Tire Pressure On Larger Tires?

[Godfadr]

I threw on some 285/75/R18's on the Gladiator. The Cold PSI of those tires is 80psi!

I was running the old ones around 36psi. Any feedback on what to run these new ones at?

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[Mr._Bill]

I threw on some 285/75/R18's on the Gladiator. The Cold PSI of those tires is 80psi!

I was running the old ones around 36psi. Any feedback on what to run these new ones at?

I would start with the Max PSI listing on the side of the tire, and go down from there. They will probably ride a little better around 65psi.

I have not looked at the Max PSI listing on my stock tires. They came from the dealer at 36psi cold, which is the factory recommended pressure for the stock tires.

 

[Oscar Indy]

Jesus NO don't put them at 80psi.

Start at the door pressure and do a chalk test till you have an even contact.

A load range E tire can carry 3200lbs at 80psi.
Considering a JT is roughly 5050 lbs you only need 1/3rd of the load capacity of each tire..... Which puts your minimum psi at about 24 PSI

 

[Renegade]

Jesus NO don't put them at 80psi.

Start at the door pressure and do a chalk test till you have an even contact.

A load range E tire can carry 3200lbs at 80psi.
Considering a JT is roughly 5050 lbs you only need 1/3rd of the load capacity of each tire..... Which puts your minimum psi at about 24 PSI

This is mostly correct. 80 psi is absolutely crazy for a Jeep. I don’t know that a direct proportional reduction in psi vs. max load is best, but it’s more correct than 80 psi. I would suggest that somewhere around 30 psi might offer a good compromise of tire wear, handling, and fuel economy.

 

[Oscar Indy]

This is mostly correct. 80 psi is absolutely crazy for a Jeep. I don’t know that a direct proportional reduction in psi vs. max load is best, but it’s more correct than 80 psi. I would suggest that somewhere around 30 psi might offer a good compromise of tire wear, handling, and fuel economy.

That's minimum psi not optimal. optimal will be higher but the 24ish will keep the side wall stiff enough to support the vehicle at park. You have to take into account cornering shifts vehicle weight onto the outside tires making their share of the weight temporarily higher. Same with up and down. Assume a 20% load increase during manuvers and you are right near that 30 psi mark.

So Google chaulk test and start at 35 is my suggestion.

 

[JP1]

I threw on some 285/75/R18's on the Gladiator. The Cold PSI of those tires is 80psi!

I was running the old ones around 36psi. Any feedback on what to run these new ones at?

That is NOT the running PSI, that's the MAX PSI.
START at 35 and go down a pound at a time.
Run a chalk test.
DO NOT UNDER ANY CIRCUMSTANCES listen to this bolchit:

I would start with the Max PSI listing on the side of the tire, and go down from there. They will probably ride a little better around 65psi.

WHAT THE HELL IS WRONG WITH YOU???
THAT is just about THE DUMBEST SHIT I'VE EVER HEARD.
DO NOT GIVE ADVICE UNTIL YOU LEARN TO PROCESS OXYGEN IN YOUR BRAIN!
chit...

 

[Mr._Bill]

That is NOT the running PSI, that's the MAX PSI.
START at 35 and go down a pound at a time.
Run a chalk test.
DO NOT UNDER ANY CIRCUMSTANCES listen to this bolchit:

WHAT THE HELL IS WRONG WITH YOU???
THAT is just about THE DUMBEST SHIT I'VE EVER HEARD.
DO NOT GIVE ADVICE UNTIL YOU LEARN TO PROCESS OXYGEN IN YOUR BRAIN!
chit...

Relax. It's only going to affect the ride and fuel economy, not blow the truck up.

He's not running stock tires, and didn't say what he put on it. 65psi will ride better than the 80psi he reported. The MAX PSI is a starting point to go DOWN from, if you don't know what else to do. If the OP knew what to do, he wouldn't be posting here. I never said my suggestion was best, just that it's an option.

By the way, You should learn more about your target, before you start throwing insults. People pay up to $150/hr for my advice, and have been doing so for a very long time.

 

[Renegade]

Relax. It's only going to affect the ride and fuel economy, not blow the truck up.

He's not running stock tires, and didn't say what he put on it. 65psi will ride better than the 80psi he reported. The MAX PSI is a starting point to go DOWN from, if you don't know what else to do. If the OP knew what to do, he wouldn't be posting here. I never said my suggestion was best, just that it's an option.

By the way, You should learn more about your target, before you start throwing insults. People pay up to $150/hr for my advice, and have been doing so for a very long time.

Hmm...what do you do for a living? (You aren’t doing to charge me for answering this question, right?) (Crap! That’s a second question...) Nevermind!

