Determining correct tire pressure for larger tires...help...

[0REDSOX7]

Hi all!

I will preface this with "please don't laugh at me, I am trying to learn..."

On Friday, I upgraded the tires on my 2022 JT Overland from the stock 255/70R18 Bridgestone Dueler H/T 685 to 275/65R18 Falken Wildpeak AT/3. I got the SL load category (same as what was on there).

The tricky part is determining what the tire pressure should now be. The sticker on the door of my JT says cold tire pressure should be 38 Front and 38 Rear. I know that will be too high for these new tires. The receipt from Discount Tire says their calculation should now be 36 PSI, which is where they were. This holds true when you use the Discount Tire "Determining Air Pressure - Load Index Table" going from a 113T to a 116T Standard Load tire.

This evening, after sitting in the garage all day...I decided to do the chalk test.

I started at 36 PSI and got all the way down to 30 PSI on the front before I got uniform even wear. In fact, the rear tires could probably go down a few more PSI, but, assuming I ever carry weight in the back, I'd have issues with a lower tire pressure. 36 PSI vs 30 PSI is quite the difference...

So, with that said, what is correct? The chalk test or the PSI based on the load index?? I am not going to lie, 30 PSI in the front looks as if the tire is a bit "low" on air, but, who knows...

Thoughts here?

Thank you.

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[Rusty PW]

You started with high pressure and worked yourself down. Now start with low pressure and work your way up. You will find the sweet spot is a few psi wide.

 

[0REDSOX7]

Thank you for the reply.

So to make sure I understand, you’re saying now I need to repeat the chalk test going up say 1 PSI each time and see what I get that way?

 

[kevman65]

Google "Tire Chalk Test", watch it several times, then go do it.

Temperature, rubber composition, weight, speed all cause tires to act differently. Manufacturers, both vehicle and tire, have liability to worry about. They are going to err on the high side.

 

[0REDSOX7]

Kevman, I watched several, which is where I got the idea to make sure I did it right.

Just seems that if I do a chalk test with only me driving, and get it right, then the minute I add more people or cargo or anything, then I will now technically be under inflated.

 

[kevman65]

Kevman, I watched several, which is where I got the idea to make sure I did it right.

Just seems that if I do a chalk test with only me driving, and get it right, then the minute I add more people or cargo or anything, then I will now technically be under inflated.

And if it's just you and you drive 20 minutes, it's all changed anyway.

I did it on mine with 35's, came up with 34 psi being the sweet spot, I then played with cold psi readings until I hit what gave me the best number to be 34 psi once tires were warm. That was 31 psi. It's all going to change now that temps are in the 80's during the day.

It's just something you can play with all year round, or just get it close and forget about it.

 

[ShadowsPapa]

Kevman, I watched several, which is where I got the idea to make sure I did it right.

Just seems that if I do a chalk test with only me driving, and get it right, then the minute I add more people or cargo or anything, then I will now technically be under inflated.

Set the pressure for the most common scenario and don't sweat having another 200 pounds in the truck. Worry only when you have hundreds more in there or have a trailer on the back.
Your truck may be heavier or lighter than some other Gladiators and I'd bet that every Overland has the same 38 psi pressure on the door jamb sticker, and likely all Rubicons have 36 psi on that sticker. A few pounds difference in truck weight won't matter. Aim for your most likely situation, how you drive most of the time.
It's going to vary with ambient temperature anyway. If you sweated the details, you'd be adjusting pressure every week, or more often.

 

[Rusty PW]

You'll find the sweet spot might be something like 34 to 36 psi. On that sweet spot. You can always inflate to the higher psi to get you some cushion for extra weight. But if you do carry a heavy load. Then you have to inflate more for that load. And remember that front to rear will be different when empty. On my JTRD. I found 37 front and 34 rear empty.

 

[Rusty PW]

Set the pressure for the most common scenario and don't sweat having another 200 pounds in the truck. Worry only when you have hundreds more in there or have a trailer on the back.
Your truck may be heavier or lighter than some other Gladiators and I'd bet that every Overland has the same 38 psi pressure on the door jamb sticker, and likely all Rubicons have 36 psi on that sticker. A few pounds difference in truck weight won't matter. Aim for your most likely situation, how you drive most of the time.
It's going to vary with ambient temperature anyway. If you sweated the details, you'd be adjusting pressure every week, or more often.

My JTRD has 38 psi on the sticker.

 

[kevman65]

When I got my 35's mounted, the tire shop read the max cold psi on the tires and filled it to that.

70 psi Talk about a bouncy ride

 

[NachoRuby]

My JTRD has 38 psi on the sticker.

That's because you have the "D".

 

[Rusty PW]

When I got my 35's mounted, the tire shop read the max cold psi on the tires and filled it to that.

70 psi Talk about a bouncy ride

Drippling down the highway like a basketball.

 

[Rusty PW]

That's next you have the "D".

What's yo' talkin' 'bout Willis?

 

[NachoRuby]

What's yo' talkin' 'bout Willis?

Damn autocorrect

 

[ShadowsPapa]

My JTRD has 38 psi on the sticker.

Fine - diesels don't count LOL

So that extra PSI is reflecting the heavier truck.

I up the pressure on my rear tires when I tow.

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