tire pressure

[MG1912]

My 2007 Ford F350 6.0 supercab long bed SRW has Nitto Terra Grappler G2 A/T LT295/70R18 E 129/126Q tires front and rear. The truck came with 275/70R18 LRE tires, which were replaced by the previous owner. I wrote to Nitto to ask them about recommended tire pressures for my truck camper application (~3,000 on front axle and ~7,000 on the rear axle). I received what seemed to me like a lawyerly response:

"Based on the information provided, the calculated pressure for your Terra Grappler G2 tires is 65 PSI cold pressure on the front tires and 68 PSI cold pressure on the rear tires. At these inflation pressures, your tires are supporting the same amount of weight as your OEM tires did per the vehicle manufacturer's specifications. For any increase in pressure due to towing, we would recommend referring to your vehicle owner's manual for any instructions."

I was surprised because I would have thought they'd recommend closer to 80 PSI for the rear tires. Is their response cautious due to liability concerns? The reference to OEM tires and the vehicle owner's manual makes me suspect this. Or do the recommended pressures sound right?

[billtex]

Done feeding trolls...later.

[billtex]

I will state again, there is no down side to running the rear tires at max psi. Any TC will heavily load your rear axle. The added safety of running at max psi is well worth a “harsh” ride (which is very unlikely with a TC in the bed).
You risk over heating-and tire failure- if you run low psi.

Why would you risk that?

How many of you have had a tire failure while carrying your TC?

It’s not fun.

I can assure you, you will rethink your strategy and take any safety factor you can get after you have a blowout.

Be safe, Bill

[Kayteg1]

You should go to chart with your tire weight rating, not tire size.

[ryoung]

OP, here is a link to the Nitto Terre Grappler G2 tire sizes.

https://tirepressure.com/nitto-terra-grappler-g2-tire-pressure

Open the link and scroll down to your tire size, click on your size and it will show the inflation level for use in either single or dual configuration.

I read from you post that you are approximating the weight of your front and real axle. Don't guess. Get your truck scaled, if you have not weighed it.

ryoung

[Kayteg1]

Than there always is rule of thumb to inflate the tires to the same % of max pressure, what % of max weight rating they actually carry.

[kohldad]

You and several others here have referenced a "tire inflation chart." I cannot find one from Nitto, which is why I wrote to them.

The tire inflation chart I linked will work and will be within a few pounds of the inflation chart Nitto has but may not be willing to release unless you get to the correct techi. You can thank the liability lawsuits for making it hard to find the charts since they just want the average driver to use the numbers in the door jam. Reason any chart will work is that it is physics that determine how much weight a certain size and psi will work. They don't test every psi to get the loading, they use a formula. The only real difference between different manufacturers is the safety factor and minor differences. Look at multiple tire inflation charts that are available and they will all be almost identical for the same size and load range of the tire. I only referenced the Toyo chart because theirs is the easiest to find. Michelin wasn't even willing to give me the charts, but at least I managed to get hold of a tech who was willing to verbally call out the numbers for my particular tire size which exactly matched the numbers on the Toyo chart.

[DieselBurps]

The tire inflation chart should work for the nittos since it goes by the load index. Find your tire size and load index in the chart and go from there.

For reference I run 37x12.5r18 Falken tires on Method wheels rated at 4,500 lbs. the tires are rated for 4000 lbs at 65 psi.

I am 5000 lbs on the front and 6,800 on the rear

[MG1912]

kohldad wrote:
Running at max only provides a harsher ride and premature wearing of the center. Running to low can cause a catastrophic blowout. So if you aren't sure, run at max.

That said, go to any tire inflation chart for your size tire and use the pressure for your loading. Here is the one for Toyo tires but it's the size and load range that count. Inflation Tables

Though I prefer +10 psi to create a slightly harder sidewall which reduces the sway. If I know I'm going to be doing a lot of mountain back roads, I'll run max to minimize the sway.

You and several others here have referenced a "tire inflation chart." I cannot find one from Nitto, which is why I wrote to them.

[MG1912]

specta wrote:
Are those recommended tire pressures with the truck loaded or empty?

Empty I run 45 in the rear and 50 in the front.

Fully loaded 80 in the rear and 70 in the front.

In my question to Nitto, I specified that I would be carrying around 7,000 pounds on the rear axle and 3,000 pounds on the front axle. Their response is in the quote in my OP above: 65 PSI for the front tires, 68 PSI for the rear tires.

[SidecarFlip]

I go by the door sticker, 80 in the back, 60 in the front but my truck is usually loaded with something, be it camper or a fuel tank or the goose neck.

[specta]

Are those recommended tire pressures with the truck loaded or empty?

Empty I run 45 in the rear and 50 in the front.

Fully loaded 80 in the rear and 70 in the front.

[kohldad]

Running at max only provides a harsher ride and premature wearing of the center. Running to low can cause a catastrophic blowout. So if you aren't sure, run at max.

That said, go to any tire inflation chart for your size tire and use the pressure for your loading. Here is the one for Toyo tires but it's the size and load range that count. Inflation Tables

Though I prefer +10 psi to create a slightly harder sidewall which reduces the sway. If I know I'm going to be doing a lot of mountain back roads, I'll run max to minimize the sway.

[Kayteg1]

billtex wrote:
.
There is no down-side to running at the max in the rear..

Yes, there is and I have dental bills to prove it. :B
Each reputable tire manufacturer will have inflation chart showing recommendations for the load.
End of the story.

[billtex]

Grit dog wrote:
Put 80 in the back tires. No question.
68 is probably the min pressure off the chart for exactly 7000lbs.
But once you're loaded up for a year on the road, 7k is probably a bit light.
65 is about max what you'd want in front but not excessive. With those big tires, maybe a bit lower if it feels rough.

This.
There is no down-side to running at the max in the rear.
Front likely sees very little added load with TC-if any-and you could run these lower.
I run rear at 80psi and front at 55 psi.

[twodownzero]

The pressures recommended seem fine. Bigger tires have more air volume with supports more weight with less pressure. Remember, pressure = force / area. That said, I always air my rear tires up all the way when loaded heavy. I have been running lower pressures in the front though as recommended by the manufacturer, and found that the truck rides better and the tires don't get hot. Also, always check your spare when checking your tire pressures.