 

[bgenlvtex]

Hahahahaha, holy moley internet tire questions are always a shit show, everybody who ever owned one is an expert.

Please, let me help, I will not provide my career resume nor my compensation, you figure it out if you want.

OP, here is some basic knowledge:
Load capacity is a function of the volume of air, and the pressure of that air.

The tire is a pressure vessel designed to contain the required air volume and pressure to support the load.

As the volumetric capacity of the vessel(tire) increases, the pressure required to support the same load decreases.

In any pneumatic assembly the maximum air pressure is dictated by the maximum pressure rating of the weakest component, in this case the wheel, which is not rated for 80psi (probably 60psi).Never exceed the maximum pressure rating of the lowest rated component

The inflation pressure found embossed on the sidewall is a maximum inflation pressure COLD.

The only time the pressure listed on the sidewall of a tire is the recommended inflation pressure, is when maximum capacity is desired or required.

Now on to OP's original question.

You have reduced section width and increased over all diameter, neither one significantly. My recommendation is use the vehicle manufacturers inflation recommendation as a beginning point and increase/decrease incrementally +/- 2psi at a time until best wear and drive-ability are achieved. Ideally you want the entirety of the tread face in contact with the ground surface, and you want that at the highest pressure you can get it (within a specified range) for reduced rolling resistance and the lowest pressure (again within a specified range) for traction and ride comfort. I'm going to guess that you will end up at 38-44psi.

The risk with using tires rated for higher inflation pressures at relatively low pressures are as follows. The higher inflation pressures require higher tensile ratings for the cord material used in the construction of the tire, with that higher tensile rating typically comes lower flexibility. This reduced flexibility sends stress into other components of the construction that are not necessarily designed to absorb them, generates heat which is the enemy in this case, can result in irregular tread wear, failure at the turn up, belt edge separation, and a host of less common failures.

Don't read that last paragraph as fear mongering, it's there for knowledge and awareness.

Don't mistake "airing down" for low speed off road operation as an argument for low inflation pressures at highway speeds/operation, that argument is not valid.

 

[Mr._Bill]

Hmm...what do you do for a living? (You aren’t doing to charge me for answering this question, right?) (Crap! That’s a second question...) Nevermind!

I participate here for free. I bought a Gladiator in July, and it's the nicest truck I've ever owned. Plus, it's a Jeep.

I started driving in the mid 70's, but I'll be the first to admit I don't know everything. It's not that difficult to tell someone they may not have a good idea, and to not spew insults while doing it.

 

[Renegade]

I participate here for free. I bought a Gladiator in July, and it's the nicest truck I've ever owned. Plus, it's a Jeep.

I started driving in the mid 70's, but I'll be the first to admit I don't know everything. It's not that difficult to tell someone they may not have a good idea, and to not spew insults while doing it.

Sorry I I came across as an ass. I was just trying to make light of it. I like to think of Jeep forums as an encyclopedia of Jeep knowledge (I sure use them as one for my own needs). This is why I try to provide constructive information. Sometimes something gets said which is off base, and I think it’s important to correct bad info quickly so others don’t wind up in the wrong place. Enjoy your Jeep.

 

[Godfadr]

Wow...what the hell did I post LOL -

I never had any intention of going with 80psi...but I never had one that high...so wasn't sure where I would end up. I guessed 38 and will be doing the chalk test from this point.

Thanks Everyone...I think

 

[Renegade]

Wow...what the hell did I post LOL -

I never had any intention of going with 80psi...but I never had one that high...so wasn't sure where I would end up. I guessed 38 and will be doing the chalk test from this point.

Thanks Everyone...I think

The chalk test is great for determining a pressure for even tire wear. I just think there is more to consider than just that. Handling, fuel economy, comfort, and tire wear should all be considered.

 

[Mr._Bill]

The chalk test is great for determining a pressure for even tire wear. I just think there is more to consider than just that. Handling, fuel economy, comfort, and tire wear should all be considered.

This is true. With the Nissan Leaf, we run way high on the pressure to get more range out of the battery. Many start just below MAX listed (usually 51psi) and work down to a comfortable range. I run mine at 45psi, which works good for me, compared to the factory recommended 36psi.

 

[Mr._Bill]

Sorry I I came across as an ass. I was just trying to make light of it. I like to think of Jeep forums as an encyclopedia of Jeep knowledge (I sure use them as one for my own needs). This is why I try to provide constructive information. Sometimes something gets said which is off base, and I think it’s important to correct bad info quickly so others don’t wind up in the wrong place. Enjoy your Jeep.

I have no issues with anything you posted. It is important to correct bad information. Some people just have trouble doing it with a polite manner.

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